A pre-charge module and LDO split power-on circuit and chip

Abstract

A pre-charging module and an LDO separate power-on circuit and chip, the circuit comprises: a low dropout linear regulator (LDO) for providing power for a DCDC converter; a pre-charging module, a power output end of the pre-charging module is connected to a power input end of the LDO; an isolation control module, the power output end of the pre-charging module is connected to a power output end of the LDO through the isolation control module; the isolation control module is used for making the power output end of the pre-charging module conduct with the power output end of the LDO after the circuit is enabled and the output voltage of the LDO reaches a predetermined value, otherwise making the power output end of the pre-charging module break with the power output end of the LDO. The chip comprises the above-mentioned circuit for starting the DCDC converter. The present application sets the isolation control module, when the output voltage of the LDO does not reach the predetermined value, the power output end of the pre-charging module is not affected by the large capacitor connected to the power output end of the LDO, so that the charging speed becomes faster, so that the LDO can be established faster.

Description

Technical Field

[0001] This invention relates to electronic circuits, and more specifically to a pre-charge module and an LDO separate power-on circuit and chip. Background Technology

[0002] DC / DC converters are typically used in switching power supply chips. They utilize the energy storage characteristics of capacitors and inductors, and through high-frequency switching via controllable switches (such as MOSFETs), they store the input electrical energy in the capacitors (inductors). When the switch is opened, the electrical energy is released to the load, providing power. DC / DC converters usually require a startup circuit to power on during startup.

[0003] Currently, the startup circuit of existing DC-DC converters typically includes: a pre-power-on module (PREVDD), a bias source module (BIAS), and a low-dropout regulator (LDO). The PREVDD module provides pre-charge power to the LDO and the DC-DC converter's bias source module (BIAS). Once the LDO is established (i.e., reaches a predetermined value), the PREVDD module is turned off. The bias source module (BIAS) generates the reference voltage and reference current required by the DC-DC converter. The LDO powers the relevant modules within the DC-DC converter during operation.

[0004] In existing startup circuits, the output terminals of the PREVDD module and the LDO module are typically shorted together and connected to a 4.7uF capacitor. Furthermore, the power transistors in the PREVDD module are significantly smaller than those in the LDO module. This means the charging current of the PREVDD module is much lower than that of the LDO module, resulting in a very slow charging slope for the PREVDD module and a slower build-up speed. Consequently, this leads to a longer build-up time for the LDO module. This is the fundamental reason for the longer time from receiving the enable signal to the first switching action in a DC-DC converter. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a separate power-on circuit and chip for the pre-charge module and LDO, thereby accelerating the charging speed of the pre-charge module, shortening the setup time of the pre-charge module, and thus saving the time from the start of receiving the enable signal to the first switching action of the DC-DC converter.

[0006] The present invention adopts the following technical solution.

[0007] According to a first aspect of the present invention, a separate power-on circuit for a pre-charge module and an LDO is provided. The circuit includes:

[0008] A low-dropout linear regulator, LDO, is used to provide power to the DC-DC converter;

[0009] A pre-charge module, wherein the power output terminal of the pre-charge module is connected to the power input terminal of the LDO;

[0010] An isolation control module is provided, wherein the power output terminal of the pre-charge module is connected to the power output terminal of the LDO via the isolation control module; the isolation control module is used to connect the power output terminal of the pre-charge module to the power output terminal of the LDO after the circuit is enabled and the output voltage of the LDO reaches a predetermined value, otherwise disconnect the power output terminal of the pre-charge module from the power output terminal of the LDO.

[0011] Furthermore, the isolation control module includes:

[0012] The LDO establishment detection unit is used to detect whether the output voltage and enable signal of the LDO have reached the corresponding predetermined values, and outputs an indication signal; the enable signal is connected to the pre-charge module to control the activation and deactivation of the circuit.

[0013] A controlled switch has a controlled terminal, a first connection terminal, and a second connection terminal. The controlled terminal is used to receive and control the connection and disconnection between the first connection terminal and the second connection terminal according to the indication signal. The first connection terminal is connected to the power output terminal of the pre-charge module, and the second connection terminal is connected to the power output terminal of the LDO.

[0014] Furthermore, the LDO establishment detection unit includes:

[0015] The AND gate receives an LDO setup status signal at its first input and an enable judgment signal at its second input; the enable judgment signal is obtained based on a comparison between the enable signal and a corresponding predetermined value.

[0016] An inverter is used, and the output of the AND gate is connected to the output of the indicator signal via the inverter.

[0017] Furthermore, the LDO establishment detection unit also includes:

[0018] A first resistor (R1') is connected at one end to the output terminal of the inverter, and at the other end to the output terminal of the indicator signal.

[0019] A first capacitor (C1') is connected at one end to the output terminal of the indicator signal, and the other end of the first capacitor (C1') is grounded.

[0020] Furthermore, the isolation control module also includes a second resistor (R2'); the two ends of the second resistor (R2') are respectively connected to the second connection terminal of the controlled switch and the power output terminal of the LDO.

[0021] Furthermore, the isolation control module also includes a second capacitor (C2'); the two ends of the second capacitor (C2') are respectively connected to the controlled end and the first connection end of the controlled switch.

[0022] Furthermore, the controlled switch is a MOS transistor; the gate of the MOS transistor is the controlled terminal, and the source and drain of the MOS transistor are the first connection terminal and the second connection terminal, respectively.

[0023] Furthermore, the power output terminal of the LDO is grounded via a third capacitor (C3').

[0024] Furthermore, it also includes a bias module, wherein the power output terminal of the precharge module is connected to the power input terminal of the bias module.

[0025] According to a second aspect of the present invention, a chip is also provided. The chip includes a pre-charge module and a separate power-on circuit for the LDO as described in the first aspect of the present invention.

[0026] The beneficial effect of this invention lies in the fact that, compared with the prior art, an isolation control module is added between the power output terminal of the LDO and the power output terminal of the pre-charge module. This isolation control module can determine whether the LDO's output voltage has reached a predetermined value. If the LDO's output voltage reaches the predetermined value, the power output terminal of the pre-charge module is connected to the LDO's power output terminal; otherwise, the power output terminal of the pre-charge module is disconnected from the LDO's power output terminal. In this way, when the LDO is not fully charged, the isolation control module prevents the power output terminal of the pre-charge module from being affected by the large capacitance at the LDO's output terminal, thus making the charging speed faster and allowing the LDO to be charged more quickly. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the circuit used to start a DC-DC converter in the prior art;

[0028] Figure 2 This is a schematic diagram of the circuit structure of the precharge module used in the circuit for starting a DC-DC converter in the prior art;

[0029] Figure 3 This is a timing diagram of the setup of the precharge module and LDO in the circuit used to start a DC-DC converter in the prior art;

[0030] Figure 4This is a schematic diagram of the separate power-on circuit for the pre-charge module and LDO of the present invention;

[0031] Figure 5 This is a schematic diagram of the isolation control module in the separate power-on circuit of the pre-charge module and LDO of the present invention;

[0032] Figure 6 This is a timing diagram of the establishment of the pre-charge module and LDO in the separate power-on circuit of the pre-charge module and LDO of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0034] Figure 1 This is a schematic diagram of the startup circuit of a DC-DC converter in the prior art. For example... Figure 1 As shown, the startup circuit of a DC-DC converter in the prior art includes: a precharge module PREVDD, a bias module BIAS, and a low dropout linear regulator module LDO.

[0035] The PREVDD precharge module provides power to the LDO module and the BIAS bias module. Once the LDO module is established, the PREVDD module is turned off. The PREVDD module is connected to the chip's power supply voltage VIN and ground voltage VGND, respectively. It receives the enable signal EN, the bandgap reference establishment judgment signal BGOK, the enable judgment signal ENOK, and the LDO establishment status signal LDOOK, and outputs the precharge voltage.

[0036] The BIAS module is used to generate the reference voltage and reference current required by the DC-DC converter. The BIAS module is connected to the pre-charge voltage and ground voltage VGND, respectively, and outputs the bandgap reference voltage VBG and the bandgap reference establishment judgment signal BGOK.

[0037] The LDO is used to power other modules when the DC-DC converter is operating. The LDO is connected to the power supply voltage VIN and the ground voltage VGND, receives the precharge voltage, the bandgap reference voltage VBG, the enable signal ENOK, and the bandgap reference establishment signal BGOK, and generates the supply voltage VDD.

[0038] Furthermore, the enable signal EN controls the enabling of the entire chip. The enable judgment signal ENOK is a bidirectional input / output signal. EN generates the enable judgment signal ENOK through a comparator (for example, when the enable signal EN rises to 1.2V, the enable judgment signal ENOK goes high). ENOK then serves as an input signal to control other modules of the DC-DC converter, such as the precharge module PREVDD. The bandgap reference establishment judgment signal BGOK is a bidirectional input / output signal. When the bandgap reference voltage VBG rises to a set value, BGOK goes high. BGOK then serves as an input signal to control other modules of the DC-DC converter, such as the precharge module PREVDD. The LDO establishment status signal LDOOK is a bidirectional input / output signal. When the LDO output voltage rises to a predetermined value, LDOOK goes high. LDO then serves as an input signal to control other modules of the DC-DC converter, such as the precharge module PREVDD.

[0039] Specifically, this startup circuit employs a method of short-circuiting the output prevdd of the PREVDD module and the output VDD of the LDO module. Specifically, the voltage VDD output from the LDO module is divided into an analog signal and a digital signal, which power the analog and digital circuits respectively. The VDD signal is connected to the analog signal via a first resistor R1, and the VDD signal is connected to the digital signal via a second resistor R2. The analog signal is directly connected to the output voltage prevdd of the PREVDD module, while the digital signal... Figure 1 This is represented as DVDD. Furthermore, the output of the LDO module is grounded via a capacitor.

[0040] Because the output of PREVDD (i.e. Figure 1 The pre-charge module's (PREVDD) and VDD signals are connected via resistor R1 (12Ω). The LDO's output voltage VDD pin has a large 4.7uF capacitor. Since the power transistor size of the pre-charge module (PREVDD) is much smaller than that of the LDO, the charging current of the pre-charge module (PREVDD) is much smaller than that of the LDO. Therefore, the charging slope of the pre-charge module (PREVDD) is very slow, resulting in a slower build-up speed. This is the fundamental reason for the longer time from EN enable to the first switching action in the DC-DC converter.

[0041] The circuit structure diagram of the precharge module PREVDD used in the prior art is as follows. Figure 2As shown. The precharge module PREVDD includes first and second PMOS transistors MP1 and MP2, first to fifth NMOS transistors MN1 to MN5, resistors R1 to R8, and transistor Q1. The sources of MP1 and MP2 are connected to the chip's power supply voltage VIN. The drain of MP1 and the gates of both MP1 and MP2 are connected to the drain of MN4. The drain of MP2 is connected to ground voltage VGND via R2. The gate of MN4 is connected to ground voltage VGND via R7, and the source of MN4 is connected to the drain of MN1. The source of MN1 is connected to ground voltage VGND via R8, and the gate of MN1 is connected to the enable signal EN via R1. The emitter of transistor Q1 is connected to ground voltage VGND, the base is connected to ground voltage VGND via R8, and the collector is connected to the gate of MN1. The gate of MN5 is connected to the bandgap reference establishment judgment signal BGOK, the source is connected to ground voltage VGND, and the drain is connected to the drain of MN1. The gate of MN3 is connected to the precharge indication signal Prevdd_off, the source of MN3 is connected to the ground voltage VGND, and the drain of MN3 is connected to the gate of MN4. The precharge indication signal Prevdd_off is obtained by ANDing the enable signal ENOK and the LDO setup status signal LDOOK. The two ends of R6 are connected to the power supply voltage VIN and the gate of MN4, respectively. The gate of MN2 is connected to the drain of MP2, the drain of MN2 is connected to the power supply voltage VIN via R3, and the source of MN2 is connected to the ground voltage VGND via R4. The output of the precharge module PREVDD is led out from the source of MN2 and is used to output the precharge voltage prevdd.

[0042] When the power supply voltage VIN and the enable signal EN are powered on, causing MN2 to conduct, VIN charges the output of the precharge module PREVDD through MN2, and the precharge module PREVDD gradually builds up. According to the circuit structure, when VIN and EN are low, for example, when VIN is below 4.5V and EN is below 1.2V, the current of MOSFET MN1 is small, resulting in a very small gate-source voltage VGS of MN2, causing the precharge module PREVDD to build up very slowly.

[0043] Timing diagram for the precharge module PREVDD and LDO setup (below) Figure 3As shown. Because the output of the precharge module PREVDD is shorted to the output of the LDO, the power-on timing waveforms of the precharge module PREVDD and the LDO are consistent. After the power supply voltage VIN is applied, the precharge module PREVDD charges at a very slow rate (because the output terminal of the precharge module PREVDD is shorted to the power output terminal of the LDO and connected to a 4.7uF capacitor). Once the LDO starts working (i.e., after the LDO's output voltage reaches the predetermined value), the charging speeds up due to the addition of the LDO, until the output voltage reaches the fixed voltage of 5V.

[0044] Addressing the problem of existing startup circuits used to start DC-DC converters—namely, the short circuit between the precharge module PREVDD and the LDO output causes the PREVDD to be affected by the 4.7uF capacitor, resulting in slow charging—this invention proposes an improved system with separate power-on circuits and chips for the precharge module and LDO. The specific embodiments of this invention will be described in detail below.

[0045] like Figure 4 According to a first aspect of the present invention, a separate power-on circuit for a precharge module and an LDO is provided. The circuit includes: a low-dropout linear regulator (LDO), a precharge module PREVDD, and an isolation control module ISO. Optionally, the circuit further includes a bias module BIAS.

[0046] A low-dropout linear regulator (LDO) provides power to the DC-DC converter. The power output of the precharge module PREVDD is connected to the power input of the LDO. The power output of the precharge module PREVDD is connected to the power output of the LDO via an isolation control module ISO. The isolation control module ISO connects the power output of the precharge module PREVDD to the power output of the LDO after the LDO's output voltage reaches a predetermined value; otherwise, it disconnects the power output of the precharge module PREVDD from the LDO's power output. The power output of the precharge module PREVDD is connected to the power input of the bias module BIAS to precharge the bias module BIAS. Consistent with existing technology, the power output of the LDO is grounded via a 4.7uF capacitor C3'.

[0047] Furthermore, such as Figure 5 The isolation control module ISO includes an LDO establishment detection unit and a controlled switch.

[0048] The LDO establishment detection unit detects whether the output voltage and enable signal EN of the LDO have both reached predetermined values, and outputs a corresponding indication signal VDD_OFF. Specifically, the LDO detection unit includes an AND gate and an inverter D. The first input of the AND gate receives the LDO establishment status indication signal LDOOK, and the second input receives the enable judgment signal ENOK. The output of the AND gate is connected to the output of the indication signal VDD_OFF via the inverter D. In this way, the LDO detection unit can determine the establishment status of the LDO based on the LDO establishment status signal LDOOK and the enable judgment signal ENOK, thereby outputting the indication signal VDD_OFF.

[0049] The controlled switch has a controlled terminal, a first connection terminal, and a second connection terminal. The controlled terminal is used to receive the indication signal VDD_OFF. The first connection terminal is connected to the power output terminal of the precharge module PREVDD, and the second connection terminal is connected to the power output terminal of the LDO. The controlled terminal is used to control the conduction and disconnection between the first connection terminal and the second connection terminal according to the indication signal VDD_OFF. In this embodiment, the controlled switch uses a MOSFET. The gate of the MOSFET is the controlled terminal, and the source and drain of the MOSFET are the first connection terminal and the second connection terminal, respectively. Specifically, in the precharge module PREVDD... Figure 2 In the circuit shown, the controlled switch preferably uses a PMOS transistor. This is because the source voltage of this MOS transistor is relatively high, close to the VDD voltage. If an NMOS transistor were used, its gate voltage would need to be about 700mV higher than its source voltage to conduct. Therefore, a PMOS transistor is preferred.

[0050] Preferably, the LDO detection unit further includes a first resistor R1' and a first capacitor C1'. One end of the first resistor R1' is connected to the output terminal of the inverter, and the other end of the first resistor R1' is connected to the output terminal of the indicator signal. One end of the first capacitor C1' is connected to the output terminal of the indicator signal VDD_OFF, and the other end of the first capacitor C1' is grounded (i.e., connected to ground potential VGND).

[0051] Preferably, the isolation control module ISO further includes a second capacitor C2'. The two ends of the second capacitor C2' are respectively connected to the controlled terminal and the first connection terminal.

[0052] The first resistor R1' and the first capacitor C1' mentioned above can form an RC circuit. The purpose of this RC circuit and the second capacitor C2' is to buffer the critical points when the precharge module PREVDD and LDO are separated or shorted, to prevent the output voltage of the precharge module PREVDD from having excessive undershoot, which could cause the output signal of the PREVDD power supply module, such as BGOK, to erroneously flip.

[0053] Preferably, the isolation control module further includes a second resistor R2'. The two ends of the second resistor R2' are respectively connected to the second connection terminal and the power output terminal of the LDO. The purpose of setting the second resistor R2' is to prevent latch-up events. Specifically, latch-up occurs because parasitic PNP and NPN type BJTs in the chip layout cause a large current to flow from the power supply voltage VIN to the ground voltage VGND, burning out the chip. Adding resistor R2' avoids the generation of parasitic PNP BJTs and reduces the large current flow from the power supply voltage VIN to the ground voltage VGND.

[0054] In the circuit for starting the DC-DC converter of this invention, the timing diagram of the precharge module PREVDD and LDO being powered on separately is as follows: Figure 6 As shown, the power output terminal of the precharge module PREVDD is not directly connected to the 4.7uF capacitor C3', thus the power-up speed is faster, and the precharge module PREVDD rises to about 4.3V and stabilizes. When the enable signal ENOK and the bandgap reference establishment signal BGOK go high, the LDO starts to work and outputs VDD. However, the size of the power transistor in the LDO is much larger than that in the precharge module PREVDD, so the charging slope is much larger than that of the precharge module PREVDD. When the LDO establishment status signal LDOOK indicates that the LDO output voltage has reached the predetermined value, the power output terminals of the precharge module PREVDD and the LDO are directly shorted through a MOS switch, so that the power-up slopes of the precharge module PREVDD and the LDO are the same.

[0055] According to a second aspect of the invention, a chip is provided that includes a precharge module and an LDO separate power-on circuit as described in the first aspect of the invention.

[0056] The beneficial effect of this invention lies in the fact that, compared with the prior art, an isolation control module is added between the power output terminal of the LDO and the power output terminal of the pre-charge module. This isolation control module can determine whether the LDO's output voltage has reached a predetermined value. If the LDO's output voltage reaches the predetermined value, the power output terminal of the pre-charge module is connected to the LDO's power output terminal; otherwise, the power output terminal of the pre-charge module is disconnected from the LDO's power output terminal. In this way, when the LDO's output voltage has not reached the predetermined value, the isolation control module prevents the power output terminal of the pre-charge module from being connected to the LDO's power output terminal. The pre-charge module is not affected by the large capacitance at the LDO's output terminal, thus the charging speed is faster, allowing the LDO to build up more quickly.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A separate power-on circuit for the pre-charge module and the LDO, characterized in that, include: Low dropout linear regulators, LDOs, are used to provide power to DC-DC converters; A pre-charge module, wherein the power output terminal of the pre-charge module is connected to the power input terminal of the LDO; An isolation control module is provided, wherein the power output terminal of the precharge module is connected to the power output terminal of the LDO via the isolation control module; The isolation control module is used to connect the power output terminal of the pre-charge module to the power output terminal of the LDO after the circuit is enabled and the output voltage of the LDO reaches a predetermined value; otherwise, it disconnects the power output terminal of the pre-charge module from the power output terminal of the LDO.

2. The separate power-on circuit for the pre-charge module and LDO according to claim 1, characterized in that, The isolation control module includes: The LDO establishment detection unit is used to detect whether the output voltage and enable signal of the LDO have reached the corresponding predetermined values, and outputs an indication signal; the enable signal is connected to the pre-charge module to control the activation and deactivation of the circuit. A controlled switch has a controlled terminal, a first connection terminal, and a second connection terminal. The controlled terminal is used to receive and control the connection and disconnection between the first connection terminal and the second connection terminal according to the indication signal. The first connection terminal is connected to the power output terminal of the pre-charge module, and the second connection terminal is connected to the power output terminal of the LDO.

3. The separate power-on circuit for the pre-charge module and LDO according to claim 2, characterized in that, The LDO-based detection unit includes: The AND gate receives an LDO setup status signal at its first input and an enable judgment signal at its second input; the enable judgment signal is obtained based on a comparison between the enable signal and a corresponding predetermined value. An inverter is used, and the output of the AND gate is connected to the output of the indicator signal via the inverter.

4. The separate power-on circuit for the pre-charge module and LDO according to claim 3, characterized in that, The LDO-based detection unit also includes: A first resistor (R1') is connected at one end to the output terminal of the inverter, and at the other end to the output terminal of the indicator signal. A first capacitor (C1') is connected at one end to the output terminal of the indicator signal, and the other end of the first capacitor (C1) is grounded.

5. The separate power-on circuit for the pre-charge module and LDO according to claim 2, characterized in that, The isolation control module also includes a second resistor (R2'); the two ends of the second resistor (R2') are respectively connected to the second connection terminal of the controlled switch and the power output terminal of the LDO.

6. The separate power-on circuit for the pre-charge module and LDO according to claim 2, characterized in that, The isolation control module also includes a second capacitor (C2'); the two ends of the second capacitor (C2') are respectively connected to the controlled end and the first connection end of the controlled switch.

7. The separate power-on circuit for the pre-charge module and LDO according to claim 2, characterized in that, The controlled switch is a MOS transistor; the gate of the MOS transistor is the controlled terminal, and the source and drain of the MOS transistor are the first connection terminal and the second connection terminal, respectively.

8. The separate power-on circuit for the pre-charge module and LDO according to claim 1, characterized in that, The power output terminal of the LDO is grounded via a third capacitor (C3').

9. The separate power-on circuit for the pre-charge module and LDO according to claim 1, characterized in that, It also includes a bias module, wherein the power output terminal of the precharge module is connected to the power input terminal of the bias module.

10. A chip comprising a precharge module and a separate power-on circuit for an LDO as described in any one of claims 1-9.

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