CN100435460C - mode conversion control circuit and method for charge pump - Google Patents

Abstract

A mode conversion control circuit and method for a charge pump, the charge pump being operable in a plurality of multiplying power modes, the method comprising: monitoring the charge pump to generate a mode up signal and a mode down signal; generating a modified pattern down signal from the pattern down signal at intervals; generating a mode selection signal according to the mode rising signal and the mode falling signal, and determining that the charge pump operates in one of the multiple multiplying power modes; and determining whether to output the mode selection signal according to the mode rising signal and the modified mode falling signal. When the input voltage is close to the mode switching point, the charge pump is switched to a lower multiplying power mode at intervals, so that the wrong judgment caused by noise, load change or inaccurate equivalent resistance of the charge pump is improved.

Description

Mode conversion control circuit and method of charge pump

technical field

The invention relates to a charge pump, in particular to a mode conversion control circuit and method of the charge pump.

Background technique

Today's electronic circuits often require more than one DC voltage power supply, so there are many systems used to convert power, and charge pumps are one of them. A charge pump is a circuit consisting of a capacitor and an oscillator that can step up or step down a DC input voltage for output. FIG. 1 is a performance curve diagram of a step-up charge pump in a 1X mode and a 1.5X mode, wherein curve 10 is the performance curve of the 1.5X mode, and curve 12 is the performance curve of the 1X mode. The charge pump generally uses the battery to provide the input voltage. As the usage time increases, the voltage of the battery becomes lower and lower. When the battery cannot supply enough voltage for the load, the charge pump will switch to a higher rate mode, such as 1 times mode. Switch to 1.5 times mode, as shown in dotted line 14; conversely, when the voltage gradually rises or the load decreases, etc., the charge pump will switch to a lower rate mode, for example, from 1.5 times mode to 1 times mode, as shown in the dotted line 16. In the known technology, it is necessary to calculate the equivalent resistance of the charge pump in order to judge when the multiplier mode should be switched. However, errors are often caused by factors such as accuracy, temperature effects, and noise interference in the calculation, which affects the judgment of the mode conversion. Therefore, a magnetic The hysteresis voltage delays the switching timing of the charge pump mode to avoid temporary wrong judgment. However, if the hysteresis voltage is too large, the timing of mode switching will be delayed for too long, resulting in loss of chip work efficiency, and if it is too small, it may lead to wrong judgment. Generally speaking, if the equivalent resistance of the charge pump can be calculated more accurately, a smaller hysteresis voltage can be used; otherwise, a larger hysteresis voltage must be used to prevent misjudgment of the mode conversion, just want to get Accurate equivalent resistance is bound to use more complex circuits to calculate.

Therefore, a mode conversion control circuit and method for a charge pump that does not need to accurately calculate the equivalent resistance of the charge pump and does not need to use a large hysteresis voltage to prevent misjudgment is desired.

Contents of the invention

One of the objectives of the present invention is to provide a mode conversion control circuit and method of a charge pump that does not need to use a large hysteresis voltage to prevent misjudgment.

One of the objectives of the present invention is to provide a mode conversion control circuit and method for a charge pump, which can eliminate errors in detection voltage caused by external noise or load changes.

One of the objectives of the present invention is to provide a mode conversion control circuit and method for a charge pump without accurately calculating the equivalent resistance of the charge pump.

According to the present invention, a mode switching control circuit and method of a charge pump includes using a mode monitor to monitor the charge pump to generate a mode up signal and a mode down signal, a mode decision logic based on the mode up signal and mode down signal Generate a mode selection signal for determining the charge pump to operate in one of multiple rate modes, a gating circuit generates a modified mode down signal from the mode down signal at intervals of a reference time, and a mode switching timing The device generates a mode conversion signal to the mode decision logic according to the mode up signal and the modified mode down signal to determine whether to output the mode selection signal.

Description of drawings

Figure 1 shows the performance curves of the charge pump in different rate modes;

Fig. 2 is an embodiment of the present invention;

FIG. 3 is a bidirectional mode conversion state diagram of the charge pump 30 in FIG. 2;

Fig. 4 is the embodiment of mode conversion timer 36 among Fig. 2;

Figure 5 is an embodiment of mode decision logic 38;

Figure 6 is an embodiment of the mode up monitor 342 in Figure 2; and

FIG. 7 is an embodiment of mode drop monitor 344 in FIG. 2 .

Symbol Description:

10 Efficacy curve of 1.5 times mode

12 Potency curve of 1x mode

14 mode rising curve

16 mode drop curve

18 LED driver

20 current source

22 LEDs

24 transistors

26 transistors

28 operational amplifier

30 charge pump

32 Mode conversion control circuit

34 mode monitor

342 Mode Rising Monitor

3422 comparator

344 mode drop monitor

3442 Current Source

3444 Current Source

3446 Comparator

36 Mode transition timer

3602 OR gate

3604 AND gate

3606 Inverter

3608 NAND gate

3610 charge and discharge circuit

3612 Current Source

3614 Inverter

3616 charge and discharge circuit

3618 Current Source

3620 Inverter

3622 Inverter

3624 Inverter

38 Mode decision logic

3802 logic circuit

3804 flip-flop

40 AND gate

42 reset timer

50 1x mode

52 1.5 times mode

54 2x mode

Detailed ways

FIG. 2 is an embodiment of the present invention. In the light-emitting diode driving device 18, the charge pump 30 converts the input voltage Vin into an output voltage Vout to drive the light-emitting diode 22. The current source 20 is connected between the input voltage Vin and the transistor 24 to emit light. The positive terminal of the diode 22 is connected to the input voltage Vin, and the negative terminal is connected to the output terminal Vout through the transistor 26. The operational amplifier 28 is used to compare the voltages V _A and V _B on the nodes A and B. When the voltages V _A and V _B are not equal, The operational amplifier 28 outputs the signal _Vfb to the gates of the transistors 24 and 26 to adjust the currents I1 and Iout passing through the transistors 24 and 26, thereby balancing the voltages V _A and V _B on the nodes A and B, and the mode switching control circuit 32 Then, the rate mode of the charge pump 30 is determined by monitoring the voltage V _B on the node B and the signal V _fb output by the operational amplifier 28 . FIG. 3 is a bidirectional mode switching state diagram of the charge pump 30 in FIG. 2 . Referring to FIG. 2 and FIG. 3 , when the driving device 18 is activated, the mode switching control circuit 32 sets the multiplication mode of the charge pump 30 to the preset 1x mode 50 , and then switches the multiplication mode of the charge pump 30 as required. When the charge pump 30 operates in the 1X mode 50 , if the mode switch control circuit 32 reaches the mode up condition, the charge pump 30 switches to the 1.5X mode 52 , otherwise it remains in the 1X mode 50 . When the charge pump 30 operates in the 1.5 times mode 52, if the mode conversion control circuit 32 reaches the mode up condition, then the rate mode of the charge pump 30 is converted to the 2 times mode 54, and if the mode down condition is reached, the charge pump 30 is switched to The magnification mode drops back to the 1x mode 50 , and when the mode up condition and the mode down condition are not met, the original 1.5x mode 52 is maintained. When the charge pump 30 operates in the 2x mode 54 , if the mode switching control circuit 32 reaches the mode-down condition, the charge pump 30 is switched to the 1.5x mode 52 , otherwise it remains in the 2x mode 54 .

Referring to Fig. 2, in the mode switching control circuit 32, the mode monitor 34 monitors the voltage V _B on the node B and the signal V _fb output by the operational amplifier 28, and when the mode rising condition is reached, the mode rising monitor in the mode monitor 34 The device 342 generates the mode up signal U to the mode decision logic 38, and when the mode down condition is reached, the mode down monitor 344 in the mode monitor 34 generates the mode down signal D to the mode decision logic 38, and resets the timer 42 every A reference time, such as 100ms, outputs a pulse signal RS, and the mode down signal DB outputted by the AND gate 40 according to the mode down signal D and the pulse signal RS supplied by the reset timer 42, and the mode switching timer 36 according to the signal U and DB generate the mode conversion signal tt, and the mode decision logic 38 generates the mode selection signal x1, x1.5 or x2 according to the mode rising signal U and the mode falling signal D, which can be used to determine the operation of the charge pump 30 at 1 times, 1.5 times or 2 times magnification mode, and decide whether to output the mode selection signal x1, x1.5 or x2 according to the mode conversion signal t t.

FIG. 4 is an embodiment of the mode conversion timer 36 in FIG. 2, wherein the OR gate 3602 outputs the signal S1 according to the signals DB and U, and the AND gate 3604 outputs the signal S2 according to the signal S1 and the enable signal EN, and the soft activation signal soft_start is inverted. The device 3606 generates the signal S3, and the NAND gate 3608 outputs the control signal S4 according to the signals S2, S3 and V _C2 ' to control the charging and discharging of the charging and discharging circuit 3610 to generate a mode conversion signal tt, and the charging and discharging circuit 3616 is controlled by the signal tt to generate a timing signal V _C2 '. In the charging and discharging circuit 3610, the current source 3612 and the switch SW1 are connected in series between the input voltage Vin and the ground GND, the capacitor C1 is connected in parallel with the switch SW1, and the control signal S4 switches the switch SW1 so that the current source 3612 charges and discharges the capacitor C1 to generate a signal V _C1 , the signal V _C1 forms the mode conversion signal tt through the inverter 3614 . In the charging and discharging circuit 3616, the current source 3618 and the switch SW2 are connected in series between the input voltage Vin and the ground GND, the capacitor C2 is connected in parallel with the switch SW2, and the signal tt switches the switch SW2 so that the current source 3618 charges and discharges the capacitor C2 to generate a signal V _C2 , The inverters 3620, 3622 and 3624 form a delay circuit to delay the signal V _C2 to obtain the signal V _C2 ′.

Fig. 5 is an embodiment of the mode decision logic 38, in which the logic circuit 3802 generates a signal S5 to the flip-flop 3804 according to the mode up signal U and the mode down signal D, and the flip-flop 3804 when the signal tt changes from a low level to a high level 3804 is triggered, if the signal S5 is at a high level at this time, a signal is generated by the output terminal Q so that the mode decision logic 38 outputs the mode selection signal x1.5 to the charge pump 30, and if the signal S5 is at a low level, the output The terminal Q generates a signal to make the mode decision logic 38 output the mode selection signal x1 to the charge pump 30. After the flip-flop 3804 is triggered, the output terminal Q will maintain the trigger level until the flip-flop 3804 is triggered again . This embodiment is to illustrate the function of the mode switching signal tt in the mode decision logic 38 , therefore, not all circuits in the mode decision logic 38 are shown.

FIG. 6 is an embodiment of the mode-up monitor 342 in FIG. 2, which includes a comparator 3422 to monitor the signal V _fb , and when the mode-up condition is met, that is, V _fb >(Vin-V _TP ), where V _TP is a preset When the voltage is set, the comparator 3422 outputs a mode up signal U. FIG. 7 is an embodiment of the mode drop monitor 344 in FIG. 2, which includes a current source 3442 supplying a current I2 through a resistor R1 to generate a voltage V1, wherein the current I2 and the current Iout through the transistor 26 are shown in FIG. proportional relationship, that is

I2＝Iout×(1/k) Formula 1

Among them, k is a constant. while the resistance

R1＝k×(R _eq +R _drop ) Formula 2

Wherein, _Req is the equivalent resistance of the charge pump 30 , R _drop is the conduction resistance of the transistor 26 , and the charge pump 30 has different equivalent resistances _Req in different rate modes. The voltage can be obtained from formulas 1 and 2

V1＝Iout×(R _eq +R _drop ) Formula 3

In addition, the current source 3444 supplies the current I _hyst to generate the hysteresis voltage V _hyst through the resistor R2. In this embodiment, the current I _hyst is much smaller than the current I2 so it is ignored in the formula 3. The comparator 3446 monitors the voltage V B on the node _B , when the mode-down condition is met, that is, V _B >(V1+V _hyst ), the comparator 3446 outputs the mode-down signal D.

Referring to FIG. 2 to FIG. 7 , assuming that the input voltage Vin rises close to the mode switching point, for example, 3.5V, without accurately calculating the equivalent resistance value _Req of the charge pump 30 and using a smaller hysteresis voltage V _hyst , The mode monitor 34 may reduce the rate mode of the charge pump 30 in advance, for example, switch from the 1.5 times mode to the 1 times mode, after switching the charge pump 30 to the 1 times mode, if the output voltage Vout of the charge pump 30 at this time is sufficient to drive Diode 22 maintains the current multiplier mode, otherwise, it immediately outputs the mode up signal U to switch the charge pump 30 back to the 1.5 times mode. After switching back to the 1.5 times mode, although the mode monitor 34 immediately outputs the mode down signal D to mode decision logic 38, but it has to wait for a period of time until the corrected mode down signal DB appears, then switch the charge pump 30 from 1.5 times mode to 1 times mode again and repeat the above steps. In other words, when the input voltage Vin is close to the mode switching point, the mode conversion control circuit 32 switches the charge pump 30 to the previous rate mode at regular intervals, such as switching from the 2 times mode to the 1.5 times mode or from the 1.5 times mode to 1 multiplier mode, and detect whether the output voltage Vout is sufficient to drive the diode 22, and if not, immediately switch back to the previous multiplier _mode . In the case of the voltage V _hyst , even without using the hysteresis voltage V _hyst , it is still possible to prevent erroneous judgments and eliminate errors in the detection voltage caused by external noise or load changes, and because the charge pump 30 does not need to be accurately calculated The equivalent resistance R _eq , therefore no complex calculation circuit is needed, so the complexity of the mode conversion control circuit 32 can be reduced.

Claims (5)

1. A mode conversion control method of a charge pump, the charge pump operates in a plurality of multiplier modes, the method comprising: monitoring the charge pump to generate a mode up signal and a mode down signal; generating a modified mode-down signal from the mode-down signal at intervals; and generating a mode selection signal according to the mode-up signal and the mode-down signal for determining that the charge pump operates in one of the plurality of multiplier modes; Whether to output the mode selection signal is determined according to the mode up signal and the modified mode down signal. 2. The mode conversion control method of the charge pump as claimed in claim 1, wherein the step of determining whether to output the mode selection signal according to the mode up signal and the modified mode down signal comprises: generating a control signal based on the mode up signal, the modified mode down signal and a timing signal; Using the control signal to charge and discharge a first capacitor to generate a mode switching signal to determine whether to output the mode selection signal; and The timing signal is generated by charging and discharging a second capacitor according to the mode switching signal. 3. A mode switching control device of a charge pump, the charge pump operates in multiple multiplier modes, the device comprising: a mode-up monitor for monitoring the charge pump to generate a mode-up signal; a mode-down monitor for monitoring the charge pump to generate a mode-down signal; a gating circuit for generating a modified mode-down signal from the mode-down signal at intervals of a reference time; a mode decision logic, which generates a mode selection signal according to the mode up signal and the mode down signal for determining that the charge pump operates in one of the multiple rate modes; and A mode conversion timer provides a mode conversion signal to the mode decision logic according to the mode up signal and the modified mode down signal to determine whether to output the mode selection signal. 4. The mode conversion control device of the charge pump as claimed in claim 3, wherein the gating circuit comprises: A reset timer generates a pulse signal having a period equal to the reference time; and An AND gate, outputting the modified mode-down signal according to the pulse wave signal and the mode-down signal. 5. The mode conversion control device of the charge pump as claimed in claim 3, wherein the mode conversion timer comprises: a logic circuit for generating a control signal based on the mode up signal, the modified mode down signal and a timing signal; A first charging and discharging circuit, generating the mode switching signal according to the control signal; and A second charging and discharging circuit is controlled by the mode switching signal to generate the timing signal.

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