JP2004023948A - Multi-channel power supply circuit arrangement, power supply control integrated circuit, and soft start circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor integrated circuit and multichannel power supply circuit arrangement of small size and low cost, capable of setting a start timing for each output channel. <P>SOLUTION: The start timing of a switching power supply circuit of a plurality of channels, of the multichannel power supply circuit arrangement, is decided by each of control signals CNT1-CNT4. A soft start signal generating block 20 comprises 4-channel soft start circuits CH.1-CH.4 each of which is composed of a counter circuit 21, a latch circuit 22, a DA convertor 23, a comparison circuit 24, and an OR gate 25. An oscillator 10 which comprises soft start set terminals 30 as one collective terminal is shared by the 4-channel soft start signal generation block 20, and a basic pulse Pbp is generated at such oscillation cycle as corresponds to the resistance value of a resistor Rd connected to the soft start set terminal 30. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a soft start circuit for generating a soft start signal for preventing a rush current to a switching power supply circuit, a power supply control integrated circuit for controlling a start timing of the switching power supply circuit by a start signal, and switching of a plurality of channels. The present invention relates to a multi-channel power supply circuit device in which the start timing of a power supply circuit is determined by each start signal.
[0002]
[Prior art]
FIG. 4 is a circuit diagram showing an example of a PWM type switching power supply circuit, and shows a circuit configuration for one channel.
[0003]
In this switching power supply circuit, a series circuit of an inductor L and a switching transistor M is arranged between the DC input voltage Vin and the ground, and an anode of the diode D is connected to a connection point between the inductor L and the switching transistor M. The cathode of the diode D is connected to an output terminal to which a load (not shown) is connected, and is grounded via an output capacitor C, thereby constituting a DC / DC converter for supplying an output voltage Vout to the load.
[0004]
FIG. 5 is a block diagram showing a conventional soft start IC circuit.
The IC circuit for controlling the switching power supply circuit includes a charging block 1 for charging the capacitor C1 by the current source I, and a circuit block 2 for comparing the charging voltage Va of the capacitor C1 with the reference triangular wave Str. The circuit block 2 constitutes a soft-start circuit that gradually widens the on-duty of the switching transistor M immediately after startup. In this soft start circuit, the comparator 3 generates a gradually widening switching pulse to gradually increase (soft start) the output voltage.
[0005]
In the switching power supply circuit, the soft start circuit in FIG. 5 is a circuit that gradually widens the pulse signal width for switching in order to prevent an inrush current generated in the power supply circuit when the power supply is started. The soft start signal is generally generated by comparing the charging voltage to the capacitor C1 with the reference triangular wave Str by the comparator 3.
[0006]
Note that, in general, a circuit configuration in which charging is performed by a resistor instead of the current source I of the charging block 1 may be employed.
When there are a plurality of output channels, the charging block 1 and the circuit block 2 in FIG. 5 are required for the number of output channels in order to make the start timing of each output channel different. The external capacitor C1 used in that case generally has a size of several nF to several μF, and a capacitor of about several pF that can be built in an IC circuit cannot be enough. Therefore, a plurality of capacitors are used as external components in the IC circuit. Then, the timing of starting the power supply for each output channel is controlled by using the switch of the Nch MOSFET Q, and is determined by the charging start time of the capacitor C1.
[0007]
FIG. 6 is a timing chart showing operation signals of the soft start circuit shown in FIG.
6, a soft start signal SS1 output as a square wave from a comparator 3 is supplied as a control signal CT to a switching transistor M of a DC / DC converter in a switching power supply circuit. To the charging block 1, a feedback signal based on a difference between the output voltage of the DC / DC converter and its reference value is provided from an error amplifier or the like, and a control signal (duty signal) CT suitable for the DC / DC converter is correspondingly provided. Is output. By providing such a duty signal to the switching transistor M to perform on / off control, the output voltage Vout of the DC / DC converter can be regulated to a predetermined voltage value.
[0008]
With only a normal PWM type switching power supply circuit without a soft start circuit, since the output voltage is insufficient immediately after the power supply is started at time t0, a signal of the maximum duty is supplied to the switching power supply circuit. However, since the output capacitor C is not charged immediately after the power is turned on, the output current is apparently substantially equivalent to the short-circuit state, and the current flowing through the inductor L is infinitely large. Therefore, a large current flows through the inductor L until the output voltage reaches a specified value, which may lead to destruction of the inductor L and the switching transistor M. Therefore, by gradually increasing the ON width by the soft start circuit, and gradually increasing the current flowing through the inductor L, the output capacitor C is also gradually charged, and can reach a specified output voltage. The time (from time t0 to t1) until the capacitor charging voltage Va reaches the voltage lower limit VL of the reference triangular wave Str is the delay period of the soft start signal.
[0009]
Now, in a switching power supply circuit having a plurality of output channels, when the startup timings of the output channels are different and a soft start circuit cannot be shared, a soft start circuit corresponding to each output channel is required. Therefore, in order to provide the capacitor C1 outside the charging block 1 and the circuit block 2 of the IC circuit, the soft start setting terminals 4 for connecting the capacitors C1 by the number of output channels are required.
[0010]
[Problems to be solved by the invention]
As described above, in a large-scale power supply circuit device, the number of output channels increases, and not only the number of soft start setting terminals of the IC circuit shown in FIG. 5 increases, but also the number of components such as capacitors increases. Therefore, in the conventional multi-channel power supply circuit device, there is a limit in reducing the size and cost of the power supply IC circuit and the power supply circuit device itself.
[0011]
Further, in the case where the soft start circuit generates a soft start signal by passing the capacitor charging voltage Va and the reference triangular wave Str through the comparator 3, the soft start circuit performs a soft operation until the capacitor charging voltage Va reaches the voltage lower limit value VL of the reference triangular wave Str. No start signal is generated. Therefore, there is also a problem that a predetermined delay period occurs after the start of the specific power supply channel, and the delay period becomes almost the same or longer than the actual soft start signal generation period.
[0012]
SUMMARY OF THE INVENTION An object of the present invention is to provide a small-sized and low-cost power supply control integrated circuit and a multi-channel power supply circuit by integrating a soft start setting terminal into one terminal while ensuring that start timing can be set for each output channel. It is to provide a device.
[0013]
Another object of the present invention is to provide a soft start circuit capable of reducing a delay time from the start of power supply to the generation of a soft start signal.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, there is provided a multi-channel power supply circuit device provided with a switching power supply circuit of a plurality of channels whose power-on timing is determined by a start signal for each channel. This multi-channel power supply circuit device is provided for each channel of the switching power supply circuit, and generates a soft start signal so as to prevent an inrush current to the switching power supply circuit. And an oscillator that generates a basic pulse that defines a period for generating the soft start signal in accordance with the size of the oscillation cycle.
[0015]
According to such a multi-channel power supply circuit device, the start timing of the switching power supply circuit can be set for each channel, and the soft start setting terminal can be integrated into one terminal. It is possible to reduce the size and cost.
[0016]
Further, according to the present invention, there is provided a power supply control integrated circuit for determining a start timing of a switching power supply circuit by a start signal. The power supply control integrated circuit includes a soft start setting terminal, an oscillator that generates a basic pulse at an oscillation cycle corresponding to a resistance value of a resistor connected to the soft start setting terminal, and a basic pulse output from the oscillator. A counter circuit that counts the number of pulses to generate a digital signal of a plurality of bits, a DA converter that outputs a sequentially increasing analog signal based on the digital signal counted up by the counter circuit, and an analog signal of the DA converter Is supplied as a comparison signal for the reference triangular wave, and a comparison circuit that generates a soft start signal whose output voltage gradually increases.
[0017]
According to such a power supply control integrated circuit, when the counting operation in the counter circuit is started by the start signal, the power supply control integrated circuit can be reduced in size and cost.
[0018]
Further, according to the present invention, there is provided a soft start circuit for generating a soft start signal when a power supply of a switching power supply circuit is started. The soft start circuit includes a soft start setting terminal that defines a power-on timing of the switching power supply circuit, and an oscillator that generates a basic pulse with an oscillation cycle according to a resistance value of a resistor connected to the soft start setting terminal. A counter circuit that counts the number of basic pulses output from the oscillator to generate a digital signal of a plurality of bits, and outputs an analog signal that sequentially increases based on the digital signal counted up by the counter circuit. And a soft start signal for gradually increasing the output voltage regardless of the magnitude of the output voltage commanded to the switching power supply circuit. And a comparing circuit to be used.
[0019]
According to such a soft start circuit, it is possible to reduce the delay time from when the power is turned on to when the soft start signal is generated.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing a configuration of a power supply control integrated circuit of the present invention.
[0021]
In the figure, reference numeral 10 denotes an oscillator for generating a basic pulse Pbp. The oscillator 10 is provided as an oscillator dedicated to the soft start function commonly used for the soft start signal generation block 20 of four channels.
[0022]
The oscillator 10 generates a basic pulse Pbp at an oscillation cycle corresponding to the resistance value of the resistor Rd connected to the soft start setting terminal 30. The basic pulse Pbp is a rectangular pulse having an oscillation period Tbp, as described later.
[0023]
The soft start signal generation block 20 includes a four-channel soft start circuit CH. 4 including a counter circuit 21, a latch circuit 22, a DA converter 23, a comparison circuit 24, and an OR gate 25. 1 to CH. 4 is included. These soft start circuits CH. 1 to CH. 4 is commonly supplied with a basic pulse Pbp generated by the oscillator 10. In FIG. 1, the soft start circuit CH. 1 is shown, and the remaining soft start circuit CH. 2-CH. 4 omits the components other than the counter circuit 21.
[0024]
The soft start circuit CH. 1 is connected to a PWM type switching power supply circuit as shown in FIG. 4, and generates a soft start signal SS1 for preventing an inrush current. Similarly, the soft start circuit CH. 2-CH. In step 4, soft start signals SS2 to SS4 for preventing inrush current to the switching power supply circuit connected to each of them are generated.
[0025]
In this case, the timing for starting the four-channel switching power supply circuit is determined by the respective control signals CNT1 to CNT4 (starting signal), and the oscillator 10 commonly connected to the soft start signal generation block 20 uses the basic pulse The generation period of the soft start signals SS1 to SS4 is defined by the oscillation cycle of Pbp. That is, the power supply control integrated circuit includes the soft start circuits CH. 1 to CH. 4 constitutes a multi-channel power supply circuit device that can determine the activation timing of the switching power supply circuit of a plurality of channels (here, channels CH.1 to CH.4) by the respective control signals CNT1 to CNT4. .
[0026]
Next, the soft start circuit CH. The configuration of a single channel of the power supply control integrated circuit will be described by taking 1 as an example.
The counter circuit 21 receives the basic pulse Pbp from the oscillator 10 and counts up the number of pulses to count up the 4-bit digital signals S1 to S4. The control signal CNT1 is supplied as a reset signal of the counter circuit 21, and the control signal CNT1 is input to the soft start circuit CH. When 1 is activated, the reset of the counter circuit 21 is released, and the counting operation of the basic pulse Pbp is started. Although the counter circuit 21 shown in FIG. 1 has a 4-bit output (S1 to S4), an arbitrary multi-bit output counter circuit can be used.
[0027]
The latch circuit 22 is supplied with the control signal CNT1 and the most significant bit signal S4 of the digital signals S1 to S4 of the counter circuit 21 as a reset signal and a data latch clock, respectively. The control signal CNT is input and the soft start circuit CH. When the activation of 1 starts, the reset of the latch circuit 22 is released. In addition, the input “H” (logical value 1) is latched in synchronization with the falling edge (timing of changing from 1 to 0) of the most significant bit signal S4, and the soft start completion signal SF1 is set to “H”. .
[0028]
In FIG. 1, the most significant bit is the fourth digital signal S4. However, when a 5-bit output counter circuit is used, it is necessary to output a soft start completion signal synchronized with the digital signal S5.
[0029]
The DA converter 23 receives the digital signals S1 to S4 from the counter circuit 21, converts the digital signals S1 to S4 into an analog signal Vs which has been resistance-divided in 16 stages, and outputs the analog signal Vs. In order to divide the analog signal Vs by 16 steps, a series resistor circuit of 16 resistors R1 to R16 is used. The analog signal Vs output from the DA converter 23 is sequentially switched one step at a time in accordance with the 4-bit digital signals S1 to S4, and is converted into a voltage value of 16 (= 2 ⁴ ) steps divided by the resistance from the series resistor circuit. Correspondingly, it is output as a voltage signal that rises sequentially. In the DA converter 23, the magnitude of the analog signal Vs corresponding to the minimum value of the digital signals S1 to S4 is determined by the soft start circuit CH. 1 to CH. 4 is set to be equal to the voltage lower limit value VL of the reference triangular wave Stri supplied commonly.
[0030]
The comparison circuit 24 is supplied with the analog signal Vs of the DA converter 23 as a comparison signal for the reference triangular wave Stri, and outputs the comparison output Sout as a soft start signal SS1 via the OR gate 25. It becomes the command voltage.
[0031]
The OR gate 25 receives the soft start completion signal SF1 synchronized with the falling edge of the most significant bit S4 of the counter circuit 21 and the comparison output Sout of the comparison circuit 24, and performs a logical sum operation. In the OR gate 25, once the activation of the switching power supply circuit is completed by the soft start signal SS1, the comparison output Sout of the comparison circuit 24 is inhibited as the soft start signal SS1, and the soft start circuit CH. 1 outputs a soft start completion signal SF1.
[0032]
2 and 3 are timing charts showing the operation of the power supply control integrated circuit of FIG. FIGS. 2A and 3A show the control signal CNT1 that switches to the H level at time t0.
[0033]
FIG. 2B shows a basic pulse Sbp, which is an input / output signal of the counter circuit 21, and digital signals S1 to S4. FIG. 3C shows an analog signal Vs, which is an input / output signal of the comparison circuit 24, and a reference triangular wave Stri.
[0034]
FIG. 3B shows a digital signal S4 which is an input signal of the latch circuit 22. FIG. 7C shows a state in which the same analog signal Vs and the reference triangular wave Str are input after the end of the soft start. FIG. 2D shows the soft start completion signal SF1, and FIG. 2E shows the soft start signal SS1.
[0035]
The basic pulse Sbp shown in FIG. 2B is a soft start circuit CH. 1 to CH. 4 are input to the respective counter circuits 21. Since the control signal CNT1 is a reset signal of the counter circuit 21, the reset state of the counter circuit 21 is released when the activation is started. Therefore, the counting operation starts, and the digital signals S1 to S4 are output to the DA converter 23. The counter circuit 21 continues the power counting in binary with the input of the basic pulse Sbp. When the 4-bit output is input to the DA converter 23, as shown in FIG. 2C, the voltage of the analog signal Vs obtained by sequentially switching the voltage of the resistance division step by step according to the 4-bit binary number is changed. Are output from the DA converter 23 to the comparison circuit 24 while gradually rising. Here, since the initial state voltage of the analog signal Vs is set to be equal to the voltage lower limit value VL of the reference triangular wave Str, the delay time from the start of the control signal CNT1 to the generation of the soft start signal SS1 is the same as the conventional delay time shown in FIG. It is greatly reduced compared to the one shown in the above.
[0036]
FIG. 3E shows a soft start signal SS1 output when the analog signal Vs is input to the comparison circuit 24 and compared with the reference triangular wave Str. The switching width of the soft start signal SS1 gradually increases with time, and is fixed to the high level H after time t2.
[0037]
Note that, even if the counter circuit 21 finishes counting up to the most significant bit, the basic pulse Sbp continues to be supplied, so that the counter circuit 21 returns the count value to the beginning and repeats counting. Here, the comparison circuit 24 repeatedly compares the analog signal Vs of the DA converter 23 with the reference triangular wave Stri. Therefore, the falling edge of the most significant bit signal S4 of the counter circuit 21 is latched by the latch circuit 22 to generate a soft start activation completion signal SF1 as shown in FIG. Is completed, the soft start signal SS1 is fixed to the H side.
[0038]
In the above-described power supply control integrated circuit, the case where soft start is required for four channels has been described. However, as external components, only the resistor Rd connected to the soft start setting terminal 30 is used regardless of the number of channels, and the soft start signal generation block It is possible to arrange as many soft start circuits as necessary in the number of channels 20.
[0039]
Further, the number of bits can be arbitrarily selected in the counter circuit 21. In general, when the number of bits is n, the resistance voltage which can be set is 2 ⁿ steps.
Further, the time from the time t0 when the control signal is applied to the soft start circuit to the completion t2 of the soft start activation can be calculated as Tbp × ²ⁿ . In the DA converter 23, the transition time per stage is Tbp, and the on-duty of the switching pulse per stage is calculated as VDA / (2 ⁿ × ΔVosc). Here, ΔVDA is the difference voltage between the maximum value and the minimum value of the resistance voltage dividing point of the DA converter 23, and ΔVosc is the amplitude voltage of the reference triangular wave Stri.
[0040]
【The invention's effect】
As described above, according to the multi-channel power supply circuit device of the present invention, the start timing can be set for each output channel, and the soft start setting terminals can be integrated into one terminal. As a result, there is an advantage that as the number of output channels increases, the effects of reducing the size and cost of the power supply circuit appear.
[0041]
Further, according to the soft start circuit of the present invention, the delay time from when the power is turned on to when the soft start signal is generated can be reduced to substantially zero. , The timing can be easily set, and the start-up time can be reduced.
[0042]
Further, according to the power supply control integrated circuit of the present invention, the conventional capacitor is stopped and a resistor is used as an electronic component for setting the start time of the soft start. There is an advantage that can be reduced. Furthermore, since the time constant can be set in finer increments than the capacitor by using the resistor, there is an advantage that the adjustment of the constant becomes easy and the degree of freedom in design is increased.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a power supply control integrated circuit of the present invention.
FIG. 2 is a timing chart showing an operation of the power supply control integrated circuit of FIG. 1;
FIG. 3 is a timing chart showing an operation of the power supply control integrated circuit of FIG. 1;
FIG. 4 is a circuit diagram illustrating an example of a PWM switching power supply circuit.
FIG. 5 is a block diagram showing a conventional soft start IC circuit.
FIG. 6 is a timing chart showing operation signals of the IC circuit for soft start of FIG. 5;
[Explanation of symbols]
10 Oscillator 20 Soft start signal generation block CH. 1 to CH. 4 Soft start circuit 21 Counter circuit 22 Latch circuit 23 DA converter 24 Comparison circuit 25 OR gate 30 Soft start setting terminal Rd Resistance CNT1 to CNT4 Control signal S1 to S4 Digital signal Sout Comparison output SS1 to SS4 Soft start signal Pbp Basic pulse Vs Analog signal Stri reference triangle wave

Claims (7)

In a multi-channel power supply circuit device in which the start timings of the switching power supply circuits of a plurality of channels are determined by respective start signals,
A soft start circuit that is provided for each channel of the switching power supply circuit and generates a soft start signal for preventing an inrush current to the switching power supply circuit;
An oscillator that is provided in common to all of the soft start circuits and generates a basic pulse that defines a generation period of the soft start signal according to the size of the oscillation cycle;
A multi-channel power supply circuit device comprising: The soft start circuit,
A counter circuit that counts basic pulses output from the oscillator and counts up a digital signal of a plurality of bits,
A DA converter that outputs a sequentially increasing analog signal based on the digital signal counted up by the counter circuit;
A comparison circuit that supplies an analog signal of the DA converter as a comparison signal with respect to a reference triangular wave and generates a soft start signal by a gradually increasing comparison output;
The multi-channel power supply circuit device according to claim 1, further comprising: In a power supply control integrated circuit configured to control a start-up timing of a switching power supply circuit by a start signal,
A soft start setting terminal for connecting a resistor,
An oscillator that generates a basic pulse at a predetermined oscillation cycle according to a resistance value of a resistor connected to the soft start setting terminal;
A counter circuit that counts basic pulses output from the oscillator and generates a digital signal of a plurality of bits,
A DA converter that outputs a sequentially increasing analog signal based on the digital signal counted up by the counter circuit;
A comparison circuit that supplies an analog signal of the DA converter as a comparison signal with respect to a reference triangular wave and generates a soft start signal by a gradually increasing comparison output;
Wherein the counting operation of the counter circuit is started by the start signal. A power supply control integrated circuit for controlling a switching power supply circuit of a plurality of channels,
For a common basic pulse generated by the oscillator, the counter circuit, the DA converter, and a plurality of soft start signal generation block composed of the comparison circuit,
4. The power supply control integrated circuit according to claim 3, wherein the activation timings of the switching power supply circuits of a plurality of channels are respectively determined by a soft start signal output from the soft start signal generation block. A latch circuit for latching data 1 at a timing when the most significant bit of the digital signal of the counter circuit changes from 1 to 0 by the start signal;
A gate circuit that outputs the soft start signal by performing a logical sum operation between an output of the latch circuit and a comparison output of the comparison circuit;
The power supply control integrated circuit according to claim 3, further comprising: In a soft start circuit that generates a soft start signal to prevent inrush current to the switching power supply circuit,
A soft start setting terminal to which a resistor that defines a start timing of the switching power supply circuit is connected;
An oscillator that generates a basic pulse with an oscillation cycle according to a resistance value of a resistor connected to the soft start setting terminal;
A counter circuit that counts basic pulses output from the oscillator and generates a digital signal of a plurality of bits,
A DA converter that outputs a sequentially increasing analog signal based on the digital signal counted up by the counter circuit;
A comparison circuit that supplies the analog signal of the DA converter as a comparison signal with respect to a reference triangular wave, and generates a soft start signal by a comparison output that gradually increases regardless of the magnitude of a command voltage to the switching power supply circuit;
A soft start circuit comprising: In the DA converter, the magnitude of the analog signal corresponding to the minimum value of the digital signal is set equal to the lower limit value of the voltage of the reference triangular wave, and the soft start signal is generated immediately after the counter circuit starts counting. 7. The soft start circuit according to claim 6, wherein:

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