A BUCK converter and a ramp generation circuit therein

Abstract

The application discloses a BUCK converter and a slope generation circuit thereof, which comprises a basic slope generation unit, a first current extraction branch, a second current extraction branch, and a second current source. The first current extraction branch is used for extracting the current of the first current source when the system has a large duty cycle. The second current extraction branch comprises a first current comparator, an RC buffer unit, a buffer, and a third switch tube. The first current comparator is used for comparing the current sizes of the first current source and the second current source. The output end of the first current comparator is connected with the input end of the RC buffer unit. The output end of the RC buffer unit is connected with the input end of the buffer. The output end of the buffer is connected with the gate of the third switch tube. The drain of the third switch tube is connected with the basic slope generation unit, and is used for extracting the current of the first current source. The application can avoid the generation of a large ripple of the output signal of the BUCK system, and improves the stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of power control, and particularly relates to a BUCK converter and a ramp generation circuit therein. Background Art

[0002] In a DCDC switching power supply chip, for example, in a BUCK converter adopting COT control mode, the prior art usually introduces RAMP ramp compensation to reduce jitter. As Figure 1 shown, after introducing ramp compensation, the included angle between the feedback signal FB and the signal EAOUT + VRAMP after ramp compensation will increase to . However, in the case of a large duty cycle, as Figure 2 shown, it is FB that touches VREF. After introducing ramp compensation, the included angle between the feedback signal FB and the signal EAOUT + VRAMP after ramp compensation will become smaller instead. As a result, in the case of a large duty cycle, the system will become unstable.

[0003] To solve this problem, the ramp generation circuit of the prior art often adopts the structure as Figure 3 shown. The left part is for ramp generation. The current source I1 charges the capacitor C1. After the voltage is divided by the resistor, the VRAMP signal is generated. To avoid the system stability problem caused by the ramp in the large duty cycle, the part within the solid line box on the right is added. The current of the current source I1 is drawn away by I2, and I2 can be implemented by two buffer circuits (not shown in the figure). The inputs of the two buffer circuits are Vout and Vin respectively, and Vin and Vout are the input voltage and output voltage of the BUCK converter respectively; the two buffer circuits respectively include resistor R10 and resistor R11, R10 < R11, and I2 = Vout / R10 - Vin / R11. In the case of a large duty cycle, Vout is close to Vin, I2 > I1, and I2 draws away all the charging current of the capacitor, making the voltage of VRAMP be 0, thus avoiding the influence of the ramp generation circuit on the system in the large duty cycle.

[0004] However, Figure 3 the prior art as shown brings new problems. When Vin jumps, for example, Vin instantaneously switches from a low voltage to a high voltage, the current of I2 will suddenly drop to 0, the current drawn away by I1 suddenly decreases, and there will be an obvious spike in VRAMP. With the adjustment of the system loop, the ripple of the system output voltage Vout is relatively large. Therefore, it is necessary to solve the problem of large and unstable output voltage ripple caused thereby. Summary of the Invention

[0005] Purpose of the invention: In order to solve the problem that the ramp generation circuit in the prior art generates spikes due to sudden changes in the input signal of the BUCK converter, resulting in large output signal ripple, the present invention provides a BUCK converter and the ramp generation circuit therein.

[0006] Technical solution: A ramp generation circuit in a BUCK converter, comprising:

[0007] The basic ramp generation unit includes a first current source, a capacitor C1, and a voltage divider resistor. The first current source is used to charge the capacitor C1, the capacitor C1 is used to provide voltage to the voltage divider resistor, and the voltage divider resistor outputs a ramp signal.

[0008] The first current extraction branch includes a second current source, which is used to extract current from the first current source when the system has a large duty cycle.

[0009] The second current extraction branch includes a first current comparator, an RC buffer unit, a buffer, and a third switching transistor. The first current comparator is used to compare the current magnitudes of the first current source and the second current source. The output terminal of the first current comparator is connected to the input terminal of the RC buffer unit, the output terminal of the RC buffer unit is connected to the input terminal of the buffer, the output terminal of the buffer is connected to the gate of the third switching transistor, and the drain of the third switching transistor is connected to the basic ramp generation unit for extracting the current from the first current source.

[0010] Furthermore, the RC buffer unit includes a charging switch Mp1, a discharging switch Mn1, a resistor R4, and a capacitor C2. The source of the charging switch Mp1 is connected to the power supply, the source of the discharging switch Mn1 is grounded, the drains of the charging switch Mp1 and the discharging switch Mn1 are connected to one end of the resistor R4, the other end of the resistor R4 is connected to the capacitor C2 and the input terminal of the buffer, and the gate of the discharging switch Mn1 is connected to the output terminal of the first current comparator.

[0011] Furthermore, the gate of the charging switch Mp1 is connected to the output of the first current comparator.

[0012] Furthermore, the second current extraction branch also includes a second current comparator and a logic OR unit. The second current comparator is used to compare the magnitude of the third current on the first current source and the third switch. The output terminal of the second current comparator is connected to the first input terminal of the logic OR unit, the output terminal of the first current comparator is connected to the second input terminal of the logic OR unit, and the output terminal of the logic OR unit is connected to the gate of the charging switch Mp1.

[0013] Furthermore, the first current comparator includes a first switching transistor, a second switching transistor, and a Schmitt trigger. The source of the first switching transistor is connected to a power supply, the source of the second switching transistor is grounded, the drains of the first and second switching transistors are connected to the input of the Schmitt trigger, the output of the Schmitt trigger is connected to the input of an RC buffer unit, the gate of the first switching transistor is connected to a first current source, and the gate of the second switching transistor is connected to a second current source.

[0014] Furthermore, the second current comparator includes a third switch, a fourth switch, and a Schmitt trigger. The source of the third switch is connected to the power supply, the source of the fourth switch is grounded, the drains of the third and fourth switches are connected to the input of the Schmitt trigger, the output of the Schmitt trigger is connected to the first input of the logic OR unit, the gate of the third switch is connected to the first current source, and the gate of the fourth switch is connected to the output of the buffer.

[0015] A BUCK converter includes the ramp generation circuit described above.

[0016] Compared with the prior art, the BUCK converter and its ramp generation circuit provided by the present invention have the following advantages:

[0017] (1) When the input signal of BUCK changes abruptly, the ramp generation circuit will not generate spikes due to the sudden change in the input signal, thereby avoiding large ripples in the output signal and improving the stability of the BUCK system.

[0018] (2) Further increase the capacitor charging control section so that when the third current exceeds the size of the first current source, the capacitor charging switch can be automatically turned off, thereby maintaining the output voltage of the RC buffer unit within a certain range. The third current will not be too high, and the power consumption can be reduced without affecting the output signal ripple of the system. Attached Figure Description

[0019] Figure 1 The waveforms of each signal under non-large duty cycle conditions using existing technology are shown.

[0020] Figure 2 The waveforms of various signals under large duty cycles are shown in the existing technology.

[0021] Figure 3 A schematic diagram of the structure of a slope generation circuit in the prior art;

[0022] Figure 4 This is a schematic diagram of the ramp generation circuit in Example 1;

[0023] Figure 5 This is a schematic diagram of the ramp generation circuit in Example 2. Detailed Implementation

[0024] The present invention will be further explained and illustrated below in conjunction with the accompanying drawings and specific embodiments.

[0025] Embodiment 1:

[0026] A ramp generation circuit in a BUCK converter, as Figure 4 shown, includes:

[0027] A basic ramp generation unit, which includes a first current source, a capacitor C1, and a voltage-dividing resistor. The first current source is used to charge the capacitor C1. The capacitor C1 is used to provide a voltage for the voltage-dividing resistor. The voltage-dividing resistor divides the voltage and outputs a ramp signal.

[0028] A first current extraction branch, which includes a second current source, used to extract the current of the first current source when the system has a large duty cycle. The second current source can be implemented by two buffer circuits. The inputs of the two buffer circuits are Vout and Vin respectively. Vin and Vout are the input voltage and output voltage of the BUCK converter respectively. The two buffer circuits respectively include a resistor R10 and a resistor R11, where R10 < R11. Let the current of the second current source be I2, then I2 = Vout / R10 - Vin / R11.

[0029] A second current extraction branch, such as Figure 4 the part in the right solid line box in, includes a first current comparator, an RC buffer unit, a buffer, and a third switching transistor (such as a MOS transistor). The first current comparator is used to compare the currents of the first current source and the second current source. The output terminal of the first current comparator is connected to the input terminal of the RC buffer unit. The output terminal of the RC buffer unit is connected to the input terminal of the buffer. The output terminal of the buffer is connected to the gate of the third switching transistor. The drain of the third switching transistor is connected to the basic ramp generation unit, used to extract the current of the first current source.

[0030] The first current comparator is as Figure 4 shown in, and includes a first switching transistor M7, a second switching transistor M8, and a Schmitt trigger. The source of the first switching transistor M7 is connected to the power supply. The source of the second switching transistor M8 is grounded. The drains of the first switching transistor M7 and the second switching transistor M8 are connected to the input terminal of the Schmitt trigger. The output terminal of the Schmitt trigger is connected to the input terminal of the RC buffer unit. The gate of the first switching transistor M7 is connected to the first current source. The gate of the second switching transistor M8 is connected to the second current source.

[0031] The RC buffer unit includes a charging switch Mp1, a discharging switch Mn1, a resistor R4, and a capacitor C2. The source of the charging switch Mp1 is connected to the power supply, and the source of the discharging switch Mn1 is grounded. The drains of the charging switch Mp1 and the discharging switch Mn1 are connected to one end of the resistor R4, and the other end of the resistor R4 is connected to the capacitor C2 and the input terminal of the buffer. The gates of the charging switch Mp1 and the discharging switch Mn1 are both directly connected to the output terminal of the first current comparator.

[0032] A BUCK converter comprising the aforementioned ramp generation circuit.

[0033] When Vin is low, I2 > I1, the Schmitt trigger output voltage V_sch = 0, and the V_HOLD voltage slowly rises under the charging effect of capacitor C2. This rise, after passing through the buffer, generates a third current I3 on ​​the third switch. I3 and I2 together draw current from I1. When Vin suddenly rises, I2 instantly decreases to 0. At this point, V_sch rises, but the V_HOLD voltage does not immediately become 0. Instead, it slowly decreases under the control of the RC buffer unit, causing the third current I3 to decrease slowly. The ramp signal voltage VRAMP does not generate a spike, and the ripple fluctuation of the final simulated system output voltage Vout is significantly reduced.

[0034] In this embodiment, the switching transistor can be a MOSFET, or it could be a bipolar transistor or other transistors.

[0035] Example 2:

[0036] The difference between Embodiment 2 and Embodiment 1 is that the second current extraction branch in Embodiment 2 further includes a second current comparator and a logic OR unit, such as... Figure 5 As shown in the solid line box, the second current comparator is used to compare the magnitude of the first current source and the third current on the third switch. The output of the second current comparator is connected to the first input of the logic OR unit, the output of the first current comparator is connected to the second input of the logic OR unit, and the output of the logic OR unit is connected to the gate of the charging switch Mp1.

[0037] The second current comparator includes a third switch, a fourth switch, and a Schmitt trigger. The source of the third switch is connected to the power supply, the source of the fourth switch is grounded, the drains of the third and fourth switches are connected to the input of the Schmitt trigger, the output of the Schmitt trigger is connected to the first input of the logic OR unit, the gate of the third switch is connected to the first current source, and the gate of the fourth switch is connected to the output of the buffer.

[0038] In this embodiment, the gate of the charging switch Mp1 in the RC buffer unit is not directly connected to the output of the first current comparator, but is further controlled through a logic OR unit.

[0039] After V_sch voltage reaches 0, charging switch Mp1 turns on, charging capacitor C2, causing V_HOLD voltage to rise and I3 to rise. When I3 > I1, V_switch voltage is high. Even if V_sch is low, charging switch Mp1 will be turned off under the control of the logic OR unit. At this time, discharging switch Mn1 is also turned off under the action of V_sch, and V_HOLD voltage stabilizes at a certain state. At this time, I3 is approximately equal to I1. Since the function of I3 is to extract I1, considering power consumption, it only needs to be able to extract I1 and does not need to be too large. Therefore, embodiment two can further reduce power consumption while satisfying the requirement of reducing output voltage ripple.

Claims

1. A ramp generation circuit in a BUCK converter, characterized in that, include: The basic ramp generation unit includes a first current source, a capacitor C1, and a voltage divider resistor. The first current source is used to charge the capacitor C1, the capacitor C1 is used to provide voltage to the voltage divider resistor, and the voltage divider resistor outputs a ramp signal. The first current extraction branch includes a second current source, which is used to extract current from the first current source when the system has a large duty cycle. The second current extraction branch includes a first current comparator, an RC buffer unit, a buffer, and a third switching transistor. The first current comparator is used to compare the current magnitudes of the first current source and the second current source. The output terminal of the first current comparator is connected to the input terminal of the RC buffer unit, the output terminal of the RC buffer unit is connected to the input terminal of the buffer, the output terminal of the buffer is connected to the gate of the third switching transistor, and the drain of the third switching transistor is connected to the basic ramp generation unit for extracting the current from the first current source.

2. The ramp generation circuit in the BUCK converter according to claim 1, characterized in that, The RC buffer unit includes a charging switch Mp1, a discharging switch Mn1, a resistor R4, and a capacitor C2. The source of the charging switch Mp1 is connected to the power supply, and the source of the discharging switch Mn1 is grounded. The drains of the charging switch Mp1 and the discharging switch Mn1 are connected to one end of the resistor R4, and the other end of the resistor R4 is connected to the capacitor C2 and the input terminal of the buffer. The gate of the discharging switch Mn1 is connected to the output terminal of the first current comparator.

3. The ramp generation circuit in the BUCK converter according to claim 2, characterized in that, The gate of the charging switch Mp1 is connected to the output of the first current comparator.

4. The ramp generation circuit in the BUCK converter according to claim 2, characterized in that, The second current extraction branch also includes a second current comparator and a logic OR unit. The second current comparator is used to compare the magnitude of the third current on the first current source and the third switch. The output terminal of the second current comparator is connected to the first input terminal of the logic OR unit, the output terminal of the first current comparator is connected to the second input terminal of the logic OR unit, and the output terminal of the logic OR unit is connected to the gate of the charging switch Mp1.

5. The ramp generation circuit in the BUCK converter according to any one of claims 1-4, characterized in that, The first current comparator includes a first switching transistor, a second switching transistor, and a Schmitt trigger. The source of the first switching transistor is connected to a power supply, the source of the second switching transistor is grounded, the drains of the first and second switching transistors are connected to the input of the Schmitt trigger, the output of the Schmitt trigger is connected to the input of an RC buffer unit, the gate of the first switching transistor is connected to a first current source, and the gate of the second switching transistor is connected to a second current source.

6. The ramp generation circuit in the BUCK converter according to claim 4, characterized in that, The second current comparator includes a third switch, a fourth switch, and a Schmitt trigger. The source of the third switch is connected to the power supply, the source of the fourth switch is grounded, the drains of the third and fourth switches are connected to the input of the Schmitt trigger, the output of the Schmitt trigger is connected to the first input of the logic OR unit, the gate of the third switch is connected to the first current source, and the gate of the fourth switch is connected to the output of the buffer.

7. A BUCK converter, characterized in that, Includes the ramp generation circuit in any of the BUCK converters of claims 1-6.

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