Switching regulator having overcurrent protection function and electronic apparatus using the regulator

The present invention relates to a switching regulator technology that controls an output voltage and an output current by controlling the pulse width of a pulse signal that drives an output transistor, and in particular, an overcurrent that leads to a short circuit and an overcurrent that does not lead to a short circuit. A switching regulator with a built-in overcurrent protection circuit that distinguishes between current cases and provides optimum protection for each, and an overcurrent protection circuit that responds to temporary (instantaneous) overcurrents due to noise, etc., in units of oscillation cycles. The present invention relates to a switching regulator incorporating the above, and various portable electronic devices such as a mobile phone, a PHS, a PDA, and a laptop computer incorporating the switching regulator.

In recent years, various portable electronic devices such as mobile phones, PHS (Personal Handyphone System), PDAs (Personal Digital Assistants), and laptop computers have become widespread. In these portable electronic devices, various power supply voltages are required to drive the internal circuit, and these various power supply voltages are generated in the power supply circuit using the battery voltage.

These portable electronic devices are required to be smaller, lighter, and lower in cost. Therefore, a power supply circuit using an efficient switching regulator is used, which generates various stable power supply voltages and supplies a stable power supply to the internal circuit.

Examples of the conventional switching regulator protection circuit include (1) JP-A-9-182277 Switching Regulator and (2) JP-A-7-327355 Switching Regulator Protection Circuit.

FIG. 4 is a diagram for explaining the switching regulator described in Japanese Patent Application Laid-Open No. 9-182277. In the figure, 1 is a control unit, Tr1 is an output transistor, Tr3 is a switching element, and L is a coil.

In the circuit of FIG. 4, the control unit 1 switches and drives the output transistor Tr1 with the control signal OUT of a constant frequency, and adjusts the duty of the control signal OUT based on the output voltage Tout output from the output terminal Tout. The output voltage Vout is maintained at a constant voltage.

The control unit 1 includes a short-circuit protection circuit 2 that cuts off the output transistor Tr1 when the output voltage Vout falls below a predetermined voltage. Between the coil L and the output terminal Tout, when the output transistor Tr1 operates based on the control signal OUT, it turns on and operates as a diode, and based on the output signal of the short-circuit protection circuit 2, the coil L and the output terminal Tout A switching element Tr3 that cuts off the connection is provided.

FIG. 5 is a diagram for explaining the switching regulator described in Japanese Patent Application Laid-Open No. 7-327355. In the figure, 5 is a switching regulator composed of a drive transistor 6, a diode 7, a coil 8, and a capacitor 9, 10 is a drive circuit for driving the driver transistor 6, 11 is an output transistor 12 to 15, and a ground fault detection circuit. 17 and 18, BTL (Balanced Transistor) configuration output amplifier consisting of celestial junction detection circuits 19 and 20, 16 is a voltage detection circuit that detects that the power supply voltage has increased, 21 is an input amplifier, 22 is an output amplifier 11 A bias circuit for supplying a bias to the input amplifier 21, 23 shows a stop circuit for stopping the drive circuit 10 and the bias circuit 22.

In the circuit of FIG. 5, the stop circuit 23 is the output signal and power supply voltage Vcc of the ground fault detection circuits 17 and 18 or the ceiling fault detection circuits 19 and 20 indicating that the output transistors configured in the BTL are ground faults or sky faults. The output signal of the voltage detection circuit 16 indicating that the overvoltage / surge of is detected is input, and the stop signal is output to the drive circuit 10 and the bias circuit.

With this configuration, when a ground fault or a top fault of the output transistors constituting the output amplifier 11 is detected, the operation of the bias circuit is stopped to turn off the output transistors 12 to 15 and the driver transistors 6 are turned off. The transistor is protected from damage due to overvoltage / surge of the power supply voltage Vcc.

<patcit num="1"><text>Japanese Unexamined Patent Publication No. 9-182277</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 7-327355</text></patcit>

<p> As described above, in the switching regulator described in Japanese Patent Application Laid-Open No. 9-182277, the output transistor Tr1 is cut off and protected when the output voltage Tout becomes a predetermined voltage or less. However, even if the output voltage Tout drops below a predetermined voltage momentarily (temporarily) due to noise or the like, the protection circuit operates, and after that, the output transistor Tr1 is continuously turned off. There is a problem that it cannot be restored.</p><p> Further, in the circuit described in Japanese Patent Application Laid-Open No. 7-327355, when the output transistors 12 to 15 are short-circuited and an overcurrent flows, the driver transistor 6 of the switching regulator 5 is turned off and protected. However, this driver transistor 6 does not break when a current flows momentarily, even if it does not reach a ground fault, but it may break when a current flows for a long time.</p><p> An object of the present invention is to distinguish between an overcurrent that leads to a short circuit and an overcurrent that does not lead to a short circuit, and a switching regulator having an overcurrent protection function that provides optimum protection for each, momentary due to noise, etc. It is to provide a switching regulator having an overcurrent protection function corresponding to an overcurrent in units of oscillation cycles, and various portable electronic devices such as mobile phones, PHS, PDA and laptop computers incorporating the switching regulator. ..</p><p> More specifically, the invention according to (1) claims 1 to 3 has a switching having an overcurrent protection function that can protect the driver transistor by turning it off in the case of an overcurrent that does not lead to a short circuit. Providing a regulator, an overcurrent protection function that can periodically recover the driver transistor to deal with temporary (instantaneous, sudden) overcurrents such as noise that does not lead to a short circuit. It is an object of the present invention to provide a switching regulator having.</p><p>(2) The inventions according to claims 4 to 5 have a switching having an overcurrent protection function capable of continuously turning off and protecting the driver transistor (system down) in the case of an overcurrent leading to a short circuit. It is intended to provide a regulator.</p><p>(3) The inventions according to claims 6 to 7 aim to propose an application device using the switching regulator having the overcurrent protection function according to claims 1 to 5.</p>

<p> The present invention has the following means in order to achieve the above object. That is, a) The switching regulator having the overcurrent protection function according to the claim connects the first electrode (source) to the first power supply voltage (Vdd) and connects the second electrode (drain) to the oscillation output Lx. The driver transistor (Pch driver transistor 700) and the voltage at the high level of the oscillation output Lx, which operates only when the driver transistor (Pch driver transistor 700) is ON and fluctuates due to overcurrent, and the first reference voltage ( The output of the first comparator circuit (100) for comparing LMTREF1) and the output of the first comparator circuit (100) are smaller than the first reference voltage (LMTREF1) at the high level of the oscillation output Lx. When indicating that, the output from the PWM controller (500) is based on the output of the first latch circuit (200) holding the output of the first comparator circuit and the output of the first latch circuit (200). It is characterized by having an output control circuit (600) that controls whether or not a signal (800) is transmitted to a control electrode that controls on / off of the driver transistor (Pch driver transistor 700).</p><p> Further, the switching regulator having the overcurrent protection function according to claim 2 is characterized in that, in claim 1, the first latch circuit (200) is reset at a predetermined cycle.</p><p> Further, in the switching regulator having the overcurrent protection function according to claim 3, in claim 1 or 2, the first reference voltage indicates that the voltage at the high level of the oscillation output Lx is in the overcurrent state. It is characterized by having a voltage that becomes.</p><p> Further, the switching regulator having the overcurrent protection function according to claim 4 has a second reference voltage (LMTREF2) lower than the first reference voltage (LMTREF1) and an oscillation output in addition to the configurations of claims 1 to 3. The output of the second comparator circuit (300) comparing Lx and the output of the second comparator circuit (300) indicate that the high-level voltage of the oscillation output Lx is smaller than the second reference voltage (LMTREF2). In this case, the output of the second latch circuit (400) holding the output of the second comparator circuit (300) and the output of the second latch circuit (400) are input to the output control circuit (600), and the PWM controller is used. The feature is to control whether or not the output signal (800) from (500) is transmitted to the control electrode that controls the on / off of the driver transistor (Pch driver transistor 700).</p><p> Further, the switching regulator having the overcurrent protection function according to claim 5 is characterized in that the second reference voltage is a voltage that serves as a guide for indicating that the voltage at the high level of the oscillation output Lx is in a short-circuited state. It is supposed to be.</p><p> The electronic device according to claim 6 is an electronic device having a built-in switching regulator according to claims 1 to 5, and the portable electronic device according to claim 7 is a mobile phone, PHS, PDA, or laptop computer. It is characterized by being either.</p>

<p> According to the present invention, a switching regulator having an overcurrent protection function that distinguishes between an overcurrent that leads to a short circuit and an overcurrent that does not lead to a short circuit and provides optimum protection for each, momentary noise, etc. It is possible to realize a switching regulator having an overcurrent protection function corresponding to an overcurrent in units of oscillation cycles, and various electronic devices having a built-in switching regulator having the overcurrent protection function.</p><p> Specifically, (1) According to the inventions of claims 1 to 3, switching having an overcurrent protection function capable of turning off the driver transistor to protect an overcurrent that does not lead to a short circuit. Providing a regulator, an overcurrent protection function that can periodically recover the driver transistor to deal with temporary (instantaneous, sudden) overcurrents such as noise that does not lead to a short circuit. It is possible to realize a switching regulator having.</p><p>(2) According to the inventions of claims 4 to 5, an overcurrent protection function capable of continuously turning off the driver transistor to protect it (system down) in the case of an overcurrent leading to a short circuit is provided. It is possible to realize a switching regulator having.</p><p>(3) According to the inventions of claims 6 to 7, various electronic devices capable of protecting the driver transistor can be realized by using the switching regulator having the overcurrent protection function of claims 1 to 5.</p>

Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a switching regulator according to this embodiment. As shown in the figure, the switching regulator according to the present embodiment is based on a comparator 100 that compares the oscillation output Lx and the constant voltage LMTREF1, an SR latch circuit 200 that holds the output of the comparator 100, and the constant voltage LMTREF1. Comparator 300 comparing low voltage LMTREF2 with oscillation output Lx, SR latch circuit 400 holding the output of the comparator 300, PWM controller 500, passing the output 800 of PWM controller 500 through SR latch circuit 200 or SR latch circuit 400 It is composed of an output control circuit 600 for suppression control by a set output and a Pch driver transistor 700 whose on / off is controlled by the output of the output control circuit.

The output control circuit 600 has, for example, a circuit configuration that takes the logical sum of the set output of the SR latch circuit 200 and the set output of the SR latch circuit 400, and takes the logical product of the logical sum and the output 800 of the PWM controller 500 to output. Has. Further, the comparators 100 and 300 are configured to operate only when the Pch driver transistor 700 is on. Coil L and capacitance C indicate connecting components for connecting an external circuit (not shown) to the switching regulator.

2 and 3 are time charts of oscillation output Lx, overcurrent, output 800 from PWM controller 500, output 900 from PWM controller 500, to illustrate the operation of the switching regulator of FIG. 1. FIG. Shows the limit operation 1 and FIG. 3 shows a time chart for explaining the limit operation 2.

Hereinafter, the operation of the switching regulator according to this embodiment will be described with reference to FIGS.

(Explanation of limit operation 1) During normal operation, the SR latch 200 is reset, and the output control circuit 600 passes the output 800 (pulse width-modulated pulse train) from the PWM controller 500 to the Pch driver transistor 700. In addition to the gate of, the switching regulator is operating in the normal state. The period of operation in this normal state is shown by (a) in Fig. 2.

However, when an overcurrent flows through the output voltage Vout (whether instantaneous or continuous), the H level during the ON period of the oscillation output Lx becomes lower than the power supply voltage. When the H level of the oscillation output Lx on period and the constant voltage LMTREF1 are compared by the comparator 100 and the H level of the oscillation output Lx on period becomes lower than the constant voltage LMTREF1 (timing (a) in Fig. 2). ), The SR latch 200 is set by the output of the comparator 100.

The output control circuit 600 turns off the Pch driver transistor 700 without passing the output 800 from the PWM controller 500 by the set output of the SR latch 200, and forcibly sets the oscillation output Lx to 0 level. The period during which this SR latch 200 is set is indicated by (b) (section of limit operation 1). With this configuration, when an overcurrent flows through the output voltage Vout, the Pch driver transistor 700 can be protected without being destroyed.

After that, the SR latch 200 is reset by the signal 900 created by the PWM controller 500 after the oscillation cycle T ((b) in FIG. 2). After this reset, the output control circuit 600 passes the output 800 from the PWM controller 500, adds it to the gate of the Pch driver transistor 700, and causes it to operate normally again.

Therefore, if the overcurrent flowing in the output voltage Vout is a temporary (instantaneous) overcurrent caused by noise or the like, it returns to the normal PWM operation after the oscillation cycle T and is continuously excessive due to a device failure or the like. If it is a current, the SR latch circuit 200 is reset by the output of the comparator 100 to protect the Pch driver transistor 700.

(Explanation of limit operation 2) In the above limit operation 1, when the overcurrent flowing in the output voltage Vout is a temporary overcurrent due to noise or the like, the SR latch circuit 200 is temporarily set and the Pch driver transistor 700 is set. However, this limit operation 2 is performed when the H level during the ON period of the oscillation output Lx becomes lower than the constant voltage LMTREF2, which is lower than the constant voltage LMTREF1 (output voltage Vout is short-circuited). The SR latch circuit 400 is set by the output of the comparator 300 to continuously turn off the Pch driver transistor 700 to protect it.

More specifically, as shown in the time chart of FIG. 3, the H level during the ON period of the oscillation output Lx and the constant voltage LMTREF2 lower than the constant voltage LMTREF1 described above are compared by the comparator 300, and the H level during the ON period of the oscillation output Lx is compared. If the level drops below the constant voltage LMTREF2, the output of the comparator 300 sets the SR latch 400.

The output control circuit 600 turns off the Pch driver transistor 700 without passing the output 800 from the PWM controller 500 by the set output of the SR latch 400, and forcibly sets the oscillation output Lx to 0 level. The period during which the SR latch 400 is set (the section of limit operation 2) is shown in (c) in the figure. With this configuration, when an overcurrent flows due to an abnormality such as a short circuit in the output voltage Vout, the Pch driver transistor 700 can be continuously turned off to protect the Pch driver transistor 700 without destroying it. become.

In the above embodiment, in order to perform the limit operation 2, the H level during the ON period of the oscillation output Lx and the constant voltage LMTREF2 are compared by the comparator 300, and the H level during the ON period of the oscillation output Lx is higher than the constant voltage LMTREF2. An example was shown in which the SR latch 400 was set immediately by the output of the comparator 300 when the voltage became low, but as another example, a timer was provided to compare the H level of the oscillation output Lx during the ON period with the constant voltage LMTREF1. Compared with 100, when the H level during the ON period of the oscillation output Lx becomes lower than the constant voltage LMTREF1, the timer is started, the SR latch circuit is set when a predetermined time has elapsed, and the SR latch circuit is set. The output control circuit 600 may be suppressed and controlled by the output.

As another example, the H level during the ON period of the oscillation output Lx is compared with the constant voltage LMTREF1 and the constant voltage LMTREF2, and the number of times the H level during the ON period of the oscillation output Lx is between the constant voltage LMTREF1 and the constant voltage LMTREF2. The SR latch circuit may be set when the number of times reaches a predetermined number, and the output control circuit 600 may be suppressed and controlled by the set output of the SR latch circuit.

The present invention is particularly useful as a power source for portable electronic devices such as mobile phones, PHSs, PDAs, and laptop computers.

<figref num="1">It is a block diagram of the switching regulator which concerns on this Example.</figref><figref num="2">It is a time chart diagram for demonstrating the operation of the switching regulator of FIG. 1 (limit operation 1).</figref><figref num="3">It is a time chart diagram for demonstrating the operation of the switching regulator of FIG. 1 (limit operation 2).</figref><figref num="4">It is a figure for demonstrating the conventional switching regulator (Japanese Patent Laid-Open No. 9-182277).</figref><figref num="5">It is a figure for demonstrating the conventional switching regulator (Japanese Patent Laid-Open No. 9-182277).</figref>

Code description

1: Control unit, Tr1: Output transistor, Tr3: Switching element, L: Coil, 5: Switching regulator, 6: Drive transistor, 7: Diode, 8: Coil, 9: Condenser, 10: Drive circuit, 11: BTL ( Balanced Transformerless) configuration output amplifier, 12 ~ 15: output transistor, 16: voltage detection circuit, 17,18: ground fault detection circuit, 19,20: heaven fault detection circuit, 21: input amplifier, 22: bias circuit, 23 : Stop circuit, Lx: Oscillation output, LMTREF1: Constant voltage (first reference voltage), LMTREF2: Constant voltage (second reference voltage), 100: Comparator (first comparator), 200: SR latch circuit (first reference voltage) 1 SR latch circuit), 300: Comparator (2nd comparator), 400: SR latch circuit (2nd SR latch circuit), 500: PWM controller, 600: Output control circuit, 700: Driver transistor (Pch driver transistor) ), 800: Output from PWM controller (PWM signal), 900: Output from PWM controller (reset signal).