TW201822425A - Lithium battery control circuit and lithium battery charger - Google Patents

Abstract

A lithium battery control circuit and a lithium battery charger are provided. The lithium battery charger includes the lithium battery control circuit. The lithium battery control circuit includes a smooth transition circuit and an off-time control circuit. The smooth transition circuit generates a first voltage according to a sense current signal and a feedback signal, and a second voltage according to a mode signal. The smooth transition circuit compares the first voltages with the second voltages to generate a reset signal. The off-time control circuit converts the feedback signal to generate a first current by a voltage to current mechanism, and generates a set signal by using the first current and a duty ratio signal. The present invention can prevent a surge current and an oscillation phenomenon by the smooth transition circuit. A switching frequency and a ripple size of an output current are controlled by the off-time control circuit.

Description

Lithium battery control circuit and lithium battery charger

The present invention relates to a charging technology for a lithium battery, and more particularly to a lithium battery control circuit and a lithium battery charger that can improve the efficiency of the overall charger.

FIG. 1A is an equivalent circuit diagram of a conventional lithium battery charging. For the actual lithium battery 100, the internal resistance Rbir is not a constant but a variable value. The reason is that the internal resistance Rbir is changed by the influence of the dependent temperature, the charging current Ich, the number of times of use, and the like.

FIG. 1B is a schematic diagram showing the correlation between internal resistance and current of a lithium battery. Whether in the case of charging or discharging, the internal resistance Rbir of the lithium battery will have a large resistance value for a large charging current or discharging current.

1C is a schematic diagram showing the correlation between the internal resistance of a lithium battery and the battery capacity. Whether in the case of charging or discharging, and when the lithium battery is at a lower percentage capacity or a higher percentage capacity, the internal resistance Rbir of the lithium battery will also have a larger resistance value.

In general, when charging a lithium battery, various types of charging modes may be experienced. For example, a trickle current (TC) mode, a constant current (CC) mode, and a constant voltage (CV) mode. 2A is a schematic diagram of a charging process from a small current mode to a constant current mode. 2B is a schematic diagram of a charging process from a constant current mode to a constant voltage mode. When another type of charging mode is switched (or entered) by a certain type of charging mode, a surge current is generated on the circuit to oscillate, as indicated by the dashed circle 210 of FIG. 2A or the dashed circle 220 of FIG. 2B.

During the charging process, the cause of the surge current may be analyzed as follows. In FIG. 1A, when the charger 120 detects that the battery voltage VB is sufficiently high and before entering the constant voltage mode from the constant current mode, the lithium battery 100 corresponds to a larger charging current and a higher battery capacity, respectively. 1B is shown in Figure 1C. The internal resistance Rbir in this case will be large relative to the case of a smaller charging current and a lower battery capacity. Based on the large current and large resistance values, there will be a significant voltage drop across the internal resistor Rbir. When the charger 120 enters the constant voltage mode, the charging current Ich becomes small, and the internal resistance Rbir of the lithium battery 100 also decreases relatively, which causes the voltage drop to become instantaneously small, and causes the charger 120 to misjudge that the battery voltage VB is insufficient, so The constant voltage mode is switched to the constant current mode to operate. However, the voltage drop will rise again, and the charger 120 enters the constant voltage mode again until the voltage of the lithium battery 100 reaches a preset value, and the oscillation is stopped.

In the case of a general lithium battery buck charger, when the charging operation is in the second half (such as constant voltage mode), the buck converter in the circuit architecture appears as a voltage mode buck converter, so the buck charger The output will present two overlapping poles. In order to prevent the oscillation of the system, the conventional technology adopts a complicated design compensation circuit to solve the stability problem, thereby increasing the development time and cost.

Since the compensation circuit for the charger is quite complicated, the compensation circuit takes up a considerable amount of circuit area. Based on the overall circuit of the charger and the safety of the battery, it should also have a circuit or mechanism to prevent the generation of surge current.

- The present invention proposes a lithium battery control circuit and a lithium battery charger to solve the problems described in the prior art.

The invention provides a lithium battery control circuit. The lithium battery control circuit includes a smoothing conversion circuit and a shutdown time control circuit. The smoothing conversion circuit generates a first voltage according to the sensing current signal and the feedback signal, and generates a second voltage according to the mode signal, and compares the first voltage with the second voltage to generate a reset signal. The sense current signal is related to the output current. The feedback signal is related to the output voltage. The mode signal is used to indicate whether it is in the first charging mode, and the second voltage in the first charging mode is less than the second voltage in the non-first charging mode. The off time control circuit converts the feedback signal by a voltage conversion current mechanism to generate a first current, and uses the first current and the duty ratio signal to generate a set signal.

The invention provides a lithium battery charger. The lithium battery charger includes a lithium battery control circuit, a current sensing circuit, and a feedback circuit. The lithium battery control circuit includes: a smooth conversion circuit, generating a first voltage according to the sensing current signal and the feedback signal, generating a second voltage according to the mode signal, and comparing the first voltage with the second voltage to generate a reset signal, Wherein the feedback signal is related to the output voltage, the mode signal is used to indicate whether it is in the first charging mode, and the second voltage in the first charging mode is less than the second voltage in the non-first charging mode; and the closing time The control circuit converts the feedback signal by a voltage conversion current mechanism to generate a first current, and uses the first current and the duty ratio signal to generate a setting signal; and the current sensing circuit generates the sensing according to the output current a current signal; and a feedback circuit for generating a feedback signal based on the output voltage.

Based on the above, the lithium battery control circuit and the lithium battery charger of the present invention employ a smooth conversion circuit in combination with a shutdown time control circuit. The surge current and the oscillation phenomenon are prevented by the smooth conversion circuit during the conversion of each charging mode, and the switching frequency and the chopping size of the output current can be controlled by turning off the time control circuit, thereby improving the efficiency of the overall charger. The lithium battery control circuit and the lithium battery charger of the present invention do not need to configure a complicated compensation circuit in the path of the feedback circuit, and the structure is simple. On the other hand, the present invention can reduce the complexity of the charger and reduce the manufacturing cost as compared with the conventional charger, and is in line with the development trend of the current consumer electronic products.

In the embodiments described below, when an element is referred to as "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there may be intervening elements. The term "circuitry" can be used to mean at least one element or elements, or elements that are actively and/or passively coupled together to provide suitable functionality. It should be understood that the physical characteristics of the signals referred to in this specification and the drawings may be voltage or current.

Please refer to Figure 3. The lithium battery charger 300 can be used to charge the lithium battery 390. The lithium battery charger 300 can include a lithium battery control circuit 310, a current sensing circuit 350, a feedback circuit 360, a drive circuit 370, and an output stage 380. Hereinafter, the overall circuit composed of the lithium battery charger 300 and the lithium battery 390 will be referred to by "charging system" or "system".

The lithium battery control circuit 310 may include a smoothing conversion circuit 320, an off time control circuit 330, and a logic control circuit 340. The current sensing circuit 350 can include an inductor L, a resistor Rsen, and a comparator A1. The current sensing circuit 350 can sense the output current I _L flowing through the inductor _L and generate a sensing current signal Isen according to the output current I _L . As long as the current sensing circuit 350 can generate the sensing current signal Isen according to the output current I _L . The feedback circuit 360 can include a resistor Rf1 and a resistor Rf2, or can include a resistor network or a resistor-capacitor network. As long as the feedback circuit 360 can generate the feedback signal FB according to the output voltage Vout.

The following will describe the prevention of the surge current and the oscillation phenomenon by the smoothing conversion circuit 320, and the switching frequency and the chopping size of the output current I _L by turning off the time control circuit 330.

Please refer to Figure 3 and Figure 4. The smoothing conversion circuit 320 may include a current source 410, a P-type metal oxide semiconductor (PMOS) transistor 412, a PMOS transistor 414, a PMOS transistor 416, a comparator 418, and a resistor 420.

The detailed component coupling relationship is as follows. The current source 410 is related to the sensed current signal Isen, which exhibits a linear proportional relationship. A first end (eg, a source) of the PMOS transistor 412 is coupled to the first end of the current source 410, and a second end (eg, a drain) of the PMOS transistor 412 is coupled to the control terminal (eg, the gate) The second end of source 410. The first end of the PMOS transistor 414 is coupled to the first end of the current source 410 and the first end of the PMOS transistor 412. The control end of the PMOS transistor 414 is coupled to the control end of the PMOS transistor 412. A first input (eg, a positive input) of comparator 418 receives a reference voltage Vrefv, and a second input (eg, a negative input) of comparator 418 receives a feedback signal FB.

The first end of the PMOS transistor 416 is coupled to the first end of the PMOS transistor 414, the second end of the PMOS transistor 416 is coupled to the second end of the PMOS transistor 414, and the control end of the PMOS transistor 416 is coupled to the comparator 418. The output. The first end of the resistor 420 is coupled to the second end of the PMOS transistor 414 and the second end of the PMOS transistor 416, and the second end of the resistor 420 is coupled to the ground GND. A first voltage Vmix is generated at a first end of the resistor 420.

The smoothing conversion circuit 320 may further include a PMOS transistor 422, a resistor 424, a PMOS transistor 426, a current source 428, a switch 430, and a resistor 432.

The detailed component coupling relationship is as follows. The first end of the resistor 424 is coupled to the second end of the PMOS transistor 422, and the second end of the resistor 424 is coupled to the ground GND. The first end of the PMOS transistor 426 is coupled to the first end of the PMOS transistor 422, and the control end of the PMOS transistor 426 is coupled to the control terminal of the PMOS transistor 422. The first end of the current source 428 is coupled to the second end of the PMOS transistor 426, and the second end of the current source 428 is coupled to the ground GND. The control terminal of the switch 430 receives the mode signal CCF, and the first end of the switch 430 is coupled to the first end of the resistor 424. The first end of the resistor 432 is coupled to the second end of the switch 430, and the second end of the resistor 432 is coupled to the ground GND. A second voltage Vrefi is generated at the first end of the resistor 424.

As shown in FIG. 3, the mode selection circuit 400 can generate the mode signal CCF according to the output voltage Vout. For example, when the mode selection circuit 400 determines that the output voltage Vout is less than the predetermined voltage, the mode signal CCF is indicated as the first charging mode.

In the embodiment, the smoothing conversion circuit 320 can generate the first voltage Vmix according to the sensing current signal Isen and the feedback signal FB, and can generate the second voltage Vrefi according to the mode signal CCF, and compare by the comparator 434. The first voltage Vmix and the second voltage Vrefi generate a reset signal Sres.

Current source 428 is used to cause PMOS transistor 422 to generate current Irefi. When the mode signal CCF indicates the first charging mode (eg, the output voltage Vout is less than 2.65V, but not limited thereto), the switch 430 causes the resistor 424 to be connected in parallel with the resistor 432, and the equivalent resistance value will be compared to the resistor 424. Or the resistance value of the resistor 432 is smaller, so the equivalent resistance value and the current Irefi can be used to generate the second voltage Vrefi, thereby controlling the reset signal Sres and achieving a small current.

In addition, for the charging operation of the lithium battery, various types of charging modes can be employed. .

When the mode signal CCF indicates a non-first charging mode, then the switch 430 causes the resistor 432 to be non-conducting such that the equivalent resistance value will be equal to the resistor 424. In this way, the equivalent resistance value and the current Irefi will produce a second voltage Vrefi which is higher than the parallel mode, and the charging mode will also have a larger charging current. More specifically, the first charging mode may be a low current mode, and the non-first charging mode may be a constant current mode or a constant voltage mode.

In the final charging process (ie, in the second half of the charging operation), the constant voltage mode will be entered into the constant voltage mode. Please refer to Figure 3 to Figure 5 together. In the constant current mode, since the output voltage Vout does not reach the preset value (for example, the preset value can be 4.2V, but not limited to this), the feedback signal FB will be a smaller voltage value, and the voltage loop gain It will not be big enough. The current signal Ivmix flowing out at the first voltage Vmix has only information from the sense current signal Isen. When the output voltage Vout approaches a preset value, the voltage loop gain via the feedback circuit 360 will be sufficiently large, and the feedback signal FB causes the voltage signal Vsignal to be slowly injected into the first voltage Vmix and the current signal Ivmix The mixing, and thus the mixed signal shown by dashed circle 510, can be used to control the change in output current I _L . In addition, the effect shown by the dashed rectangle 520 is a smoothed output current I _L . Therefore, the smoothing conversion circuit 320 can be used for the purpose of constant voltage charging and for achieving the purpose of mixing both voltage and current signals.

Please refer to Figure 3, Figure 4 and Figure 6. In FIG. 6, when the charging operation is in the constant current mode, since the output voltage Vout from the output terminal is not large enough, the loop gain is insufficient to cause the voltage signal Vsignal to be zero, and there is no influence on the control of the charging system. The lithium battery charger 300 only locks the current for the sensing current signal Isen from the current sensing circuit 350, and the current signal Ivmix flowing out at the first voltage Vmix has only information from the sensing current signal Isen. The comparator 434 compares the current signal Ivmix with the second voltage Vrefi for peak current control locking, thereby locking the output to a constant current for the purpose.

In addition, when the output voltage Vout approaches the nominal value, the voltage signal Vsignal will begin to be added to the system, and the equivalent of the signal analysis is to raise the sense current signal Isen to synthesize the current signal Ivmix. The peak current control can be performed by both the current signal Ivmix and the second voltage Vrefi, thereby locking the voltage at the output. As such, the lithium battery control circuit 310 has the advantage of preventing a surge current from occurring.

In addition, the effect shown by the dashed circle 610 is smooth. The control of the lithium battery control circuit 310 simultaneously uses signals of both voltage and current, so the system operates like a current mode buck converter. The overall system can be simplified to a single pole system in terms of stability analysis, thus having the effect of simplifying the compensation circuit of the charger.

Further, the smoothing conversion circuit 320 can operate in conjunction with the off-time control circuit 330 described below, and can also have the effect of simplifying the compensation circuit of the charger in the configuration of the system.

Please refer to Figure 3 and Figure 7. The off time control circuit 330 can include a PMOS transistor 710, a PMOS transistor 712, an N-type metal oxide semiconductor (NMOS) transistor 714, a resistor 716, a comparator 718, a capacitor 720, an NMOS transistor 722, and a comparator 724.

The detailed component coupling relationship is as follows. The first end of the PMOS transistor 712 is coupled to the first end of the PMOS transistor 710, and the control end of the PMOS transistor 712 is coupled to the second end of the PMOS transistor 710 and the control terminal. The first end (eg, the drain) of the NMOS transistor 714 is coupled to the second end of the PMOS transistor 710 and the control terminal. The first end of the resistor 716 is coupled to the second end (eg, the source) of the NMOS transistor 714, and the second end of the resistor 716 is coupled to the ground GND. The first input (eg, the positive input) of the comparator 718 receives the feedback signal FB, and the second input (eg, the negative input) of the comparator 718 is coupled to the first end of the resistor 716 and the NMOS transistor 714. The second end of the comparator 718 is coupled to the control terminal (eg, the gate) of the NMOS transistor 714.

The first end of the capacitor 720 is coupled to the second end of the PMOS transistor 712, and the second end of the capacitor 720 is coupled to the ground GND. The first end of the NMOS transistor 722 is coupled to the first end of the capacitor 720, the second end of the NMOS transistor 722 is coupled to the ground GND, and the control end of the NMOS transistor 722 receives the duty ratio signal Sduty. A first input (eg, a positive input) of the comparator 724 is coupled to a second end of the PMOS transistor 712 and a first end of the capacitor 720, and a second input (eg, a negative input) of the comparator 724 receives the reference The voltage REF, the output of the comparator 724 outputs a set signal Sset.

Note that the current ratio through PMOS transistor 710 to PMOS transistor 712 is N:1, where the current through PMOS transistor 712 is defined as first current 726, and N is a positive number.

Further, the configuration of the comparator 718, the PMOS transistor 710, the PMOS transistor 712, and the NMOS transistor 714 can be used as a mechanism for voltage conversion current. The off time control circuit 330 converts the feedback signal FB by the mechanism of the voltage conversion current to generate a first current 726. The off time control circuit 330 can further generate the set signal Sset using the first current 726 and the duty ratio signal Sduty.

Further, the logic control circuit 340 in FIG. 3 may be an SR flip-flop, but the present invention is not limited thereto. For example, the S terminal of the logic control circuit 340 is coupled to the output of the shutdown time control circuit 330, and the R terminal of the logic control circuit 340 is coupled to the output of the smoothing conversion circuit 320. The Q terminal of the logic control circuit 340 can generate a duty ratio signal Sduty for pulse frequency modulation according to the received reset signal Sres and the set signal Sset, and output the duty ratio signal Sduty to the drive circuit 370. The drive circuit 370 can operate the output stage 380 in accordance with the duty ratio signal Sduty. The lithium battery charger 300 can perform the frequency conversion operation by using the duty ratio signal Sduty, thereby enabling the system to avoid subharmonic oscillations.

Further, the off time control circuit 330 is the core of the entire charger. The off time control circuit 330 is responsible for adjusting the length of the off-time and suppressing the output chopping from becoming large. The off time control circuit 330 controls the length of the off time using the feedback signal FB related to the output voltage Vout. In this way, the lithium battery control circuit 310 can control the switching frequency of the output current I _L and the chop size.

In addition, the shutdown time control circuit 330 can use a single periodicity of "off-time control" to eliminate subharmonic oscillation effects of current in the current mode buck.

On the other hand, since the output voltage Vout of the charger will continuously rise during the charging process, if the mechanism of the fixed off time in the prior art is employed, the problem that the output current chopping constantly becomes large will surely occur. For example, waveform 810 shown in FIG. 8 is related to output current I _L , and each of the waveforms 810 exhibits a fixed off time. In the architectural characteristics of the buck converter, the "off-time" discharge slope is proportional to the output voltage, as shown in Equation 1 below.

The off time slope = -Vout/L, where Vout represents the output voltage value and L represents the inductance value (Equation 1).

If the turn-off time is a fixed constant and is based on the architectural characteristics of the buck converter, the higher the output voltage, the greater the relative slope and will cause the output current to ripple more and more. Therefore, it is necessary to linearly control and adjust the length of the off time by the feedback signal as in the present invention, and suppress the output current to make the charging efficiency of the system better.

As shown in Fig. 7, in the present embodiment, a feedback signal FB and a voltage (V) to current (I) circuit are used to generate a voltage-dependent current. The current associated with the voltage-dependent current is scaled at a suitable linear ratio (eg, N: 1) to charge capacitor 720, and the length of this charging time is defined as the off time.

The off time control circuit 330 can operate in conjunction with the smoothing conversion circuit 320 described above. In the present embodiment, the NMOS transistor 722 uses the duty ratio signal Sduty to control the path for discharging. The comparator 724 uses the reference voltage REF as the upper limit of the charging voltage. The invention can define the closing time by charging and discharging of the capacitor 720, thereby controlling the switching frequency of the system.

The way the voltage is converted to current is a linear conversion/scaling. When the characteristics of the capacitor current are used, a turn-off time linearly related to the output voltage can be obtained, as shown in Equations 2 and 3 below.

And Where C represents the capacitance value of capacitor 720, Ic represents the current value flowing through capacitor 720, Vc represents the voltage value across capacitor 720, FB represents the value of the feedback signal, and Rf represents the resistance value of resistor 716. 2).

Closing time (Formula 3).

Closing time slope = And chopping = Where Vout represents the value of the output voltage and L represents the inductance value (Equation 4).

If FB= And Vc=REF, where k is a coefficient or constant parameter, and REF represents a value of the reference voltage (Equation 5).

Closing time (Formula 6).

涟波= (Formula 7).

涟波= ,among them , Is the coefficient or constant parameter (Equation 8).

The feedback signal FB is related to the magnitude of the output voltage Vout. When the output voltage Vout is higher, the appropriately scaled current 726 is also increased, and the relative charging time is shortened, which is equivalent to shortening the circuit closing time.

From the derivation of Equations 4 to 8, it can be seen that the parameter value proportional to the output voltage Vout in the output chopping equation can be offset by the introduced feedback signal FB related to the output voltage. Therefore, when there is only a constant parameter in the equation and there is no function of the output voltage, the output current chopping will not become larger as the output voltage rises, and the output current ripple can be improved or reduced.

In consideration of system performance, the present invention can be applied to a wafer, and the method of current sensing and peak current control is used to replace the general sensing resistance and the average current, thereby improving the disadvantages of the prior art in efficiency. It can also improve the efficiency of the overall charger.

In addition, the peak current control method can be applied to the chopping problem encountered in the switched charging circuit, and can also be used in the chopping control off time control circuit to solve the chopping problem.

Considering the stability and safety of the system, the smooth conversion circuit combined with the smooth conversion and peak current control can successfully prevent the oscillation of the charging mode during the conversion and the non-ideal surge current on the charger operation. The charging operation of the charger of the present invention also includes a current mode and simplifies the complicated compensation circuit of a general switched charger.

Based on the disclosure of the above embodiments, the lithium battery charger of the present invention has a smooth transition circuit architecture in current mode. The design of the lithium battery charger of the present invention is improved for high performance, high stability, low cost, and low complexity, and uses peak current control, and uses both off-time control and current mode to operate together.

The present invention not only solves the problem of chopping and surge currents, but also effectively protects the battery and extends battery life.

The system of the present invention integrates three characteristics of simplified compensation, protection circuitry, and system architecture in a smooth conversion circuit. The invention indirectly reduces the complexity of the switching charger, reduces the manufacturing cost, and conforms to the development trend of the current consumer electronics (3C) products.

In summary, the lithium battery control circuit and the lithium battery charger of the present invention can prevent the surge current and the oscillation phenomenon by the smooth conversion circuit. Moreover, the lithium battery control circuit and the lithium battery charger of the present invention can control the switching frequency and the chopping size of the output current by turning off the time control circuit.

100‧‧‧Lithium battery

120‧‧‧Charger

210‧‧‧dotted circle

220‧‧‧dotted circle

300‧‧‧Lithium battery charger

310‧‧‧Lithium battery control circuit

320‧‧‧Smooth conversion circuit

330‧‧‧Close time control circuit

340‧‧‧Logic Control Circuit

350‧‧‧ Current sensing circuit

360‧‧‧Return circuit

370‧‧‧ drive circuit

380‧‧‧Output

390‧‧‧Lithium battery

400‧‧‧ mode selection circuit

410‧‧‧current source

412‧‧‧ PMOS transistor

414‧‧‧ PMOS transistor

416‧‧‧ PMOS transistor

418‧‧‧ comparator

420‧‧‧Resistors

422‧‧‧ PMOS transistor

424‧‧‧Resistors

426‧‧‧ PMOS transistor

428‧‧‧current source

430‧‧‧ switch

432‧‧‧Resistors

434‧‧‧ comparator

510‧‧‧dotted circle

520‧‧‧dotted rectangle

610‧‧‧dotted circle

710‧‧‧ PMOS transistor

712‧‧‧ PMOS transistor

714‧‧‧NMOS transistor

716‧‧‧Resistors

718‧‧‧ comparator

720‧‧‧ capacitor

722‧‧‧NMOS transistor

724‧‧‧ Comparator

810‧‧‧ waveform

A1‧‧‧ comparator

CCF‧‧‧ mode signal

FB‧‧‧ feedback signal

GND‧‧‧ ground terminal

Ich‧‧‧Charging current

I _L ‧‧‧Output current

Irefi‧‧‧ Current

Isen‧‧‧ sense current signal

Ivmix‧‧‧ current signal

L‧‧‧Inductors

Rbir‧‧‧ internal resistance

REF‧‧‧reference voltage

Rf1‧‧‧Resistors

Rf2‧‧‧Resistors

Rsen‧‧‧Resistors

Sres‧‧‧Reset signal

Sset‧‧‧ setting signal

Sduty‧‧‧ work ratio signal

VB‧‧‧ battery voltage

Vmix‧‧‧ first voltage

Vout‧‧‧ output voltage

Vrefv‧‧‧reference voltage

Vrefi‧‧‧second voltage

Vsignal‧‧‧ voltage signal

FIG. 1A is an equivalent circuit diagram of a conventional lithium battery charging. FIG. 1B is a schematic diagram showing the correlation between internal resistance and current of a lithium battery. 1C is a schematic diagram showing the correlation between the internal resistance of a lithium battery and the battery capacity. 2A is a schematic diagram of a charging process from a small current mode to a constant current mode. 2B is a schematic diagram of a charging process from a constant current mode to a constant voltage mode. 3 is a schematic diagram of a lithium battery charger in accordance with an embodiment of the present invention. 4 is a circuit diagram of a smoothing conversion circuit in accordance with an embodiment of the present invention. 5 is a waveform diagram of a constant current mode to a constant voltage mode in accordance with an embodiment of the present invention. 6 is another waveform diagram of a constant current mode to a constant voltage mode in accordance with an embodiment of the present invention. 7 is a circuit diagram of a shutdown time control circuit in accordance with an embodiment of the present invention. Figure 8 is a waveform diagram of a conventional fixed off time.

Claims (12)

A lithium battery control circuit is suitable for control in a lithium battery charger, receiving a sensing current signal from a current sensing circuit, a feedback signal from a feedback circuit, and a duty ratio signal from a logic control circuit The method includes: a smoothing conversion circuit, generating a first voltage according to the sensing current signal and the feedback signal, and generating a second voltage according to a mode signal, and comparing the first voltage with the second voltage Generating a reset signal, wherein the sense current signal is related to an output current, the feedback signal is related to an output voltage, the mode signal is used to indicate whether it is in a first charging mode, and in the first charging mode The second voltage is less than the second voltage in the non-first charging mode; and a shutdown time control circuit converts the feedback signal by a voltage conversion current mechanism to generate a first current, and uses the The first current and the duty ratio signal generate a set signal. The lithium battery control circuit of claim 1, wherein the smoothing conversion circuit comprises: a first current source associated with the sensing current signal; a first PMOS transistor, the first PMOS transistor A first end of the first current source is coupled to a first end of the first current source, and a second end of the first PMOS transistor is coupled to a second end of the first current source; a second PMOS a first end of the second PMOS transistor is coupled to the first end of the first current source and a first end of the first PMOS transistor, and a control terminal of the second PMOS transistor is coupled The first comparator receives a first reference voltage, and a second input of the first comparator receives the back a third PMOS transistor, a first end of the third PMOS transistor is coupled to the first end of the second PMOS transistor, and a second end of the third PMOS transistor is coupled to the first a second end of the second PMOS transistor, a control end of the third PMOS transistor coupled to the input of the first comparator And a first resistor, a first end of the first resistor is coupled to the second end of the second PMOS transistor and the second end of the third PMOS transistor, the first resistor A second end is coupled to a ground, wherein the first voltage is generated at the first end of the first resistor. The lithium battery control circuit of claim 1, wherein the smoothing conversion circuit comprises: a fourth PMOS transistor; a second resistor, a first end of the second resistor coupled to the fourth a second end of the PMOS transistor, a second end of the second resistor is coupled to a ground; a fifth PMOS transistor, a first end of the fifth PMOS transistor is coupled to the fourth PMOS a first end of the crystal, a control end of the fifth PMOS transistor is coupled to a control end of the fourth PMOS transistor; a second current source, a first end of the second current source is coupled to the first end a second end of the fifth PMOS transistor, a second end of the second current source is coupled to the ground end; a switch, a control end of the switch receives the mode signal, a first end of the switch is coupled to the a first end of the second resistor; and a third resistor, a first end of the third resistor is coupled to a second end of the switch, and a second end of the third resistor is coupled to the second end a ground terminal; wherein the second voltage is generated at the first end of the second resistor. The lithium battery control circuit of claim 3, wherein when the mode signal indicates the first charging mode, the switch causes the second resistor to be in parallel with the third resistor when the mode signal indicates In the non-first charging mode, the switch disables the third resistor. The lithium battery control circuit of claim 1, wherein the smoothing conversion circuit comprises: a second comparator, a first input of the second comparator receives the first voltage, and the second comparator A second input receives the second voltage, and an output of the second comparator outputs the reset signal. The lithium battery charging control circuit of claim 1, wherein the off time control circuit comprises: a sixth PMOS transistor; a seventh PMOS transistor, a first end coupling of the seventh PMOS transistor Connected to a first end of the sixth PMOS transistor, a control terminal of the seventh PMOS transistor is coupled to a second end of the sixth PMOS transistor and a control terminal; a first NMOS transistor, the first a first end of the NMOS transistor is coupled to the second end of the sixth PMOS transistor and the control end; a fourth resistor, a first end of the fourth resistor is coupled to the first NMOS a second end of the crystal, a second end of the fourth resistor is coupled to a ground; a third comparator, a first input of the third comparator receives the feedback signal, the third comparison a second input end of the fourth resistor is coupled to the first end of the fourth resistor and the second end of the first NMOS transistor, and an output end of the third comparator is coupled to the first NMOS transistor a first capacitor, a first end of the first capacitor coupled to a first portion of the seventh PMOS transistor a second end of the first capacitor is coupled to the ground; a second NMOS transistor, a first end of the second NMOS transistor is coupled to the first end of the first capacitor, the second a second end of the NMOS transistor is coupled to the ground, a control end of the second NMOS transistor receives the duty ratio signal; and a fourth comparator, a first input of the fourth comparator is coupled The second end of the seventh PMOS transistor and the first end of the first capacitor, a second input of the fourth comparator receives a second reference voltage, and an output of the fourth comparator outputs This setting signal. The lithium battery control circuit of claim 6, wherein a current ratio of the sixth PMOS transistor and the seventh PMOS transistor is N:1, wherein a current through the seventh PMOS transistor is defined It is the first current, and N is a positive number. The lithium battery control circuit of claim 7, wherein the shutdown time control circuit charges the first capacitor using the first current according to the duty ratio signal to obtain a shutdown linearly related to the output voltage. time. The lithium battery control circuit of claim 1, further comprising: a logic control circuit coupled to the smoothing conversion circuit and the off time control circuit, and generated according to the reset signal and the setting signal The pulse frequency is modulated by the duty ratio signal. The lithium battery control circuit of claim 1, wherein the first charging mode is a low current mode. A lithium battery charger includes: a lithium battery control circuit, comprising: a smoothing conversion circuit, generating a first voltage according to a sensing current signal and a feedback signal, and generating a second voltage according to a mode signal, And comparing the first voltage with the second voltage to generate a reset signal, wherein the feedback signal is related to an output voltage, the mode signal is used to indicate whether it is in a first charging mode, and in the first charging mode The second voltage is less than the second voltage in the non-first charging mode; and a shutdown time control circuit converts the feedback signal by a voltage conversion current mechanism to generate a first current and uses The first current and a duty ratio signal are used to generate a set signal; a current sensing circuit for generating the sensing current signal according to an output current; and a feedback circuit for generating the output voltage according to an output voltage Feedback signal. The lithium battery charger of claim 11, further comprising a driving circuit, wherein the lithium battery control circuit further comprises a logic control circuit, the logic control circuit generating the working ratio according to the reset signal and the setting signal A signal is applied to the drive circuit and fed back to the off-time control circuit.