A method and circuit for measuring transconductance parameters of a switching regulator chip

Abstract

The present invention discloses a method for measuring transconductance parameters of a switching regulator chip, comprising the following steps: S1, connecting a transconductance error amplifier between the FB pin and the COMP pin using an error amplifier to form a feedback loop; S2, applying an external excitation ΔI to the feedback loop using an external current source I, and recording two voltage data of the FB pin before and after the external excitation ΔI is applied; S3, calculating the transconductance parameters of the transconductance error amplifier based on the external excitation ΔI and the two voltage data. Also disclosed is a measurement circuit for the transconductance parameters of a switching regulator chip, which uses the above-mentioned measurement method to measure the transconductance parameters. The present invention can effectively measure the transconductance parameters in the compensation stage loop of the switching regulator chip in combination with the changes before and after the input external excitation; and also performs multiple cyclic measurements to obtain an average value to improve the measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of chip testing, and in particular to a method and a circuit for measuring transconductance parameters of a switching regulator chip. Background Art

[0002] Compared with linear regulators, switching regulators have the characteristics of high efficiency and high power. They can have smaller losses while meeting large output currents. This chip has high efficiency and good stability. Therefore, it is widely used in many electronic devices.

[0003] Transconductance, as an important measurement parameter of the switching regulator chip, needs to add a compensation network to the output of the transconductance error amplifier in the current mode control loop to compensate for the zero poles formed by the power stage, so as to obtain a more reasonable bandwidth and phase.

[0004] At the same time, as a part of the loop, the transconductance error amplifier's transconductance value gm directly participates in the loop's transfer function. It and the compensation network connected to the back stage of the transconductance error amplifier jointly affect the loop's bandwidth and phase, and affect the output transient response and loop stability. Measuring the transconductance value gm of the transconductance error amplifier inside the chip at the board level can not only verify the gm value during the design of the switching regulator, but also better modify the compensation network based on the measured transconductance value, which is of great significance to the transient response and loop stability of the switching regulator.

[0005] However, for the transconductance gm of the switching regulator chip, the design value is generally used as the manual parameter, and there is no clear test method for the external test of the transconductance value of the power chip. This is because the switching regulator loop is a whole. At the chip level after packaging, the transconductance error amplifier cannot be tested separately, the output current of the transconductance error amplifier cannot be sampled, and the transconductance value cannot be calculated. Summary of the invention

[0006] In view of the above problems, the purpose of the present invention is to propose a method and circuit for measuring the transconductance parameters of a switching regulator chip. Based on the output current characteristic of the transconductance error amplifier, the transconductance parameters can be effectively measured in the compensation stage loop of the switching regulator chip in combination with the changes before and after the input external excitation; at the same time, multiple cycles of measurement are performed to obtain the average value to further improve the accuracy of the measurement.

[0007] This is achieved through the following technical solutions:

[0008] In a first aspect, a method for measuring transconductance parameters of a switching regulator chip is proposed, comprising the following steps:

[0009] S1. Between the FB pin and the COMP pin of the switching regulator chip, the error amplifier U1 is used to connect the transconductance error amplifier Gm inside the switching regulator chip to form a feedback loop between the FB pin and the COMP pin of the switching regulator chip; wherein the FB pin is connected in parallel to the output terminal VOUT; the negative phase input terminal of the transconductance error amplifier Gm is connected to the FB pin, and the output terminal of the transconductance error amplifier Gm is connected to the negative phase input terminal of the error amplifier U1 through the COMP pin; S2. An external current source I is added, and the external current source I is used to apply an external excitation ΔI to the feedback loop in step S1, and two voltage data of the FB pin before and after the external excitation ΔI is applied are recorded; S3. Based on the external excitation ΔI and the two voltage data in step S2, the transconductance parameters of the transconductance error amplifier Gm are calculated.

[0010] By adding a feedback loop in the compensation stage loop between the FB pin and the COMP pin, the voltage change of the FB pin can be effectively obtained with the help of the change of the external excitation, and then the transconductance parameter can be measured. The measurement process is fast and efficient.

[0011] Preferably, the method further includes step S4: modifying the magnitude of the external excitation ΔI applied by the external current source I, returning to step S2 for a cycle, obtaining multiple transconductance parameters, and performing data processing on the multiple transconductance parameters to obtain the final transconductance parameter. The magnitude of the external excitation ΔI is modified for a cyclic measurement, thereby determining the accuracy of the measurement and reducing the influence of errors.

[0012] Preferably, the data processing method in step S4 is: averaging multiple transconductance parameters and taking the average value as the final transconductance parameter. averaging multiple measurements can effectively improve accuracy.

[0013] Preferably, the voltage at the non-inverting input terminal of the error amplifier U1 is recorded as V1, and V1 is kept the same as the voltage Vcomp of the COMP pin. When an external excitation ΔI is applied in step S2, ΔI> , where R0 is the equivalent output resistance of the transconductance error amplifier Gm. Limiting the value of ΔI can reduce the impact of the measured error on ΔI.

[0014] Preferably, the output terminal VOUT is connected in parallel with resistors R5 and R6 connected in series, and the resistor R6 is grounded; when the feedback loop is formed in step S1, the negative input terminal of the transconductance error amplifier Gm is connected between the resistor R5 and the resistor R6 through the FB pin. The voltage divider network composed of the resistors R5 and R6 can effectively control the output voltage.

[0015] In the second aspect, the present application also proposes a measurement circuit for the transconductance parameters of a switching regulator chip, and the above-mentioned measurement method is used to measure the switching regulator chip. The measurement circuit includes a transconductance error amplifier Gm, an error amplifier U1, a voltage divider circuit connected in parallel to the output terminal VOUT of the switching regulator chip, an external current source I and a matching filter circuit; wherein the voltage divider circuit includes resistors R5 and R6 connected in series, and the resistor R6 is grounded; the matching filter circuit adopts a grounded RC filter circuit, and the RC filter circuit is connected in parallel between the COMP pin and the negative input terminal of the error amplifier U1; the negative input terminal of the transconductance error amplifier Gm is connected between the resistor R5 and the resistor R6 through the FB pin, and is also connected to the output terminal of the amplifier U1, and the output terminal of the transconductance error amplifier Gm is connected to the negative input terminal of the error amplifier U1 through the COMP pin to form a feedback loop; the external current source I is connected in parallel to the negative input terminal of the error amplifier U1, and is used to apply external excitation ΔI to the feedback loop.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The technical solution of the present invention is based on the characteristic of the output current of the transconductance error amplifier. In combination with the changes before and after the input external excitation in the compensation stage loop of the switching regulator chip, the transconductance parameters can be effectively measured without shutting down, disassembling and reorganizing the switching regulator that has been running. It is extremely efficient and convenient. At the same time, multiple cycles of measurement are performed to obtain the average value, which further improves the accuracy of the measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flow chart of a method for measuring transconductance parameters of a switching regulator chip;

[0019] Figure 2 A schematic diagram of an external circuit structure for measuring transconductance parameters of a switching regulator chip;

[0020] Figure 3 The present invention is a structural schematic diagram of a transconductance error amplifier inside a switching regulator chip connected to an external circuit. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0022] like Figure 1 As shown, it is a flow chart of a method for measuring the transconductance parameters of a switching regulator chip. A negative feedback loop is added between the COMP pin and the compensation stage loop of the FB pin of the switching regulator chip, and then combined with external excitation, the transconductance parameters of the transconductance error amplifier Gm inside the chip are measured.

[0023] The measurement method mainly includes the following steps:

[0024] S1. Between the FB pin and the COMP pin of the switching regulator chip, the error amplifier U1 is used to connect the transconductance error amplifier Gm inside the switching regulator chip to form a feedback loop between the FB pin and the COMP pin of the switching regulator chip. The feedback loop is negative feedback; wherein the FB pin is connected in parallel to the output terminal VOUT; the negative phase input terminal of the transconductance error amplifier Gm is connected to the FB pin, and the output terminal of the transconductance error amplifier Gm is connected to the negative phase input terminal of the error amplifier U1 through the COMP pin.

[0025] like Figure 2 As shown in FIG. 1 , it is a schematic diagram of the external circuit structure when a switching regulator chip is used to measure the transconductance parameters; Figure 3 As shown, it is a schematic diagram of the structure of the transconductance error amplifier inside the switching regulator chip connected to the external circuit; combined with Figure 1 and Figure 2 As shown, the output terminal VOUT of the switching regulator chip is connected in series with resistors R5 and R6, and resistor R6 is grounded. Resistors R5 and R6 form a voltage divider circuit for controlling the output size of the output terminal VOUT so that the output voltage VOUT=V FB × , V FB is the voltage of the FB pin. When the feedback loop is formed in step S1, the negative phase input terminal of the transconductance error amplifier Gm is connected between the resistor R5 and the resistor R6 through the FB pin, and is also connected to the output terminal of the error amplifier U1; the positive phase input terminal voltage of the transconductance error amplifier Gm is Vref, and the positive phase input terminal is also called the common-phase input terminal; the output terminal of the transconductance error amplifier Gm is connected to the negative phase input terminal of the error amplifier U1 through the COMP pin.

[0026] S2. Add an external current source I, use the external current source I to apply an external excitation ΔI to the feedback loop in step S1, and record the two voltage data of the FB pin before and after the external excitation ΔI is applied. The core of this method is to make a negative feedback to the output of the transconductance error amplifier Gm, and give an external excitation to the output at the same time, and observe the difference of the input change, so the transconductance of the transconductance error amplifier Gm can be calculated. The output of the transconductance error amplifier Gm is current, so the type of external excitation is a current source.

[0027] In this embodiment, the output end of the transconductance error amplifier Gm is connected to an output resistor R0 and a parasitic capacitor C6. These two do not actually exist, but are equivalent to internal parameters of the transconductance error amplifier Gm, which are convenient for testing and analysis during actual testing. The voltage of the non-inverting input end of the error amplifier U1 is recorded as V1, and V1 is controlled to be the same as the voltage Vcomp of the COMP pin; when applying an external excitation ΔI in step S2, it is necessary to satisfy ΔI> Limiting the value of ΔI can reduce the impact of measurement errors on ΔI.

[0028] S3. Based on the external excitation ΔI in step S2 and the two voltage data, the transconductance parameter of the transconductance error amplifier Gm is calculated.

[0029] When the switching regulator chip is operating normally and stably, the voltage at the COMP pin remains unchanged, that is, the current inside the switching regulator chip remains unchanged. When no external excitation ΔI is applied, the voltage at the inverting input of the error amplifier U1 is equal to the voltage Vcomp of the COMP pin, and the voltage V1 at the non-inverting input is also equal to Vcomp. The voltage at the output of the error amplifier U1 is equal to the voltage V FB1 , which is also equal to the voltage Vref at the non-inverting input of the transconductance error amplifier Gm. The transconductance parameter is represented by gm. At this time, formula (1) is satisfied: (Vref-V FB1 )×gm=I1; I1 is the output current of the error amplifier U1 at this time.

[0030] When external excitation ΔI is applied, since the chip is still stable, the sampling current remains unchanged, and the output voltage of the transconductance error amplifier Gm remains unchanged, the output current of the transconductance error amplifier Gm will decrease, the transconductance value remains unchanged, and the input voltage difference should decrease. The voltage of the FB pin at this time is recorded as V FB2 , at this time, the input and output of the transconductance error amplifier Gm should satisfy formula (2): (Vref-V FB2 )×gm=I1+ΔI.

[0031] Subtracting formula (1) from formula (2) yields formula (3): (V FB1 -V FB2 )×gm=ΔI.

[0032] By transforming formula (3), we can get the result of transconductance parameter, which is formula (4): gm = At the same time, it can be seen from formula (4) that if the selected ΔI is too small, the input voltage difference of the transconductance error amplifier Gm will be too small, which will be easily affected by the measurement error and make the result inaccurate. Therefore, the selected ΔI must comply with ΔI> limitations, thereby ensuring the accuracy of the measurement.

[0033] By adding a feedback loop in the compensation stage loop between the FB pin and the COMP pin, the voltage change of the FB pin can be effectively obtained with the help of the change of the external excitation, and then the transconductance parameter can be measured. The measurement process is fast and efficient, and there is no need to disassemble, plan and reorganize the circuit connected to the original switching regulator chip. The transconductance parameters of the already running and sealed switching regulator chip can be measured efficiently and conveniently.

[0034] This embodiment further includes step S4: modifying the magnitude of the external excitation ΔI applied by the external current source I, returning to step S2 for a loop, obtaining multiple transconductance parameters, and performing data processing on the multiple transconductance parameters to obtain the final transconductance parameter. The magnitude of the external excitation ΔI is modified for a loop measurement, thereby determining the accuracy of the measurement and reducing the influence of errors.

[0035] In this embodiment, the specific method of data processing in step S4 is: averaging multiple transconductance parameters and taking the average value as the final transconductance parameter. Taking the average value by multiple measurements can effectively improve the accuracy, and if there are individual extreme values, the extreme values ​​often mean that there are some operations or errors that cannot be ignored. At this time, the extreme values ​​can be eliminated first, and then the average value can be calculated to avoid the influence of the extreme values.

[0036] In addition, a measurement circuit for the transconductance parameter of a switching regulator chip is proposed. The switching regulator chip is measured using the above measurement method. The measurement circuit includes a transconductance error amplifier Gm, an error amplifier U1, a voltage divider circuit connected in parallel to the output terminal VOUT of the switching regulator chip, an external current source I, and a matching filter circuit; wherein the voltage divider circuit includes resistors R5 and R6 connected in series, and the resistor R6 is grounded; the matching filter circuit uses a grounded RC filter circuit, and the RC filter circuit is connected in parallel between the COMP pin and the negative phase input terminal of the error amplifier U1; the negative phase input terminal of the transconductance error amplifier Gm is connected between the resistor R5 and the resistor R6 through the FB pin, and is also connected to the output terminal of the amplifier U1, and the output terminal of the transconductance error amplifier Gm is connected to the negative phase input terminal of the error amplifier U1 through the COMP pin to form a feedback loop; the external current source I is connected in parallel to the negative phase input terminal of the error amplifier U1, and is used to apply an external excitation ΔI to the feedback loop. The advantages of the measurement circuit can be referred to the description in the above measurement method, and will not be repeated here.

[0037] Specific application examples:

[0038] Combination Figures 1 to 3As shown, the transconductance parameters of a switching regulator chip TPS54360DDA with a design value of transconductance parameter gm of 1000uS are measured. The allowable input voltage is 8.5V-60V. The switching regulator chip contains nine ports 1-9, which are respectively the BOOT pin for providing startup voltage, the VIN pin for receiving input voltage VIN, the EN pin for controlling the chip switch, the RT / LCK pin for locking state, the SW pin for controlling the output switch, the GND pin for grounding, the COMP pin for forming a compensation stage loop, the FB pin for receiving feedback and forming a compensation stage loop, and the PWRPD pin for indicating that the chip is normal.

[0039] In normal operation of the switching regulator, capacitors C1 and C2 are connected in parallel to the line where the VIN pin receives the input voltage VIN. Both capacitors C1 and C2 are grounded to stabilize the input voltage. Two grounded series resistors R1 and R2 are also connected in parallel to the line. The EN pin is connected between resistors R1 and R2, and the RT / LCK pin is connected between resistor R2 and ground through resistor R3 to form a loop for controlling the state and switch of the switching regulator chip. The GND pin is grounded. The BOOT pin is connected to the output terminal VOUT through capacitor C3 and inductor L1 in turn for external output. The SW pin is connected between inductor L1 and capacitor C3 to control the output switch. At the same time, a grounded B560C diode D1 is also provided between capacitor C3 and inductor L1 to provide a current path for inductor L1 to avoid voltage spikes caused by sudden current interruption and damage to the device. Two grounded capacitors C4 and C5 are connected in parallel at the output end VOUT to stabilize the output; grounded voltage divider series resistors R5 and R6 are also connected in parallel, resistor R6 is grounded, and the FB pin is connected between resistors R5 and R6 through the FB node. A compensation loop is between the COMP pin and the FB pin, and an RC filter circuit and a grounded capacitor C8 are connected in parallel in the loop. The RC filter circuit includes a series resistor R4 and a capacitor C5.

[0040] The sizes of capacitors C1 to C5 and C7 to C8 are 2.2uF, 2.2uF, 0.1uF, 47uF, 47uF, 6800pF and 39pF respectively; the resistance values ​​of resistors R1 to R6 are 523k, 84.5k, 163k, 13k, 53.6k and 10.2k respectively, the inductor L1 is 8.2uH, the input voltage VIN is 12V, and the output VOUT is 5V.

[0041] According to the above measurement method, the error amplifier U1 and the external current source I are added to prepare for the measurement of the transconductance parameter gm.

[0042] When the voltage Vcomp of the COMP pin tends to be stable, Vcomp is measured to be 1.2V, that is, the voltage of the non-inverting input terminal of the transconductance error amplifier Gm is also 1.2V, and the internal reference voltage of the switching regulator chip is 0.6V. At this time, the voltage of the FB pin is measured to be 600.6mV. Then the external excitation applied by the external current source I is set to 1uA, and the voltage of the FB pin is measured again to be 599.55mV. According to formula (4), the transconductance parameter gm=998uS can be calculated, which is very close to the design value of 1000uS.

[0043] In summary, based on the characteristic of the output current of the transconductance error amplifier, the present invention can combine the changes before and after the input external excitation in the compensation stage loop of the switching regulator chip that has been running, and then effectively measure the transconductance parameters. There is no need to shut down, disassemble and reorganize the switching regulator that has been running, which is extremely efficient and convenient. At the same time, multiple cycles of measurement are used to obtain the average value, which further improves the accuracy of the measurement and has significant progress.

[0044] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for measuring transconductance parameters of a switching regulator chip, characterized in that: The steps include: S1, between the FB pin and the COMP pin of the switching regulator chip, the error amplifier U1 is used to connect the transconductance error amplifier Gm inside the switching regulator chip to form a feedback loop between the FB pin and the COMP pin of the switching regulator chip; Among them, the FB pin is connected in parallel to the output terminal VOUT; the negative phase input terminal of the transconductance error amplifier Gm is respectively connected to the FB pin and the output terminal of the error amplifier U1, the output terminal of the transconductance error amplifier Gm is connected to the negative phase input terminal of the error amplifier U1 through the COMP pin, the positive phase input terminal of the transconductance error amplifier Gm is connected to the COMP pin, and the non-phase input terminal of the error amplifier U1 is connected to the COMP pin; S2, adding an external current source I, using the external current source I to apply an external excitation ΔI to the feedback loop in step S1, and recording two voltage data of the FB pin before and after the external excitation ΔI is applied; S3. Based on the external excitation ΔI in step S2 and the two voltage data, the transconductance parameter of the transconductance error amplifier Gm is calculated.

2. A method for measuring transconductance parameters of a switching regulator chip according to claim 1, characterized in that: The method further includes step S4: modifying the size of the external excitation ΔI applied by the external current source I, returning to step S2 to loop, obtaining multiple transconductance parameters, performing data processing on the multiple transconductance parameters, and obtaining final transconductance parameters.

3. A method for measuring transconductance parameters of a switching regulator chip according to claim 2, characterized in that: The data processing method in step S4 is: calculating an average value of multiple transconductance parameters and taking the average value as the final transconductance parameter.

4. A method for measuring transconductance parameters of a switching regulator chip according to claim 1, characterized in that: The voltage at the non-inverting input of the error amplifier U1 is recorded as V1, and V1 is kept the same as the voltage Vcomp of the COMP pin. When an external excitation ΔI is applied in step S2, ΔI> , where R0 is the equivalent output resistance of the transconductance error amplifier Gm.

5. The method for measuring transconductance parameters of a switching regulator chip according to claim 1, characterized in that: The output terminal VOUT is connected in parallel with resistors R5 and R6 connected in series, and the resistor R6 is grounded; when the feedback loop is formed in step S1, the negative phase input terminal of the transconductance error amplifier Gm is connected between the resistor R5 and the resistor R6 through the FB pin.

6. A measurement circuit for transconductance parameters of a switching regulator chip, wherein the measurement method according to any one of claims 1 to 5 is used to measure the switching regulator chip, wherein: The measuring circuit includes a transconductance error amplifier Gm, an error amplifier U1, a voltage divider circuit connected in parallel to the output terminal VOUT of the switching regulator chip, an external current source I and a matching filter circuit; Among them, the voltage divider circuit includes resistors R5 and R6 connected in series, and the resistor R6 is grounded; the matched filter circuit adopts a grounded RC filter circuit, and the RC filter circuit is connected in parallel between the COMP pin and the negative phase input terminal of the error amplifier U1, and the non-phase input terminal of the error amplifier U1 is connected to the COMP pin; the negative phase input terminal of the transconductance error amplifier Gm is connected between the resistor R5 and the resistor R6 through the FB pin, and is also connected to the output terminal of the error amplifier U1, the positive phase input terminal of the transconductance error amplifier Gm is connected to the COMP pin, and the output terminal of the transconductance error amplifier Gm is connected to the negative phase input terminal of the error amplifier U1 through the COMP pin, forming a feedback loop; the external current source I is connected in parallel to the negative phase input terminal of the error amplifier U1, and is used to apply external excitation ΔI to the feedback loop.

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