JP2009134387A - High-side switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-side switch and a regulator circuit for detecting short-circuit to a power supply terminal. <P>SOLUTION: A power supply voltage Vdd is applied to an input terminal 102. An external circuit to which a voltage is supplied and an output capacitor Co1 for voltage stabilization are connected to an output terminal 104. An output transistor 10 is arranged between the input terminal 102 and the output terminal 104. A control circuit 12 controls on/off of the output transistor 10. A discharge circuit 20 discharges the output capacitor Co1 connected to the output terminal 104 while the output transistor 10 is turned off. A short-circuit detection comparator 30 compares the potential of the output terminal 104 with a first threshold voltage Vth1 when a prescribed time τ elapses from the start of discharging by a discharge circuit 20. The comparison result is output as a short-circuit detection signal SHRTDET. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a high-side switch, and more particularly to protection of its power supply.

  A high-side switch is used to receive an external power supply voltage Vdd (for example, battery voltage) and supply it to an external circuit via an output terminal, or to cut off the supply (for example, see Patent Document 1). The high-side switch includes, for example, a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) having a power supply voltage applied to one end (source) and the other end (drain) connected to an output terminal. A control signal for controlling on / off is supplied to the control terminal (gate) of the P-channel MOSFET.

  When supplying a voltage to the external circuit, the control signal becomes low level, the P-channel MOSFET is fully turned on, and the power supply voltage is supplied to the external circuit via the output terminal.

JP 2006-155501 A

  Now, let us consider a power fault (also simply referred to as a short circuit) in which the output terminal is short-circuited to the power supply voltage via a path other than the high-side switch. When the high-side switch is fully turned on, the potential of the output terminal becomes equal to the power supply voltage. Therefore, even if the potential of the output terminal is monitored, the presence or absence of a power fault cannot be determined.

  Such a problem may also occur in a regulator circuit that regulates the gate voltage of the high-side switch and stabilizes the output voltage.

  The present invention has been made in view of such a situation, and an object thereof is to provide a high-side switch and a regulator circuit capable of detecting a power fault state.

  A high-side switch according to an aspect of the present invention includes an input terminal to which an external voltage is applied, an output terminal to which an external circuit to which the external voltage is to be supplied and an output capacitor for voltage stabilization are connected, and an input terminal and an output terminal An output transistor provided between the output transistor, a control circuit for controlling the on / off state of the output transistor, a discharge circuit for discharging an output capacitor connected to the output terminal in a state in which the output transistor is off, and a discharge circuit A short-circuit detection comparator that compares the potential of the output terminal with a predetermined first threshold voltage at a timing after the elapse of a predetermined time from the start of discharge.

  When the output terminal is not in a power fault, the potential of the output capacitor is lowered by operating the discharge circuit. However, in the power fault condition, the potential of the output capacitor is maintained near the external voltage even when the discharge circuit is operated. Will remain. Therefore, after discharging the output capacitor for a certain period, the potential can be determined by comparing the potential with the first threshold voltage.

  The high-side switch according to an aspect may further include a timer circuit that measures time and outputs a timing signal that becomes a first level before a predetermined time elapses and a second level after the elapse of a predetermined time. The discharge circuit may discharge the output capacitor when the timing signal is at the first level, and the short circuit detection comparator may latch the result of the voltage comparison when the timing signal is at the second level.

The timer circuit supplies a current to the time constant capacitor for charging, a switch for initializing the potential of the time constant capacitor, and compares the potential of the time constant capacitor with a second threshold voltage corresponding to a predetermined time. And a timer comparator for adjusting at least one of the capacitance value of the time constant capacitor, the second threshold voltage, and the current value supplied by the current source according to the capacitance value of the output capacitor. Also good.
When the capacitance of the output capacitor changes, the time (time constant) required for the potential of the output capacitor to drop due to discharge during a non-sky fault changes. Therefore, by making it possible to adjust the time constant of the timer circuit, it is possible to flexibly cope with changes in the capacitance of the output capacitor.

The output transistor may be set in a state that can be turned on when the potential of the output terminal is lower than the first threshold voltage as a result of voltage comparison by the short-circuit detection comparator.
The circuit can be suitably protected by making the output transistor in a state in which the output transistor can be turned on after confirming that it is in the non-power fault state.

  The high-side switch according to an aspect may shut down at least a part of the circuit when the potential of the output terminal is higher than the first threshold voltage as a result of the voltage comparison by the short-circuit detection comparator.

  The control circuit may include a driver that switches the output transistor on and off.

  The control circuit may include an error amplifier that adjusts the voltage of the control terminal of the output transistor by feedback so that the potential of the output terminal approaches a predetermined target value.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the high-side switch according to the present invention, it is possible to detect a power fault suitably.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are physically directly connected, or the member A and the member B are in an electrically connected state. Including the case of being indirectly connected through other members that do not affect the above.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as an electrical condition. It includes the case of being indirectly connected through another member that does not affect the connection state.

  FIG. 1 is a circuit diagram showing a configuration of a high-side switch 100 according to the embodiment. The high side switch 100 includes an input terminal 102, an output terminal 104, and a short circuit detection terminal 106. An external voltage (hereinafter referred to as power supply voltage Vdd) is input to the input terminal 102 from a battery or a power supply circuit (not shown).

  The output terminal 104 is connected to an external circuit (not shown) to be supplied with the power supply voltage Vdd, and is connected to an output capacitor Co1 for stabilizing the voltage.

  The high-side switch 100 in FIG. 1 outputs an external power supply voltage Vdd to the external circuit (not shown) via the output terminal 104 in the on state, and stops power supply in the off state. On / off of the high side switch 100 is controlled based on an external control signal Scnt. Further, the high-side switch 100 in FIG. 1 detects a power supply fault (short circuit to the power supply terminal 200) of the output terminal 104, and outputs a short circuit detection signal SHRTDET indicating the presence or absence of a short circuit. The short circuit detection signal SHRTDET has a first level (low level) in a short circuit state and a second level (high level) in a non-short circuit state. The short circuit detection terminal 106 is pulled up by a pull-up resistor (not shown). Therefore, the short circuit detection signal SHRTDET is normally high.

  For example, the high side switch 100 is mounted on an in-vehicle audio device or a car navigation system. These devices have a function of receiving power supply voltage Vdd from the battery and supplying power to an antenna installed at a location away from the device, its booster circuit, or a power amplifier that drives a speaker. The high-side switch 100 is used to switch between supplying and shutting off power to a remotely installed circuit. However, the use of the high side switch 100 is not limited to these.

  The high side switch 100 includes an output transistor 10, a control circuit 12, a discharge circuit 20, a short circuit detection comparator 30, and a timer circuit 40.

  The output transistor 10 is provided between the input terminal 102 and the output terminal 104. The output transistor 10 is a P-channel MOSFET, for example, and has a source connected to the input terminal 102 and a drain connected to the output terminal 104.

  The control circuit 12 controls the on / off state of the output transistor 10. Specifically, the control circuit 12 includes a driver that controls the gate voltage Vg of the output transistor 10 with two values of high level and low level. The control circuit 12 sets the gate voltage Vg of the output transistor 10 to the ground voltage when the control signal Scnt instructs to turn on the output transistor 10, and sets the gate voltage Vg to the power supply voltage Vdd when instructing to turn it off.

  The discharge circuit 20 discharges the output capacitor Co1 connected to the output terminal 104 when the output transistor 10 is turned off.

  The short-circuit detection comparator 30 compares the potential Vx of the output terminal 104 with a predetermined first threshold voltage Vth1 at a timing after the elapse of a predetermined time τ from the start of discharge by the discharge circuit 20.

The timer circuit 40 measures time, and outputs a timing signal TS that becomes a first level (low level) before a predetermined time elapses and becomes a second level (high level) after elapses.
The timer circuit 40 includes a timer comparator 42, a current source 44, and a switch 46. The current source 44 charges the time constant capacitor Ct externally attached to the capacitor terminal 108 by supplying the current Ic2. The switch 46 initializes the potential Vy of the time constant capacitor Ct when turned on. The timer comparator 42 compares the potential Vy of the time constant capacitor Ct with the second threshold voltage Vth2 corresponding to the predetermined time τ.

  For example, the switch 46 is turned off at the start timing of the short circuit detection operation instructed by the standby signal STB. The start timing may be triggered by power-on of an electronic device including the high side switch 100.

When the switch 46 is turned off, the potential Vy of the time constant capacitor Ct is increased by the constant current Ic2, and reaches the second threshold voltage Vth2 after a predetermined time τ. In other words, the second threshold voltage Vth2 is
Vth2 = Ic2 × τ / Ct
It is set to satisfy.

  The timer circuit 40 is configured such that at least one of the capacitance value of the time constant capacitor Ct, the second threshold voltage Vth2, and the current value Ic2 supplied from the current source 44 can be adjusted according to the capacitance value of the output capacitor Co1. The In this case, the predetermined time τ can be adjusted.

  The discharge circuit 20 discharges the output capacitor Co1 when the timing signal TS is at the first level (low level). When the timing signal TS becomes the second level (high level), the short-circuit detection comparator 30 performs the voltage comparison described above and latches the comparison result.

  The discharge circuit 20 includes an inverter 22, a switch 24, and a current source 26. The inverter 22 inverts the timing signal TS. The switch 24 is turned on when the timing signal * TS inverted by the inverter 22 is at a high level, that is, before the predetermined time τ has elapsed. When the switch 24 is turned on, the output capacitor Co1 is discharged by the constant current Ic1 generated by the current source 26. When the predetermined time τ elapses, the switch 24 is turned off and the discharge is stopped.

  The output transistor 10 is set to an ON state when the voltage Vx of the output terminal 104 is lower than the first threshold voltage Vth1 as a result of the voltage comparison by the short circuit detection comparator 30. For this purpose, the short circuit detection signal SHRTDET output from the short circuit detection comparator 30 is supplied to the control circuit 12. The control circuit 12 becomes inactive when the short circuit detection signal SHRTDET is at a low level indicating a short circuit state, and is set to be active when the short circuit detection signal SHRTDET is at a high level indicating a non-short circuit state.

  The high-side switch 100 shuts down at least a part of the circuit when the voltage Vx of the output terminal 104 is higher than the first threshold voltage Vth1 as a result of the voltage comparison by the short-circuit detection comparator 30. Thereby, power consumption can be reduced.

  The above is the configuration of the high-side switch 100. Next, the operation of the high side switch 100 will be described. 2A and 2B are time charts showing the operation of the high-side switch 100 of FIG.

FIG. 2A shows the operation at the normal time (when not short-circuited), and FIG. 2B shows the operation at the time of short-circuit.
First, the normal operation will be described. When the standby signal STB becomes high level at time t0, the timer circuit 40 starts, and the timing signal TS becomes high level at time t1 after a predetermined time τ has elapsed. During time t0 to t1, the discharge circuit 20 discharges the output capacitor Co1, and the voltage Vx decreases. At time t1, since Vx <Vth1, the short circuit detection signal SHRTDET indicating the comparison result by the short circuit detection comparator 30 becomes high level, and the value is latched. Then, a high-level short-circuit detection signal SHRTDET indicating that no short-circuit has occurred is output to the outside of the high-side switch 100.

  In response to the high-level short-circuit detection signal SHRTDET, the control circuit 12 turns on the output transistor 10. As a result, the potential Vx of the output capacitor Co1 becomes the power supply voltage Vdd and is supplied to the external circuit.

  Next, the operation at the time of short circuit will be described. The standby signal STB becomes high level at time t0, and the timing signal TS becomes high level at time t1 after a predetermined time τ has elapsed. During time t0 to t1, the discharge circuit 20 discharges the output capacitor Co1, but since the output capacitor Co1 is connected to the power supply terminal 200, the voltage Vx is fixed near the power supply voltage Vdd. Since Vx> Vth1 at time t1, the short circuit detection signal SHRTDET indicating the comparison result by the short circuit detection comparator 30 becomes low level, and the value is latched. Then, a low level short circuit detection signal SHRTDET indicating a short circuit state is output to the outside of the high side switch 100.

  In response to the low-level short-circuit detection signal SHRTDET, the control circuit 12 continues to turn off the output transistor 10. However, even if the output transistor 10 is turned off, since the output terminal 104 is in a power fault, the voltage Vx continues to be fixed at the power supply voltage Vdd. Thereafter, at time t2, the standby signal STB is set to a low level, and the circuit is reset.

The above is the operation of the high-side switch 100.
According to the high side switch 100 according to the present embodiment, it is possible to suitably detect a short circuit (power fault) with respect to the power supply terminal.

  For example, if the high-side switch 100 is used in a vehicle-mounted device, the user can be notified that a power fault has occurred. When the power supply voltage Vdd is distributed to a plurality of routes, if the high-side switch 100 of FIG. 1 is provided for each route, it becomes easy to specify which route has a power fault, and Maintenance becomes easy. Battery consumption can be prevented.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there. Hereinafter, such modifications will be described.

  In the embodiment, the case where the output transistor 10 is used as a switch in two stages of on and off has been described, but the present invention is not limited to this. The high side switch 100 may constitute a regulator circuit. In this case, the control circuit 12 may include an error amplifier that adjusts the voltage (gate voltage Vg) of the control terminal of the output transistor 10 by feedback so that the potential Vx of the output terminal 104 approaches a predetermined target value. Even when the high-side switch 100 is a regulator, it is possible to detect the power fault suitably.

  The setting of the high level and low level of the logic signal in the circuit described in the embodiment is merely an example, and may be reversed as appropriate. Further, replacement of MOSFET and bipolar transistor, replacement of N channel and P channel are also included in the scope of the present invention.

  Although the present invention has been described using specific words and phrases based on the embodiments, the embodiments are merely illustrative of the principles and applications of the present invention, and the embodiments are defined in the claims. Many modifications and arrangements can be made without departing from the spirit of the present invention.

It is a circuit diagram which shows the structure of the high side switch which concerns on embodiment. 2A and 2B are time charts showing the operation of the high-side switch of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... High side switch, 102 ... Input terminal, 104 ... Output terminal, 106 ... Short circuit detection terminal, 108 ... Capacitor terminal, 10 ... Output transistor, 12 ... Control circuit, 20 ... Discharge circuit, 22 ... Inverter, 24 ... Switch, 26 ... Current source, 30 ... Short circuit detection comparator, 40 ... Timer circuit, 42 ... Timer comparator, 44 ... Current source, 46 ... Switch, Co1 ... Output capacitor, Scnt ... Control signal, TS ... Timing signal, SHRTDET ... Short circuit detection Signal, Vth1... First threshold voltage, Vth2... Second threshold voltage.

Claims (7)

An input terminal to which an external voltage is applied;
An output terminal to which the external circuit to be supplied with the external voltage and an output capacitor for voltage stabilization are connected;
An output transistor provided between the input terminal and the output terminal;
A control circuit for controlling the on / off state of the output transistor;
A discharge circuit for discharging the output capacitor connected to the output terminal in a state where the output transistor is off;
A short-circuit detection comparator that compares the potential of the output terminal with a predetermined first threshold voltage at a timing after a predetermined time has elapsed from the start of discharge by the discharge circuit;
A high-side switch characterized by comprising: A timer circuit for measuring a time and outputting a timing signal that becomes a first level before the predetermined time elapses and a second level after elapses;
The discharge circuit discharges the output capacitor when the timing signal is at the first level;
The high-side switch according to claim 1, wherein the short-circuit detection comparator latches a result of voltage comparison when the timing signal becomes the second level. The timer circuit is
A current source for supplying and charging a current to the time constant capacitor;
A switch for initializing the potential of the time constant capacitor;
A timer comparator for comparing the potential of the time constant capacitor with a second threshold voltage corresponding to the predetermined time;
And at least one of the capacitance value of the time constant capacitor, the second threshold voltage, and the current value supplied by the current source can be adjusted according to the capacitance value of the output capacitor. The high-side switch according to claim 2, wherein the switch is a high-side switch.   2. The output transistor is set to an on-state when the potential of the output terminal is lower than the first threshold voltage as a result of voltage comparison by the short-circuit detection comparator. High side switch.   2. The high-side switch according to claim 1, wherein when a potential of the output terminal is higher than the first threshold voltage as a result of voltage comparison by the short-circuit detection comparator, at least a part of the circuit is shut down.   The high-side switch according to claim 1, wherein the control circuit includes a driver that switches on and off of the output transistor.   2. The high side according to claim 1, wherein the control circuit includes an error amplifier that adjusts the voltage of the control terminal of the output transistor by feedback so that the potential of the output terminal approaches a predetermined target value. switch.

Images