Comparator with noise cancellation for switching power converters

Abstract

Comparator circuitry (200) for a power converter is disclosed. In an example, a circuit includes a comparator (204) having a first comparator input, a second comparator input, and a comparator output, the comparator coupled to a power supply terminal (216). The circuit further includes a first transistor (302) coupled between a start-up terminal (120) and the first comparator input and having a control terminal coupled to a switch terminal (104); and a second transistor (304) coupled between the start-up terminal (120) and the second comparator input and having a control terminal coupled to the switch terminal (104). Moreover, a third transistor (316) is coupled between the power supply terminal (216) and the second comparator input, and a voltage reference generator (324) is coupled to the power supply terminal (216) and a control terminal of the third transistor (316).

Description

[0001] This specification relates to power converters and techniques for reducing noise in comparator circuits used in power converters. Background Technology

[0002] Metal-oxide-semiconductor field-effect transistors (MOSFETs) can be used as switches when operating in their transistor / linear region because they exhibit low on-resistance in this operating region. N-channel MOSFETs typically have better mobility than their comparable P-channel counterparts and are therefore a preferred choice for use as switches. Consequently, N-channel MOSFETs are widely used as switches in applications such as DC-DC converters. However, if an N-channel MOSFET is used as a high-side transistor, it may require a voltage greater than the supply voltage (V). DD The gate voltage of the MOSFET is required to fully turn on the device. In some DC-DC converter configurations (e.g., half-bridge configurations), a high input voltage level can disable the direct gate drive circuitry for the high-side N-channel power MOSFET. Therefore, a bootstrap gate driver circuit can be used as follows: When the low-side MOSFET is turned on, the switching terminal is pulled to ground, and the bootstrap capacitor is connected to the high-side N-channel power MOSFET via the bootstrap resistor and bootstrap diode. DD Power supply charging. When the low-side MOSFET is turned off, the energy stored in the bootstrap capacitor becomes a floating bias for the high-side drive circuit to turn on the high-side MOSFET. Significant issues remain regarding the accurate monitoring of the bootstrap voltage in a DC-DC power converter using a bootstrap gate driver. Summary of the Invention

[0003] According to one example, a circuit includes: a comparator having a first comparator input, a second comparator input, and a comparator output, the comparator being coupled to a power supply terminal; a first transistor coupled between a power-on terminal and the first comparator input and having a control terminal coupled to a switch terminal; a second transistor coupled between the power-on terminal and the second comparator input and having a control terminal coupled to the switch terminal; a third transistor coupled between the power supply terminal and the second comparator input; and a voltage reference generator coupled to the power supply terminal and to the control terminal of the third transistor.

[0004] According to another example, a circuit includes: a comparator having a first comparator input, a second comparator input, and a comparator output, the comparator being coupled to a power supply terminal; and a first circuit system coupled to a start-up terminal and a switch terminal, the first circuit system being configured to generate at the first comparator input a first voltage signal proportional to the difference between a start-up voltage at the start-up terminal and a switch voltage at the switch terminal, the first voltage signal containing a first noise component. The circuit further includes: a second circuit system coupled to the power supply terminal and configured to generate a second voltage signal at the second comparator input; and a noise cancellation circuit system coupled to the start-up terminal, the switch terminal, and the second circuit system, the noise cancellation circuit system being configured to introduce a second noise component substantially matching the first noise component into the second voltage signal, wherein the comparator is configured to generate an output signal at the comparator output based on the second voltage signal, the output signal changing from a first value to a second value in response to the first voltage signal exceeding a threshold.

[0005] According to another example, a buck converter includes: a first transistor coupled between an input voltage terminal and a switching terminal; a second transistor coupled between the switching terminal and a ground terminal; a driver coupled to a startup terminal and the switching terminal and having a driver output coupled to a control terminal of the first transistor, the driver being configured to provide a drive signal at the control terminal of the first transistor; and a startup comparator system configured to monitor a startup voltage at the startup terminal. The startup comparator system includes: a comparator having a first comparator input, a second comparator input, and a comparator output, the comparator being coupled to a power supply terminal; a first transistor coupled between the startup terminal and the first comparator input and having a control terminal coupled to the switching terminal; a second transistor coupled between the startup terminal and the second comparator input and having a control terminal coupled to the switching terminal; a third transistor coupled between the power supply terminal and the second comparator input; and a voltage reference generator coupled to the power supply terminal and the control terminal of the third transistor. Attached Figure Description

[0006] Figure 1 It is a diagram of a switching power converter that includes a startup comparator system, based on some examples.

[0007] Figure 2 In the example Figure 1 A block diagram of the startup comparator system.

[0008] Figure 3 In the example Figure 2The circuit diagram of the start comparator system.

[0009] Figure 4 In another example Figure 2 The circuit diagram of the start comparator system.

[0010] Figure 5A It is shown in the example Figure 3 A graph of the switching voltage in circuit 4.

[0011] Figure 5B It is shown in the example Figure 3 A graph showing the measured voltage in circuit 4.

[0012] Figure 5C It is shown in the example Figure 3 A graph of the reference voltage in circuit 4. Detailed Implementation

[0013] Noise cancellation techniques are described in comparator circuit systems for power converter applications. For example, the techniques described herein can be used in various circuits and systems incorporating DC-DC switching power converters (e.g., buck converters). In some examples, the techniques can be applied to a startup comparator system in a buck converter (or other type of DC-DC power converter) to monitor the startup capacitor voltage. As described in more detail below, the startup comparator system may include a comparator that compares the difference between the startup capacitor voltage and the switching terminal voltage with a reference threshold. The startup comparator system may further include a noise cancellation circuit system to prevent or reduce false triggering of the comparator. In one such example system, the circuitry includes a comparator having a first comparator input, a second comparator input, and a comparator output coupled to a power supply terminal. A first transistor is coupled between the startup terminal and the first comparator input and has a control terminal coupled to the switching terminal. Furthermore, a second transistor is coupled between the startup terminal and the second comparator input and has a control terminal coupled to the switching terminal, and a third transistor is coupled between the power supply terminal and the second comparator input. The circuitry may further include a voltage reference generator coupled to the power supply terminal and the control terminal of the third transistor. These and other aspects are described in more detail below.

[0014] Overview

[0015] As mentioned above, some DC-DC converters using one or more N-channel MOSFETs as high-side switching / power transistors may include a bootstrap gate driver to provide a gate voltage greater than the supply voltage to fully turn on the high-side switching transistor. In some applications, an undervoltage lockout (UVLO) circuit can be used to shut down the DC-DC converter when the startup voltage across the bootstrap capacitor is too low, thereby preventing unpredictable and / or potentially destructive operation of the converter. Specifically, if the difference between the startup voltage across the bootstrap capacitor and the voltage at the switching terminals of the DC-DC converter is insufficient for the high-side circuitry to operate normally, the UVLO circuit can prevent the DC-DC converter from operating. Therefore, the UVLO circuit may include or be coupled to a comparator that will select the startup voltage (V... BOOT ) and the voltage at the switch terminals (V SW The two voltages are compared to provide an indication of when the difference between them has exceeded a threshold (V). THRESH The digital output of the converter. However, such a comparison can be challenging. More specifically, in various DC-DC converters, the high-side transistor and the low-side transistor are switched according to a pulse width modulation (PWM) control signal. During PWM switching, the voltage V at the switching terminals... SW It can have extremely high transient response (e.g., A switching noise value, such as approximately 10 V per nanosecond (ns), can inject noise into the comparator input and significantly affect its operation. For example, this switching noise can cause the comparator to misfire, which in turn can cause the UVLO circuitry to improperly shut down the DC-DC converter. Additionally, high frequencies (e.g., approximately several hundred MHz) may exist due to parasitic effects within the circuit system. One possible way to mitigate the switching noise problem is to place the comparator circuitry entirely on the high-side voltage rail (i.e., V0). BOOT and V SW Between ) and then use a level shifter to shift the comparator output signal down to the low voltage supply (V) DD The level shifter is used in the input field for subsequent processing (e.g., via a UVLO circuit system). However, these level shifters must be able to accept relatively high input voltages (e.g., 20 V or 25 V) and also consume power from the startup voltage (V). BOOT The relatively high current required for these comparators is necessary for faster operation. Therefore, they can occupy a considerable die area. Furthermore, each comparator output uses at least one level shifter. Thus, a circuit containing N comparator outputs also contains N level shifters, which can result in a very large die area and high associated costs.

[0016] Therefore, the techniques described herein provide startup comparator systems that are at least partially unaffected by switching noise injected due to PWM switching, and provide robust and accurate operation even in the presence of switching and other noise. As further described below, some examples of startup comparator systems include circuitry that converts high-side voltage signal information into current, thereby allowing operation entirely at low voltage V... DD The comparison is performed within the domain. This method avoids the use of multiple level shifters, resulting in significant savings in die area occupied by the startup comparator system. According to some examples, the startup comparator system may include: a measurement branch that receives a representation of the startup voltage V. BOOT and switching voltage V SW The signal; and the reference branch, which generates a representation of the threshold V. THRESH The reference signal, V BOOT With switching voltage V SW The difference can be compared with the threshold. Due to coupling caused by parasitic capacitance in the circuit system, the aforementioned switching noise may be injected into the measurement branch of the circuit system. Therefore, in some examples, the circuit system is configured to inject substantially the same amount of noise into the reference branch, so that the comparator differentially does not see the noise increment between its two input signals. Thus, erroneous triggering of the comparator due to switching noise can be reduced or eliminated. In some examples, the circuit system can be implemented with relatively low-area components (particularly compared to level shifters used in some other methods) and consumes low quiescent current from the high-side power rail. Additionally, in some examples, because an internal (e.g., on-chip) reference voltage can be used to generate the threshold V... THRESH Therefore, the circuit system can have good accuracy of the comparator threshold. Thus, a start-up comparator system is provided that achieves more accurate and robust operation with a smaller die area.

[0017] Example circuit system

[0018] Figure 1This is a diagram illustrating an example of a switching power converter 100 including a start-up comparator system 200 according to certain aspects. In the example shown, the switching power converter 100 is configured as a DC-DC buck converter and includes a high-side transistor Q1 and a low-side transistor Q2. The high-side transistor Q1 is coupled between an input voltage terminal 102 and a switching terminal 104. The low-side transistor Q2 is coupled between the switching terminal 104 and a ground terminal 106, which is referred to herein as the ground terminal for ease of description. An input capacitor 108 may be coupled between the input voltage terminal 102 and the ground terminal 106. In some examples, an inductor 110 is coupled between the switching terminal 104 and an output terminal 112, to which an external load may be coupled. An output capacitor 114 may be coupled between the output terminal 112 and the ground terminal 106. The power converter 100 may receive an input voltage V at the input voltage terminal 102. IN And a regulated output voltage V is provided at output terminal 112. OUT .

[0019] As described above, in some examples, the high-side transistor Q1 is an N-channel MOSFET. Figure 1 In the example shown, the high-side transistor Q1 is an N-channel three-terminal enhancement-mode MOSFET with a drain terminal coupled to the input voltage terminal 102 and a source terminal coupled to the switching terminal 104. The high-side gate driver 116 is coupled to the gate control terminal of the high-side transistor Q1 and receives the drive supply voltage V. DRV Similarly, in Figure 1 In the example, the low-side transistor Q2 is an N-channel three-terminal enhancement-mode MOSFET with a drain terminal coupled to the switching terminal 104 and a source terminal coupled to the ground terminal 106. The low-side gate driver 118 is coupled to the gate control terminal of the low-side transistor Q1 and receives the drive power signal V. DRV .

[0020] As described above, the high-side gate driver 116 can be implemented as a bootstrap gate driver. Therefore, the switching power converter 100 may include a bootstrap capacitor 130 coupled across the high-side gate driver 116 between the startup terminal 120 and the switching terminal 104, such as... Figure 1 As shown. As used herein, startup terminal 120 refers to the voltage (V) across bootstrap capacitor 130 that can be sensed or measured. BOOT The terminals of the high-side gate driver 116 are shown. In the example illustrated, the start-up terminal 120 and the switch terminal 104 provide power rails for operation of the high-side gate driver 116. In some examples, a drive power signal V is received there. DRV The drive power terminal 122 is coupled to the start-up terminal 120 via diode 124.

[0021] like Figure 1 As shown, the start comparator system 200 can be coupled to the start terminal 120 to detect the start voltage V. BOOT And coupled to switch terminal 104 to detect switch voltage V SW The comparator system 200 includes a reference terminal 126 at which a reference voltage V is generated. REF As further described below. In some examples, reference terminal 126 is internal to the startup comparator system 200; however, in other examples, reference terminal 126 may be coupled to an external voltage source. The startup comparator system 200 further includes an output terminal 128 at which a comparator output signal COMP_OUT can be provided. In some examples, the comparator output signal COMP_OUT is an indication of the startup voltage V. BOOT With switching voltage V SW Has the difference between them exceeded the reference voltage V? REF The threshold V represents THRESH The digital signal. In some cases, when the start-up voltage V... BOOT With switching voltage V SW The difference between them is less than the threshold V THRESH This can indicate the starting voltage V. BOOT The voltage level is lower than that required for normal operation of the high-side circuitry, as described above. Therefore, output terminal 128 can be coupled to the UVLO circuitry, for example, as described above, when the comparator output signal COMP_OUT indicates that the startup voltage VBOOT is too low, the UVLO circuitry can be used to shut off the power supply to the switching power converter 100 (thereby preventing unpredictable and / or potentially destructive operation of the converter).

[0022] The power converter 100 and its startup comparator system 200 can be implemented wholly or partially using integrated circuits (ICs). In one example, high-side transistor Q1 and low-side transistor Q2, high-side gate driver 116 and low-side gate driver 118, and startup comparator system 200 are formed in a single IC (not shown). In various alternative embodiments, one or more components of these circuits may be implemented externally to the IC. Furthermore, for example, one or more system components of inductor 110 may be disposed "off-chip" and coupled to the IC.

[0023] refer to Figure 2The diagram shows a block diagram of a startup comparator system 200 according to some examples. The startup comparator system 200 includes comparator circuitry 202. In some examples, comparator circuitry 202 includes comparator 204 (which may be a hysteresis comparator) that generates a comparator output signal COMP_OUT at output terminal 128 based on the difference between signals at its two input terminals (labeled "+" and "-"). The startup comparator system 200 may include high-voltage circuitry 210 coupled to startup terminal 120 and switching terminal 104 to receive startup voltage V, respectively. BOOT and switching voltage V SW In some examples, the power converter 100 can have a relatively high input voltage V. IN (For example, operating at approximately 20 V (e.g., in the range of approximately 18 V-22 V, or 20 V ± 10%). Therefore, the switching voltage V SW Alternatively, the voltage at ground terminal 106 (e.g., approximately 0 V) ​​can be compared to the input voltage V. IN The relatively high voltage that transitions between these states. For example, the switching voltage V. SW It can be a square wave or pulse signal that transitions between these two levels (e.g., such as...). Figure 5A As shown above, in order to fully turn on the high-side transistor Q1, the startup voltage V... BOOT It may be necessary to exceed the input voltage V IN And therefore in some examples, it can be as high as approximately 25 V. For example, the startup voltage V BOOT It can exceed the input voltage V IN A transistor gate-source voltage (Vgs). Therefore, the high-voltage circuit 210 receives these potential high-voltage input signals (Vgs). SW and V BOOT And at low pressure V DD A differential signal 218 is generated in the domain, as further described below. Therefore, as Figure 2 As shown, comparator 204 can use a low-voltage power supply V. DD Operation, and therefore can be coupled to power supply voltage terminal 216 (to receive power supply voltage V) DD This is between the differential signal 218 and the ground terminal GND. In some examples, the differential signal 218 represents the startup voltage V. BOOT With switching voltage V SW The difference between them. For example, the differential signal 218 can be compared with the start-up voltage V. BOOT With switching voltage V SW The difference between them is proportional.

[0024] As described above, during the switching of high-side transistor Q1 and low-side transistor Q2, switching noise can couple to the switching voltage V. SWAnd coupled to the startup voltage V BOOT In, such as Figure 2 Box 212 in the diagram represents the signal at the first input of comparator 204 (labeled "+"). Therefore, the signal at the first input of comparator 204 can be the superposition of the differential signal 218 and the coupled noise Vnoise1 (represented by summing block 206). According to some examples, the comparator system 200 includes a noise cancellation circuitry 214 that injects the noise signal Vnoise2 into the reference voltage signal V received at reference terminal 126. REF Therefore, the signal (marked as "-") at the second input of comparator 204 is the reference voltage signal V. REF The noise signal Vnoise2 is superimposed on the injected noise signal Vnoise1 (represented by summing block 208). In some examples, the injected noise signal Vnoise2 is substantially the same as the coupled noise signal Vnoise1 (e.g., within a tolerance of 5% or less). Therefore, because the same noise exists at both comparator inputs, comparator 204 does not respond to the noise, but instead responds based on the differential signal 218 and the reference voltage V. REF The difference between the two signals triggers the circuit and generates the output signal COMP_OUT. Therefore, erroneous triggering due to switching noise can be reduced or eliminated. In some examples, at least some components of the noise cancellation circuit system 214 may be part of the high-voltage circuit 210, as further described below.

[0025] refer to Figure 3 The diagram shows a circuit diagram of an example of a startup comparator system 200. In this example, the high-voltage circuit 210 includes a first transistor 302 and a second transistor 304 coupled to a startup terminal 120 and a switching terminal 104, as shown. In some examples, the first transistor 302 and the second transistor 304 are relatively high-voltage (e.g., 30 V) drain-extended P-channel MOSFETs.

[0026] In some examples, the first transistor 302 has a source terminal coupled to the start-up terminal 120 via a first source resistor 306, a drain terminal coupled to the first input of the comparator 204, and a gate control terminal coupled to the switch terminal 104. A first sensing resistor 310 may be coupled between the drain terminal of the first transistor 302 (and the first input of the comparator 204) and the ground terminal. An input capacitor 314 may be coupled between the start-up terminal 120 and the switch terminal 104, as shown. A capacitor 312 may be coupled across the first sensing resistor 310 (in parallel with the first sensing resistor 310) between the drain terminal of the first transistor 302 and the ground terminal. The first transistor 302 and the first source resistor 306 may form part of a measurement branch that starts the comparator system 200. The second transistor 304 may have a source terminal coupled to the start-up terminal 120 via a second source resistor 308 and a gate control terminal coupled to the switch terminal 104. The second transistor 304 and the second source resistor 308 may be part of the noise cancellation circuit system 214, which is further described below.

[0027] During operation, the first transistor 302 will activate the start-up voltage V. BOOT With switching voltage V SW The differential voltage between (including the superimposed coupled noise signal Vnoise1) is converted into a current I. A The current is then converted back into the voltage of the first sensing resistor 310. This voltage V COMP This is the low-voltage signal input to comparator 204, as shown in the figure. Therefore, the high-voltage circuit 210 serves as the start-up voltage V. BOOT and switching voltage V SW The high voltage domain and the low voltage V of comparator 204 DD Inter-domain interface operations. Signal information from the higher-side domain is converted into current I. A The current generates a voltage V containing signal information when it passes through the first sensing resistor 310. COMP This high-voltage to low-voltage conversion can be achieved without using a level shifter, which, as mentioned above, can consume high current and occupy a large size. In contrast, transistors 302 and 304 can occupy a relatively small size and draw a relatively low quiescent current. In some examples, the quiescent current drawn by the start-up comparator system 200 can be controlled by selecting the values ​​of the first source resistor 306 and the second source resistor 308.

[0028] The comparator system 200 may further include features for generating a reference voltage V. REF The reference branch circuit system 328. In some examples, this reference branch circuit system 328 operates entirely at low voltages (e.g., V). DD(Domain operation.) According to some examples, a reference voltage V is generated across the second sensing resistor 320. REF In some examples, the comparator system 200 includes a voltage reference generator 324 coupled to the power supply voltage terminal 216 of comparator 204. The voltage reference generator 324 is configured to generate a threshold voltage V across resistor 326. THRESH Based on the threshold voltage V across the second sensing resistor 320. THRESH To generate the corresponding reference voltage V REF .

[0029] In some examples, as shown, the start comparator system 200 includes a third transistor 316 coupled between a power supply voltage terminal 216 and a ground terminal. The third transistor 316 may be identical to the first transistor 302 (e.g., of the same type, size, and configuration). Therefore, in some examples, the third transistor 316 is a relatively high-voltage (e.g., 30 V) drain-extended PMOS device having a source terminal coupled to the power supply voltage terminal 216 via a third source resistor 318. The third transistor 316 further has a drain terminal coupled to the drain terminal of the second transistor 304 and the drain terminal of the second input of the comparator 204, and a gate control terminal coupled to the voltage reference generator 324. Therefore, a second sensing resistor 320 is coupled between the drain terminal of the third transistor 316 and the ground terminal. A capacitor 322 may be coupled in parallel with the second sensing resistor 320 between the drain terminal of the third transistor 316 and the ground terminal. In some examples, a resistor 326 (across which it generates a threshold voltage V) THRESH It is coupled between the power supply voltage terminal 216 and the gate control terminal of the third transistor 316.

[0030] In operation, the third transistor 316 can be based on the threshold voltage V. THRESH To generate current I B This current I B It is converted into a reference voltage V across the second sensing resistor 320. REFIn some examples, to properly operate the start comparator system 200, the first source resistor 306 is matched with the third source resistor 318, the first sensing resistor 310 is matched with the second sensing resistor 320, and the first transistor 302 and the third transistor 316 are identical, as described above. For example, for matching, the first source resistor 306 and the third source resistor 318 may have substantially the same resistance value (e.g., within a 5% tolerance), and the first sensing resistor and the second sensing resistor may have substantially the same resistance value (e.g., within a 5% tolerance). Similarly, in some examples, the two capacitors 312, 322 have substantially the same capacitance value (e.g., within a 5% or smaller tolerance). Therefore, in operation, comparator 204 receives at its input a measurement signal V representing the differential signal 218. COMP and representing the reference voltage V REF And therefore, it represents the threshold voltage V. THRESH Reference signal V REF_N Therefore, when the difference signal exceeds the threshold V THRESH At this time, the comparator causes the output signal COMP_OUT to change state (e.g., from high to low or from low to high). It should be understood that the reference voltage V used in the comparison... REF Can be compared with threshold V THRESH Slightly different (e.g., at least across the voltage step of the third transistor 316). Therefore, in order for the comparator 204 to be triggered at the correct level, the voltage reference generator 324 can be configured to generate the threshold voltage V. THRESH It takes into account the reference voltage V REF The value of the voltage difference.

[0031] As described above, the measurement signal V COMP This includes coupled noise Vnoise1. Therefore, the noise cancellation circuit system 214 is operable to cancel the noise from the measured signal V. COMP Noise (Vnoise2), which has the same amount of noise as (Vnoise1), is injected into the reference voltage V. REF In the middle. As mentioned above, and as... Figure 5A As shown, during the switching of transistors Q1 and Q2, the switching voltage V SW It can be approximately 0V and V IN Switching between them, or because the ringing may be more than V IN Several volts high, with potentially very high transients (e.g., ~10V / ns). Reference Figure 4 Due to the parasitic capacitance 402 of the first transistor 302, switching noise can be coupled into the voltage across the first sensing resistor 310. Therefore, referring to... Figure 5B The measurement signal V at the input of the first comparator COMPIncludes a differential signal 218 (start-up voltage V) BOOT With switching voltage V SW The component 502 (the difference between) and the first noise component 504 (e.g., Vnoise1).

[0032] Refer again Figure 4 By adding noise cancellation circuitry 214, the same switching noise can be coupled to the reference voltage V generated across the second sensing resistor 320 due to the parasitic capacitance 404 of the second transistor 304. REF As described above, in some examples, the second transistor 304 has a source terminal coupled to the start-up terminal 120 via a second source resistor 308 and a gate control terminal coupled to the switch terminal 104. The drain terminal of the second transistor 304 may be coupled to the drain terminal of the third transistor 316 and to the second sensing resistor 320. Therefore, the second transistor 304 generates a noise cancellation current based on the differential signal 218 (in the same manner as described above with reference to the operation of the first transistor 302) and noise coupled to the signal via parasitic capacitance 404. By scaling the second source resistor 308, this noise cancellation current can be scaled to a portion of the corresponding measurement path current generated by the first transistor 302. For example, the resistance value of the second source resistor 308 may be several times larger than the resistance value of the first source resistor, such that the noise cancellation current is several times smaller than the measurement current generated by the first transistor 302. In one example, the resistance value of the second source resistor is essentially N times the resistance value of the first source resistor 306 (e.g., within a 5% tolerance), where N is a positive value. In some examples, N is an integer value, such as 5, 8, 10, etc. However, in other examples, other scaling factors can be used. As described above, the quiescent current drawn by the start-up comparator system 200 can be controlled by selecting the resistance values ​​of the two source resistors 306, 308.

[0033] According to some examples, the noise cancellation current generated by the second transistor 304 is converted into a voltage across the second sensing resistor 320, and is therefore injected into the reference voltage V. REF Therefore, refer to Figure 5C The reference signal V exists at the second input of comparator 204 REF_N Includes the reference voltage V REF And it represents the threshold V THRESHThe reference voltage component 506 and the second noise component 508 (e.g., Vnoise2). If the first transistor 302 and the second transistor 304 are substantially identical (e.g., same channel type, same size, same configuration, etc.), then the parasitic capacitances 402, 404 can be substantially identical, and therefore the injected noise signal Vnoise2 can be substantially identical to the coupled noise signal Vnoise1. Therefore, the noise becomes the "common mode" of comparator 204, and therefore may not affect the comparison because almost no differential noise is seen at the comparator input. The difference between the two noise signals Vnoise1 and Vnoise2 may be small enough that it is insufficient to change the state of the comparator output signal COMP_OUT. In fact, comparator 204 is based on the measured signal V COMP Component 502 (representing differential signal 218) and reference signal V REF_N The reference voltage component 506 (representing the threshold voltage V) THRESH The comparator 204 is triggered by the difference between the input and output voltages. Therefore, even in the presence of coupling noise 212, the comparator 204 can be triggered based on the startup voltage V. BOOT With switching voltage V SW The difference between them exceeds the threshold V THRESH And operate accurately and robustly (triggered as expected).

[0034] Figure 4 An example of a voltage reference generator 324 is also shown. In this example, the voltage reference generator 324 includes components coupled to the comparator power supply voltage terminal 216 (to receive the power supply voltage V). DD An operational amplifier 406 (serving as an operating power supply) is coupled to a ground terminal. The operational amplifier 406 may have a first input (labeled "+") coupled to a reference power supply terminal 412 via a resistor divider comprising a first resistor 414 and a second resistor 416 coupled in series between the reference power supply terminal 412 and the ground terminal. Therefore, the operational amplifier 406 receives a scaled version of the reference power supply voltage Vrs at the reference power supply terminal 412 at its first input. A voltage reference generator 324 may further include a transistor 408 having a control terminal coupled to the output of the operational amplifier 406, a first terminal (e.g., a drain terminal) coupled to a resistor 326, and a second terminal (e.g., a source terminal) coupled to a ground terminal via another resistor 410. The second input of the operational amplifier 406 may be feedback-arranged to the second terminal of the transistor 408. Therefore, the voltage reference generator 324 generates a threshold voltage V across the resistor 326 based on the reference power supply voltage Vrs received at the reference power supply terminal 412. THRESHAs described above, this arrangement allows the comparator system to have good accuracy in the comparator threshold because the threshold V for comparison can be generated using an internal (e.g., on-chip) reference supply voltage Vrs. THRESH In some examples, the reference supply voltage Vrs is the bandgap voltage or other internally generated voltage.

[0035] Therefore, aspects and embodiments provide a start comparator system 200 that can be activated relative to a switching voltage V. SW Accurately monitor the start-up voltage V BOOT Furthermore, it operates robustly even in the presence of potentially significant and additionally destructive switching noise. Moreover, the example of the start-up comparator system 200 occupies a significantly smaller die area and consumes less quiescent current than circuit systems that use level shifters to switch from the high-side domain to the low-side domain, thus providing a more efficient solution that also delivers good performance.

[0036] Other examples

[0037] Example 1 is a circuit comprising: a comparator having a first comparator input, a second comparator input, and a comparator output, the comparator being coupled to a power supply terminal; a first transistor coupled between a power-on terminal and the first comparator input and having a control terminal coupled to a switch terminal; a second transistor coupled between the power-on terminal and the second comparator input and having a control terminal coupled to the switch terminal; a third transistor coupled between the power supply terminal and the second comparator input; and a voltage reference generator coupled to the power supply terminal and the control terminal of the third transistor.

[0038] Example 2 includes the circuit described in Example 1, wherein the first, second, and third transistors are drain-extended p-channel field-effect transistors.

[0039] Example 3 includes a circuit according to one of Examples 1 or 2, further comprising: a first resistor coupled between the startup terminal and the first transistor, the first resistor having a first resistance value; a second resistor coupled between the startup terminal and the second transistor, wherein the second resistance value of the second resistor is substantially N times the first resistance value, where N is a positive value; and a third resistor coupled between the power supply terminal and the third transistor, the third resistor having substantially the first resistance value.

[0040] Example 4 includes the circuit described in Example 3, further comprising a fourth resistor coupled between the first transistor and a ground terminal, and a fifth resistor coupled between the second comparator input and the ground terminal, the fifth resistor having substantially the same resistance value as the fourth resistor.

[0041] Example 5 includes the circuit described in Example 4, further comprising a first capacitor coupled in parallel with the fourth resistor, and a second capacitor coupled in parallel with the fifth resistor, the second capacitor having substantially the same capacitance value as the first capacitor.

[0042] Example 6 includes the circuit described in Example 3, further comprising a fourth resistor coupled between the power supply terminal and the control terminal of the third transistor.

[0043] Example 7 includes the circuit according to Example 6, wherein the voltage reference generator is configured to generate a threshold voltage across the fourth resistor, and wherein the comparator is configured to provide an output signal at the comparator output, the output signal changing from a first value to a second value in response to the difference between the start-up voltage at the start-up terminal and the switch voltage at the switch terminal exceeding the threshold voltage.

[0044] Example 8 includes a circuit according to any one of Examples 3 to 7, further comprising a capacitor coupled between the start-up terminal and the switch terminal.

[0045] Example 9 is a DC-DC power converter that includes the circuitry according to any one of Examples 1 to 8.

[0046] Example 10 is a circuit comprising: a comparator having a first comparator input, a second comparator input, and a comparator output, the comparator being coupled to a power supply terminal; a first circuit system coupled to a start-up terminal and a switch terminal, the first circuit system being configured to generate at the first comparator input a first voltage signal proportional to the difference between a start-up voltage at the start-up terminal and a switch voltage at the switch terminal, the first voltage signal containing a first noise component; a second circuit system coupled to the power supply terminal and configured to generate a second voltage signal at the second comparator input; and a noise cancellation circuit system coupled to the start-up terminal, the switch terminal, and the second circuit system, the noise cancellation circuit system being configured to introduce a second noise component substantially matching the first noise component into the second voltage signal, wherein the comparator is configured to generate an output signal at the comparator output based on the second voltage signal, the output signal changing from a first value to a second value in response to the first voltage signal exceeding a threshold.

[0047] Example 11 includes a circuit according to Example 10, wherein the first circuit system includes a first resistor coupled between the first comparator input and a ground terminal, and wherein the first circuit system is configured to convert the voltage difference between the start-up voltage and the switching voltage into a current flowing through the first resistor to generate the first voltage signal, and wherein the second circuit system includes a second resistor coupled between the second comparator input and the ground terminal, the second resistor having substantially the same resistance value as the first resistor.

[0048] Example 12 includes the circuit according to Example 11, wherein the second circuit system includes a voltage reference generator coupled to the power supply terminal and configured to generate a threshold voltage having the threshold; and wherein the second voltage signal is based on the threshold voltage.

[0049] Example 13 includes the circuit according to Example 12, wherein the first circuit system further includes: a third resistor having a first resistor terminal and a second resistor terminal, the first resistor terminal being coupled to the start-up terminal; and a first transistor being coupled between the second resistor terminal and the first comparator input and having a control terminal coupled to the switch terminal.

[0050] Example 14 includes the circuit described in Example 13, wherein the second circuit system further includes: a fourth resistor having a third resistor terminal and a fourth resistor terminal, the third resistor terminal being coupled to the power supply terminal, the fourth resistor having a resistance value substantially the same as the third resistor; and a second transistor coupled between the fourth resistor terminal and the second comparator input and having a control terminal coupled to the voltage reference generator.

[0051] Example 15 includes a circuit according to Example 14, wherein the second circuit system includes a fifth resistor coupled between the power supply terminal and the control terminal of the second transistor; wherein the voltage reference generator is configured to generate the threshold voltage across the fifth resistor.

[0052] Example 16 includes the circuit described in Example 14, wherein the noise cancellation circuit system comprises: a fifth resistor having a fifth resistor terminal and a sixth resistor terminal, the fifth resistor terminal being coupled to the start-up terminal, the resistance value of the fifth resistor being substantially N times the resistance value of the third resistor, where N is a positive value; and a third transistor being coupled between the sixth resistor terminal and the second comparator input and having a control terminal coupled to the switch terminal.

[0053] Example 17 includes the circuit described in Example 16, wherein the first, second, and third transistors are drain-extended p-channel field-effect transistors.

[0054] Example 18 includes a circuit according to any one of Examples 11 to 17, wherein the first circuit system includes a first capacitor coupled in parallel with the first resistor, and wherein the second circuit system includes a second capacitor coupled in parallel with the second resistor, the second capacitor having substantially the same capacitance value as the first capacitor.

[0055] Example 19 is a DC-DC converter that includes the circuitry according to any one of Examples 10 to 18.

[0056] Example 20 is a buck converter comprising: a first transistor coupled between an input voltage terminal and a switching terminal; a second transistor coupled between the switching terminal and a ground terminal; a driver coupled to a startup terminal and the switching terminal and having a driver output coupled to a control terminal of the first transistor, the driver being configured to provide a drive signal at the control terminal of the first transistor; and a startup comparator system configured to monitor a startup voltage at the startup terminal. The startup comparator system includes: a comparator having a first comparator input, a second comparator input, and a comparator output, the comparator being coupled to a power supply terminal; a third transistor coupled between the startup terminal and the first comparator input and having a control terminal coupled to the switching terminal; a fourth transistor coupled between the startup terminal and the second comparator input and having a control terminal coupled to the switching terminal; a fifth transistor coupled between the power supply terminal and the second comparator input; and a voltage reference generator coupled to the power supply terminal and the control terminal of the fifth transistor.

[0057] Example 21 includes a buck converter according to Example 20, wherein the third, fourth, and fifth transistors are drain-extended p-channel field-effect transistors; and wherein the first transistor is an n-channel field-effect transistor.

[0058] Example 22 includes a buck converter according to one of Examples 20 or 21, wherein the startup comparator system further includes: a first resistor coupled between the third transistor and a ground terminal; a second resistor coupled between the second comparator input and the ground terminal, the second resistor having substantially the same resistance value as the first resistor; and a third resistor coupled between the power supply terminal and the control terminal of the fifth transistor.

[0059] Example 23 includes a buck converter according to Example 22, wherein the voltage reference generator is configured to generate a threshold voltage across the third resistor, and wherein the comparator is configured to provide an output signal at the comparator output, the output signal changing from a first value to a second value in response to the difference between the startup voltage and the switching voltage at the switching terminal exceeding the threshold voltage.

[0060] Example 24 is a buck converter comprising: a first transistor coupled between an input voltage terminal and a switching terminal; a second transistor coupled between the switching terminal and a ground terminal; a driver coupled to a startup terminal and the switching terminal and having a driver output coupled to a control terminal of the first transistor, the driver being configured to provide a drive signal at the control terminal of the first transistor; and a startup comparator system configured to monitor a startup voltage at the startup terminal. The startup comparator system includes: a comparator coupled to a power supply terminal and having a first comparator input, a second comparator input, and a comparator output; a first circuit system coupled to the startup terminal and the switch terminal, the first circuit system being configured to generate at the first comparator input a first voltage signal proportional to the difference between a startup voltage at the startup terminal and a switch voltage at the switch terminal, the first voltage signal including a first noise component; a second circuit system coupled to the power supply terminal and configured to generate a second voltage signal at the second comparator input; and a noise cancellation circuit system coupled to the startup terminal, the switch terminal, and the second circuit system, the noise cancellation circuit system being configured to introduce a second noise component substantially matching the first noise component into the second voltage signal, wherein the comparator is configured to generate an output signal at the comparator output based on the second voltage signal, the output signal changing from a first value to a second value in response to the first voltage signal exceeding a threshold.

[0061] In this specification, the term "coupled" may encompass a connection, communication, or signal path that achieves a functional relationship consistent with this specification. For example, if device A generates a signal to control device B to perform an action, then: (a) in a first example, device A is coupled to device B via a direct connection; or (b) in a second example, device A is coupled to device B via an intermediate component C, provided that the intermediate component C does not alter the functional relationship between device A and device B, such that device B is controlled by device A via the control signal generated by device A.

[0062] A device “configured to” perform a task or function can be configured by the manufacturer at manufacturing time (e.g., programmed and / or hardwired) to perform the function and / or can be configured (or reconfigured) by the user after manufacturing to perform the function and / or other additional or alternative functions. Such configuration can be achieved through firmware and / or software programming of the device, through the construction and / or layout of hardware components and the interconnection of the device, or a combination thereof.

[0063] As used herein, the terms “terminal,” “node,” “interconnect,” “pin,” and “lead” are used interchangeably. Unless specifically stated otherwise, these terms are generally used to refer to interconnections or ends between device elements, circuit elements, integrated circuits, devices, or other electronic or semiconductor components.

[0064] The circuits or devices described herein as containing certain components may be substantially adapted to be coupled to those components to form the described circuit system or device. For example, a structure described as containing one or more semiconductor elements (e.g., transistors), one or more passive elements (e.g., resistors, capacitors, and / or inductors), and / or one or more sources (e.g., voltage sources and / or current sources) may conversely contain semiconductor elements within only a single physical device (e.g., semiconductor dies and / or integrated circuit (IC) packages) and may be adapted to be coupled to at least some of the passive elements and / or sources to form the described structure, for example, during or after manufacture by an end user and / or a third party.

[0065] While the use of specific transistors is described herein, other transistors (or equivalent devices) may be used alternatively. For example, a p-channel field-effect transistor (PFET) may be used instead of an n-channel field-effect transistor (NFET) with little or no change to the circuitry. Furthermore, other types of transistors (e.g., bipolar junction transistors (BJTs)) may be used. Additionally, the device may be implemented on / above a silicon (Si), silicon carbide (SiC), gallium nitride (GaN), or gallium arsenide (GaAs) substrate. Furthermore, references to transistor features such as gate, source, or drain are not intended to exclude any suitable transistor technology. For example, features such as source, drain, and gate are generally used to refer to FETs, while emitter, collector, and base are generally used to refer to BJTs. These features may be used interchangeably herein. For example, a reference to the gate of a transistor may refer to the gate of an FET or the base of a BJT, and vice versa. In some examples, a control terminal may refer to the gate of an FET or the base of a BJT. Any other suitable transistor technology may be used. Any such transistor can be used as a switch, where the gate or base or other equivalent feature acts as a switch selection input, which can be driven to connect the source and drain (or, depending on the case, the emitter and collector).

[0066] In this article, "FET" being "on" (or "closed") means that a conductive channel exists in the FET and drain current can flow through it. "FET" being "off" (or "open") means that no conductive channel exists and drain current does not flow through the FET. However, an off-state FET can have current flowing through its body diode.

[0067] The circuits described herein can be reconfigured to include additional or different components to provide functionality at least partially similar to that available before the component replacement. Unless otherwise stated, components shown as resistors generally represent one or more elements coupled in series and / or parallel to provide the amount of impedance represented by the resistor shown. For example, a resistor or capacitor shown and described herein as a single component may alternatively be multiple resistors or capacitors coupled in parallel between the same nodes. For example, a resistor or capacitor shown and described herein as a single component may actually be multiple resistors or capacitors coupled in series between the same two nodes as the single resistor or capacitor.

[0068] The use of the phrase "grounding" in the foregoing description includes chassis grounding, ground wire grounding, floating grounding, virtual grounding, digital grounding, general grounding, and / or any other form of grounding connection applicable to or suited to the teachings herein. In this specification, unless otherwise stated, "about," "approximately," or "substantially" preceding a parameter means within a range of the parameter, for example, within + / -10% or + / -5% of the parameter.

[0069] Modifications may be made to the described examples, and other examples may be made within the scope of the claims.

Claims

1. A circuit comprising: a comparator having a first comparator input, a second comparator input, and a comparator output, the comparator coupled to a power supply terminal; a first transistor coupled between a start terminal and the first comparator input and having a control terminal coupled to a switch terminal; a second transistor coupled between the start terminal and the second comparator input and having a control terminal coupled to the switch terminal; a third transistor coupled between the power supply terminal and the second comparator input; and a voltage reference generator coupled to the power supply terminal and a control terminal of the third transistor.

2. The circuit of claim 1, wherein the first, second, and third transistors are drain extended p-channel field effect transistors.

3. The circuit of claim 1, further comprising: a first resistor coupled between the start terminal and the first transistor, the first resistor having a first resistance value; a second resistor coupled between the start terminal and the second transistor, wherein a second resistance value of the second resistor is substantially N times the first resistance value, where N is a positive value; and a third resistor coupled between the power supply terminal and the third transistor, the third resistor having substantially the first resistance value.

4. The circuit of claim 3, further comprising: a fourth resistor coupled between the first transistor and a ground terminal; and a fifth resistor coupled between the second comparator input and the ground terminal, the fifth resistor having substantially the same resistance value as the fourth resistor.

5. The circuit of claim 3, further comprising: a fourth resistor coupled between the power supply terminal and the control terminal of the third transistor.

6. The circuit of claim 5, wherein the voltage reference generator is configured to generate a threshold voltage across the fourth resistor; and wherein the comparator is configured to provide an output signal at the comparator output that transitions from a first value to a second value in response to a difference between a start voltage at the start terminal and a switch voltage at the switch terminal exceeding the threshold voltage.

7. The circuit of claim 3, further comprising: a capacitor coupled between the start terminal and the switch terminal.

8. A circuit comprising: a comparator having a first comparator input, a second comparator input, and a comparator output, the comparator coupled to a power supply terminal; first circuitry coupled to a start terminal and a switch terminal, the first circuitry configured to produce a first voltage signal at the first comparator input proportional to a difference between a start voltage at the start terminal and a switch voltage at the switch terminal, the first voltage signal including a first noise component; second circuitry coupled to the power supply terminal and configured to produce a second voltage signal at the second comparator input; and a third transistor coupled between the power supply terminal and the second comparator input; and a voltage reference generator coupled to the power supply terminal and a control terminal of the third transistor. ​ noise cancellation circuitry coupled to the start terminal, the switch terminal, and the second circuitry, the noise cancellation circuitry configured to introduce a second noise component substantially matching the first noise component into the second voltage signal; wherein the comparator is configured to generate an output signal at the comparator output based on the second voltage signal, the output signal transitioning from a first value to a second value in response to the first voltage signal exceeding a threshold value.

9. The circuit of claim 8, wherein the first circuitry comprises a first resistor coupled between the first comparator input and a ground terminal, and wherein the first circuitry is configured to convert a voltage difference between the start voltage and a switch voltage into a current flowing through the first resistor to generate the first voltage signal; wherein the second circuitry comprises a second resistor coupled between the second comparator input and the ground terminal, the second resistor having substantially the same resistance value as the first resistor.

10. The circuit of claim 9, wherein the second circuitry comprises a voltage reference generator coupled to the power terminal and configured to generate a threshold voltage having the threshold value; and wherein the second voltage signal is based on the threshold voltage.

11. The circuit of claim 10, wherein the first circuitry further comprises: a third resistor having a first resistor terminal and a second resistor terminal, the first resistor terminal coupled to the start terminal; and a first transistor coupled between the second resistor terminal and the first comparator input and having a control terminal coupled to the switch terminal.

12. The circuit of claim 11, wherein the second circuitry further comprises: a fourth resistor having a third resistor terminal and a fourth resistor terminal, the third resistor terminal coupled to the power terminal, the fourth resistor having substantially the same resistance value as the third resistor; and a second transistor coupled between the fourth resistor terminal and the second comparator input and having a control terminal coupled to the voltage reference generator.

13. The circuit of claim 12, wherein the second circuitry comprises a fifth resistor coupled between the power terminal and the control terminal of the second transistor; wherein the voltage reference generator is configured to generate the threshold voltage across the fifth resistor.

14. The circuit of claim 12, wherein the noise cancellation circuitry comprises: a fifth resistor having a fifth resistor terminal and a sixth resistor terminal, the fifth resistor terminal coupled to the start terminal, the fifth resistor having a resistance value substantially N times a resistance value of the third resistor, where N is a positive value; and a third transistor coupled between the sixth resistor terminal and the second comparator input and having a control terminal coupled to the switch terminal.

15. The circuit of claim 14, wherein the first, second, and third transistors are drain-extended p-channel field effect transistors.

16. The circuit of claim 9, wherein the first circuitry comprises a first capacitor coupled in parallel with the first resistor; and wherein the second circuitry comprises a second capacitor coupled in parallel with the second resistor, the second capacitor having substantially the same capacitance value as the first capacitor.

17. A buck converter comprising: a first transistor coupled between an input voltage terminal and a switch terminal; a second transistor coupled between the switch terminal and a ground terminal; a driver coupled to a start terminal and the switch terminal and having a driver output coupled to a control terminal of the first transistor, the driver configured to provide a drive signal at the control terminal of the first transistor; and a start comparator system configured to monitor a start voltage at the start terminal, the start comparator system including a comparator having a first comparator input, a second comparator input, and a comparator output, the comparator coupled to a power supply terminal, a third transistor coupled between the start terminal and the first comparator input and having a control terminal coupled to the switch terminal, a fourth transistor coupled between the start terminal and the second comparator input and having a control terminal coupled to the switch terminal, a fifth transistor coupled between the power supply terminal and the second comparator input, and a voltage reference generator coupled to the power supply terminal and a control terminal of the fifth transistor.

18. The buck converter of claim 17, wherein the third, fourth, and fifth transistors are drain-extended p-channel field effect transistors; and wherein the first transistor is an n-channel field effect transistor.

19. The buck converter of claim 17, wherein the start comparator system further comprises: a first resistor coupled between the third transistor and a ground terminal; a second resistor coupled between the second comparator input and the ground terminal, the second resistor having substantially the same resistance value as the first resistor; and a third resistor coupled between the power supply terminal and the control terminal of the fifth transistor.

20. The buck converter of claim 19, wherein the voltage reference generator is configured to generate a threshold voltage across the third resistor; and wherein the comparator is configured to provide an output signal at the comparator output that transitions from a first value to a second value in response to a difference between the start voltage and a switch voltage at the switch terminal exceeding the threshold voltage.

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