CN103199689B - A kind of Switching Power Supply with input voltage undervoltage lookout function - Google Patents

Abstract

The present invention relates to switching power source chip designing technique.The invention discloses a kind of Switching Power Supply with input voltage undervoltage lookout function, comprise the first NMOS tube, the second NMOS tube, the 3rd NMOS tube, the first electric capacity, the second electric capacity, the 3rd electric capacity, the 4th electric capacity, the first diode, the second diode, inductance and linear voltage regulator module, under-voltage locking module, upper pipe driver module and control module.Switching Power Supply of the present invention does not need comparator and reference voltage to realize input voltage under-voltage locking, reduce circuit complexity, because other high pressure resistant device realizes input voltage undervoltage lookout function in system for recycling, therefore save chip area and cost.

Description

A Switching Power Supply with Input Voltage Undervoltage Lockout Function

technical field

The invention relates to a switching power supply chip design technology, in particular to a switching power supply integrated circuit with an input voltage undervoltage locking function.

Background technique

In order to make the switching power supply chip work normally and stably, its input voltage must be within a certain range, so as to ensure that the chip can provide stable and reliable power to the application system. When the input voltage is lowered, each module inside the chip works near the minimum working voltage at a lower input voltage, which is very likely to cause abnormal internal functions, resulting in unstable power supply, and may even have a serious impact on the application system. Moreover, when the input voltage is powered by a battery, an over-low discharge voltage is likely to cause over-discharge, which seriously endangers the life of the battery. Therefore, in order to delay the battery life and ensure the normal operation of the switching power supply chip, in the switching power supply design, the input voltage undervoltage lockout circuit is required to monitor whether the input voltage is within the normal input voltage range, so that when the input voltage is lower than the allowable range, Cut off the power supply in time to provide protection for the power system and application system.

At present, in some switching power supply systems, the input voltage undervoltage lockout circuit is placed in the design of the peripheral circuit of the system. This design will inevitably increase the number and area of printed circuit board components, which is not conducive to reducing costs and improving integration. In order to improve system integration, the input voltage locking circuit is generally integrated in the chip now. For example, the under-voltage lockout circuit proposed by the document 'Power supply module design in the low power consumption application' by PAN H, WU X, CHEN H is a circuit structure integrated in the chip. The switching power supply using this kind of undervoltage lockout (UVLO) module usually also includes a linear voltage regulator module, an upper tube drive module, a control module, etc., and most of its circuit schemes use a comparator to compare the sampled power supply voltage and the reference voltage. Compare to determine whether it is undervoltage. The disadvantages of this type of circuit design scheme are that firstly, it is necessary to realize the reference circuit and comparator circuit, the circuit structure is complex, and the power consumption is large; Each device in the locking circuit is not broken down, which will increase chip area and cost.

Contents of the invention

The technical problem to be solved by the present invention is to provide a switching power supply with an input voltage under-voltage lockout function in view of the above-mentioned shortcomings of the prior art.

The technical solution adopted by the present invention is a switching power supply with an input voltage undervoltage lockout function, which is characterized in that it includes a first NMOS transistor, a second NMOS transistor, a third NMOS transistor, a first capacitor , the second capacitor, the third capacitor, the fourth capacitor, the first diode, the second diode, the inductor and the linear regulator module, the undervoltage lockout module, the upper tube drive module and the control module; the linear regulator One end of the module is connected to the external power supply voltage of the chip and the drain of the second NMOS transistor, and the other end is connected to the source of the first NMOS transistor, the positive pole of the first diode, the positive pole of the second diode, and the first pole of the control module. One end and one end of the third capacitor are all connected; the drain of the first NMOS transistor, the cathode of the second diode, one end of the second capacitor, and the first end of the undervoltage lockout module are all connected to the first end of the upper transistor drive module. One end is connected; the gate of the first NMOS transistor, the anode of the first diode are connected to one end of the first capacitor; the other end of the second capacitor, the second end of the undervoltage lockout module, and the The second end, the source of the second NMOS transistor, and the drain of the third NMOS transistor are all connected to one end of the inductor; the third end of the undervoltage lockout module is connected to the third end of the upper transistor drive module; the other end of the inductor One end is connected with one end of the fourth capacitor; the fourth end of the upper tube drive module is connected with the gate of the second NMOS transistor; the second end of the control module is connected with the fifth end of the upper tube drive module, and the third The terminal is connected with the gate of the third NMOS transistor and the other end of the first capacitor, and the fourth end, the source electrode of the third NMOS transistor, the other end of the third capacitor, and the other end of the fourth capacitor are all connected to the ground potential connect.

Further, the linear voltage regulator module is a low dropout linear voltage regulator module.

Specifically, the undervoltage lockout module has a hysteresis characteristic.

The beneficial effect of the present invention is that no comparator and reference voltage are needed to realize the input voltage under-voltage lockout, which reduces the circuit complexity, and because other high-voltage-resistant devices in the system are reused to realize the input voltage under-voltage lockout function, the chip area is saved and cost. In addition, the present invention also directly monitors the voltage difference of the upper tube drive module, thereby more timely avoiding the decrease of driving capability caused by insufficient voltage difference and a series of serious problems caused thereby.

Description of drawings

Fig. 1 schematic diagram of circuit structure of the present invention;

Figure 2 is a normal timing diagram of key signals;

Fig. 3, Fig. 4 and Fig. 5 are the equivalent circuit diagrams of the switching power supply of the present invention under different modes;

Figure 6 is a timing diagram of key signal exceptions.

In the figure: M1, M2, and M3 are NMOS transistors (N-type metal oxide semiconductor field effect transistors), where M2 is connected to the power supply and is called the upper transistor, and M3 is grounded and called the lower transistor; C1, C2, C3, and COUT are capacitors; D1, D2, and D3 are diodes, among which D3 is the body diode of M3 or called parasitic diode; L is the inductor; LVR is the linear voltage regulator module; UVLO is the undervoltage lockout module; HDR is the upper tube drive module; CTRL is the control module.

Detailed ways

The technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Aiming at the existing problems of the input voltage undervoltage lockout circuit in the existing switching power supply system, such as complex structure, many devices and large area, the present invention proposes a switching power supply with the function of input voltage undervoltage lockout, the specific circuit structure is as follows As shown in Figure 1, it includes NMOS transistors M1, M2, M3, capacitors C1, C2, C3, COUT, diodes D1, D2, inductor L, linear voltage regulator module LVR, undervoltage lockout module UVLO, upper tube drive module HDR and Control module CTRL. The specific connection relationship is as follows:

The power input terminal of the linear voltage regulator module LVR is connected with the chip external input power supply voltage VIN and the drain of the NMOS transistor M2, and its output terminal VDD is connected with the source of the NMOS transistor M1, the anode of the diode D1, the anode of the diode D2, and the control The first terminal of the module CTRL is connected to one terminal of the capacitor C2. The drain of the NMOS transistor M1, the cathode of the diode D2, one end of the capacitor C2, and the first end of the undervoltage lockout module UVLO are all connected to the first end of the upper tube drive module HDR; the gate of the NMOS transistor M1 is connected to the capacitor C1 One end is connected to the cathode of the diode D1. The other end of the capacitor C2, the second end of the undervoltage lockout module UVLO, the second end of the high-side driver module HDR, the source of the NMOS transistor M2, and the drain of the NMOS transistor M3 are all connected to one end of the inductor L. The third terminal of the undervoltage lockout module UVLO is connected with the third terminal of the high tube drive module HDR. The other end of the inductor L is connected to one end of the capacitor COUT. The fourth terminal of the high-side transistor driving module HDR is connected to the gate of the NMOS transistor M2. The second end of the control module CTRL is connected to the fifth end of the upper tube drive module HDR, the third end of the control module CTRL is connected to the gate of the NMOS transistor M3 and the other end of the capacitor C1, and the fourth end of the control module CTRL And the source of the NMOS transistor M3, the other end of the capacitor C3, and the other end of the capacitor COUT are all connected to the ground potential.

Among them, the linear voltage regulator module LVR includes a low-dropout linear voltage regulator (LDO), etc., also known as a low-dropout linear voltage regulator module. Its main function is to provide a safe and stable working voltage for each circuit module inside the chip, as shown in Figure 1 Only the input terminal VIN and the output terminal VDD of the power supply are shown, and other signals such as the enable control signal, reference voltage, bias current, and ground potential are omitted. The capacitor C3 is the filter capacitor of the LVR, and the diode D1 and the capacitor C1 form a local bootstrap circuit to drive the NMOS transistor M1. The NMOS transistor M1, the diode D2 and the capacitor C2 form a bootstrap circuit to keep a constant voltage difference between the BST node and the SW node, and provide a floating power rail for the upper transistor drive module HDR to drive the NMOS transistor M2. The undervoltage lockout module, UVLO, detects undervoltage on the floating rail without requiring an external voltage or current reference. The control module CTRL includes functions such as loop comparison, output voltage overvoltage, undervoltage protection, output current protection, and logic processing. The dotted line in Figure 1 indicates the feedback current signal or voltage signal, and FB is the feedback signal connection terminal of the control module CTRL. NMOS tubes M2, M3, inductor L and output capacitor COUT form the basic topology of the switching power supply, and other bias circuits are not marked.

In the following, the working principle of the switching power supply of the present invention will be described with respect to the different switching states of the NMOS transistors M2 and M3 in one cycle.

1. NMOS tube M2 is turned off, and NMOS tube M3 is turned on:

As shown in FIG. 2 , when the output control signals HSG and LSG of the control module CTRL are in the state before time T1 , the NMOS transistor M2 in FIG. 1 is turned off, the NMOS transistor M3 is turned on, and the NMOS transistor M1 is also turned on. At this time, if the turn-on voltage drop on the NMOS transistor M1 and the NMOS transistor M3 is ignored, the circuit in FIG. 1 can be equivalent to the circuit shown in FIG. 3 . As can be seen from Figure 3, at this time SW is connected to ground potential, BST node is connected to VDD, and VDD charges capacitor C2 to increase the voltage difference between BST node and SW node. Assuming enough time, BST node and SW The voltage difference between the nodes will be equal to the voltage difference between VDD and ground. It is worth noting that even if the undervoltage lockout module UVLO is triggered within this time period, it will not affect the system.

2. NMOS tubes M2 and M3 are turned off at the same time for the first time:

As shown in Figure 2, when the output control signals HSG and LSG of the control module CTRL are in the state between time T1 and T2, the NMOS transistors M2 and M3 in Figure 1 are turned off at the same time for the first time, and the NMOS transistor M1 is also turned off. The freewheeling characteristics of the SW node drop to a negative potential (about the forward conduction voltage drop of the body diode D3), so that the body diode of the NMOS transistor M3 is forced to open for the freewheeling of the inductor L, then the circuit in Figure 1 can be equivalent to 4 shows the circuit. It can be seen from Figure 4 that at this time, the SW node is connected to the ground potential through the body diode D3 of the NMOS transistor M3, and the BST node is connected to VDD through the diode D2. Since the upper tube drive module circuit HDR does not flip at this stage, the BST The node and SW node still maintain the original constant voltage, but they are no longer equal to VDD and ground potential, but are VDD-VD and -VD respectively (assuming that the forward conduction voltage drop of diode D2 and body diode D3 of M3 is equal). It is worth noting that if the undervoltage lockout module UVLO is triggered during this period, it will not have an immediate impact on the system, but whether the input voltage is undervoltage at the end of this period determines whether the input voltage undervoltage protection function is triggered.

A. If there is no undervoltage at the end of this stage or the undervoltage is released in time, then in the next stage (time T2-T3), each driving signal will be reversed normally, NMOS transistor M2 will be turned on, and NMOS transistor M3 will be turned off. If the NMOS transistor is ignored The conduction voltage drop on the tube M2, the SW node is connected to VIN, and VIN transmits current to the inductor L through the NMOS tube M2, the circuit in Figure 1 can be equivalent to the circuit shown in Figure 5.

B. If the undervoltage is not released at the end of this stage, then in the next stage (time T2-T3), the HSG signal is shielded by the undervoltage signal output by the undervoltage lockout module UVLO, and the drive signal output by the upper tube drive module HDR does not Inverting, the NMOS transistors M2 and M3 continue to be turned off, and the circuit shown in FIG. 1 can still be equivalent to the circuit shown in FIG. 4 . Assuming that the switching power supply is in continuous conduction mode, the SW node waveform diagram is shown in Figure 6. Until the next cycle when the NMOS transistor M1 is turned on, VDD charges the capacitor C1 so that the voltage difference between the BST node and the SW node is higher than the UVLO threshold of the undervoltage lockout module before the lock can be released. If it is still not released after several cycles, the capacitor COUT will continue to be unable to receive energy replenishment, and eventually the voltage of the VOUT node will drop to a certain value, triggering the chip output voltage undervoltage protection module, and the chip will stop working.

It is worth noting that the undervoltage lockout module UVLO directly monitors the voltage difference of the floating power supply of the upper tube drive module circuit HDR during the above undervoltage lockout process, so that the insufficient driving capability caused by insufficient voltage difference can be avoided in a timely manner. And a series of serious problems brought thereby, Here it is another beneficial effect of the present invention.

Assuming that the undervoltage lockout module UVLO has hysteresis characteristics, set its trigger lock threshold voltage as V _LOCK , unlock its threshold voltage as V _UNLOCK , and the voltage difference between the input voltage VIN and output voltage VDD of the linear voltage regulator module LVR as V _DROP (For linear regulators, V _DROP does not vary much when VIN is low), then the following conclusions can be drawn:

(1) The trigger threshold voltage of the input voltage undervoltage lockout can be expressed as VIN _LOCK =V _LOCK +V _DROP ;

(2) The release threshold voltage of the input voltage under-voltage lockout can be expressed as VIN _UNLOCK =V _UNLOCK +V _DROP .

It can be seen that the input voltage undervoltage threshold (VIN _LOCK and VIN _UNLOCK ) can be set by adjusting the UVLO threshold voltage (V _LOCK and V _UNLOCK )

In summary, the switching power supply with input voltage undervoltage lockout function of the present invention realizes the input voltage undervoltage lockout function ingeniously by virtue of the withstand voltage device in the linear adjustment module, the structural characteristics of the bootstrap circuit and the switching device of the switching power supply.

It should be noted:

1. Since the focus of the present invention is to propose a switching power supply structure with an input voltage under-voltage lockout function, the implementation of the UVLO internal circuit will not be described in detail.

2. The undervoltage lockout module UVLO may or may not have a hysteresis characteristic, both of which are applicable to the switching power supply of the present invention.

3. The schematic diagram and expression of the switching power supply in the present invention only include modules closely related to the present invention, and do not mention or identify other modules or circuit details that are not related to the expression of the present invention.

The above content has carried out a detailed introduction to the switching power supply of the present invention, and explained the principles and implementation modes of the present invention. The above examples are only used to help understand the basic principles and core ideas of the present invention. Changes made to specific implementation methods above the core idea should all fall within the scope of the present invention.

Claims (1)

1. one kind has the Switching Power Supply of input voltage undervoltage lookout function, it is characterized in that, comprise the first NMOS tube, the second NMOS tube, the 3rd NMOS tube, the first electric capacity, the second electric capacity, the 3rd electric capacity, the 4th electric capacity, the first diode, the second diode, inductance and linear voltage regulator module, under-voltage locking module, upper pipe driver module and control module; One end of linear voltage regulator module is connected with the drain electrode of chip exterior supply voltage with the second NMOS tube, and one end of the source electrode of the other end and the first NMOS tube, the positive pole of the first diode, the positive pole of the second diode, the first end of control module and the 3rd electric capacity is all connected; One end of the drain electrode of the first NMOS tube, the negative pole of the second diode, the second electric capacity, the first end of under-voltage locking module are all connected with the first end of upper pipe driver module; The grid of the first NMOS tube, the positive pole of the first diode are connected with one end of the first electric capacity; The drain electrode of the second end of the other end of the second electric capacity, the second end of under-voltage locking module, upper pipe driver module, the source electrode of the second NMOS tube, the 3rd NMOS tube is all connected with one end of inductance; 3rd end of under-voltage locking module is connected with the 3rd end of upper pipe driver module; The other end of inductance is connected with one end of the 4th electric capacity; 4th end of upper pipe driver module is connected with the grid of the second NMOS tube; Second end of control module is connected with the five terminal of upper pipe driver module, its the 3rd end is connected with the grid of the 3rd NMOS tube and the other end of the first electric capacity, and the other end of the source electrode of its 4th end and the 3rd NMOS tube, the other end of the 3rd electric capacity, the 4th electric capacity is all connected with earth potential;

Described linear voltage regulator module is low pressure difference linear voltage regulator module;

Described under-voltage locking module has hysteretic characteristic.