JP2004254021A - Method for protecting amplifier, and semiconductor device provided with amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain a suspended state until a short-circuit state is removed by surely detecting the shor-circuit state of an amplifier and stopping (suspending) power supply, in short-circuit protection of the amplifier. <P>SOLUTION: The output potential of the amplifier is compared with a detection potential obtained by biasing a power source potential only by a prescribed value, and when the output potential reaches the detection potential, a comparison output is generated. When the comparison output is generated over a prescribed time or more, the operation power source of the amplifier is stopped. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a protection method for a short-circuit fault on the output side of an amplifier such as a power amplifier, and a semiconductor device having an amplifier circuit with a short-circuit protection circuit.
[0002]
[Prior art]
2. Description of the Related Art In an electronic device such as a personal computer, a PDA, a PDC, and a mobile phone, a speaker amplifier and a headphone amplifier are provided on the output side. If the output terminal is short-circuited to a power supply potential point or a ground potential point inside or outside of these electronic devices, an overcurrent flows, and the power transistor for output or the like is overheated and destroyed.
[0003]
There are various protection methods for detecting such a short-circuit fault and protecting the electronic device. For example, in the temperature detection protection method, a temperature detection element is provided near an element to be protected, a temperature rise due to an overcurrent is detected, and when a temperature equal to or higher than a predetermined value is reached, a power supply of the electronic device is turned on. Protection is provided by cutting. The current detection and protection method includes a method in which a protection element such as a fuse (eg, an IC protector) is provided in a current path to be protected, and the protection element is blown by an overcurrent. There is a method of protecting the electronic device by cutting off the power supply of the electronic device when the above current flows (see Patent Document 1). The voltage detection and protection method detects a potential at a location to be protected, detects a potential state that does not occur in a normal state, determines that a short-circuit has occurred, and turns off the power of the electronic device to protect the electronic device ( See Patent Document 2).
[0004]
[Patent Document 1]
JP 2001-333528 A [Patent Document 2]
JP 2001-339289 A
[Problems to be solved by the invention]
However, according to the conventional temperature detection protection method, when the temperature of a protected element such as an output transistor becomes abnormally high, the power supply is stopped (suspended) to protect the element. It takes time from the occurrence of the error until it is actually protected. It is not uncommon for the output transistor to break down during this time. Further, when the suspension is applied, the temperature decreases, and when the suspension is released, an overcurrent flows again. The suspension and its release are repeatedly performed until the cause of the abnormality is removed, and the repetitive stress may cause the protected element to eventually break down.
[0006]
Further, among the current detection and protection methods, those using a protection element such as an IC protector cannot be used again once the overcurrent flows and melts, and the price is relatively expensive. On the other hand, in a device such as Patent Document 1 in which the switch means is turned off when a current equal to or more than a predetermined value flows to suspend the device, the protection component (such as an IC protector) can be used many times without replacement. However, the suspension stops the overcurrent and the suspension is released and the overcurrent flows again. In order to avoid such a state, it is necessary to maintain the state once suspended and to cancel the suspension by separately giving a suspend release instruction.
[0007]
Further, in the conventional voltage detection and protection method as disclosed in Patent Literature 2, a short-circuit fault is determined by detecting a potential state that does not occur in a normal state. Although it reaches the vicinity of the potential point, it cannot be applied to short-circuit protection.
[0008]
Accordingly, the present invention provides a short-circuit protection method for an amplifier that reliably detects a short-circuit state of an amplifier, stops power supply (suspend), and maintains the suspended state until the short-circuit state is removed, and an amplifier with a short-circuit protection circuit. It is an object to provide a semiconductor device provided with a circuit.
[0009]
[Means for Solving the Problems]
2. The method of claim 1, wherein the output potential of the amplifier is deviated from the first power supply potential by a first predetermined value and the second detection is deviated from the second power supply potential by a second predetermined value. A comparison output is generated when the output potential reaches the first detection potential or the second detection potential, and a comparison output is generated when the comparison output is generated for a predetermined time or more. The operation power supply is stopped.
[0010]
3. The semiconductor device according to claim 2, wherein the operation power supply is stopped in response to the control signal, and the output potential of the amplifier and the first detection potential and the second power supply potential deviated from the first power supply potential by a first predetermined value. A comparison means for comparing a second detection potential deviated from the first detection potential by a second predetermined value to generate a comparison output when the output potential reaches the first detection potential or the second detection potential; Only during the occurrence of, the charging means for charging the external capacitor via the connection terminal, and stop control means for generating the control signal when the potential of the connection terminal reaches a predetermined threshold, It is characterized by having.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a semiconductor device including a short-circuit protection method for an amplifier and an amplifier circuit with a short-circuit protection circuit according to the present invention will be described with reference to the drawings.
[0012]
FIG. 1 is a diagram illustrating a configuration of a semiconductor device 10 including an amplifier circuit with a short-circuit protection circuit according to a first embodiment of the present invention. 2A and 2B are diagrams for explaining the operation of the present invention.
[0013]
In FIG. 1, a power amplifier (hereinafter, power amplifier) 11 operates with a voltage between a first power supply potential (hereinafter, simply power supply potential) Vcc and a second power supply potential (hereinafter, ground potential) Vgnd, and an input signal Vin. And outputs an output signal Vout.
SP denotes a speaker, which is driven by the output signal Vout with reference to the potential Vcc / 2.
[0014]
The output section of the power amplifier 11 has two transistors connected in series between the power supply potential Vcc and the ground potential Vgnd and driven by push-pull, and an output signal Vout is taken out from the series connection point. . Therefore, although the output signal Vout has a voltage drop due to the on-resistance of the transistor and the flowing current, the output signal Vout swings to a value close to the power supply potential Vcc or the ground potential Vgnd.
[0015]
The first comparator 12-1 compares the output signal Vout with a first threshold potential (Vcc-Vth) lower than the power supply potential Vcc by the offset voltage Vth, and outputs a comparison output when the output signal Vout becomes higher than the first threshold voltage. appear. The second comparator 12-2 compares the output signal Vout with a second threshold potential (Vth + Vgnd) higher than the ground potential Vgnd by the offset voltage Vth, and generates a comparison output when the output signal Vout becomes lower than the second threshold voltage. . When the power supply potential Vcc point or the ground potential Vgnd point and the output signal Vout point are short-circuited (eg, F in FIG. 1), the deviation voltage Vth has a magnitude in consideration of a voltage drop due to the short-circuit impedance. Is set.
[0016]
When a comparison output is generated in either the first comparator 12-1 or the second comparator 12-2, the integration circuit 13 outputs a start signal to the charging circuit 14. The charging circuit 14 has a switch and a current source, and charges the external capacitor Ct while there is a start signal from the integrated circuit 13. Rt is a discharge resistance. The charging circuit 14 may be provided with a discharging circuit for quickly discharging the charge of the capacitor Ct. In this case, the resistor Rt can be omitted.
[0017]
When the charge potential of the capacitor Ct reaches a predetermined threshold, the suspend control circuit 15 generates an output signal and turns off the switch circuit 16. The switch circuit 16 is for turning on / off an operation power supply for operating the power amplifier 11, and is kept off as long as there is an output signal of the suspend control circuit 15. The constant current source 19 is a reference current source for the operation of the power amplifier 11.
[0018]
The thermal shutdown circuit 17 is arranged near the output of the power amplifier 11, generates a detection signal indicating the temperature of the output of the power amplifier 11, and supplies the signal to the suspend control circuit 18. When the supplied detection signal reaches a predetermined threshold, the suspend control circuit 18 generates an output signal, and also turns off the switch circuit 16. The thermal shutdown circuit 17 and the suspend control circuit 18 are provided for backup protection, although their detection operations are slower than those based on potential detection.
[0019]
The operation of the amplifier circuit with a short-circuit protection circuit of FIG. 1 will be described with reference to FIGS. 2 (a) and 2 (b).
[0020]
FIGS. 2A and 2B are diagrams illustrating a state where the output signal Vout is output from the power amplifier 11 at the maximum output amplitude. FIG. 6A is a characteristic diagram when the load is heavy, that is, when the output current is large. In this case, the voltage drop due to the product of the on-resistance of the transistor of the power amplifier 11 and the output current increases. Therefore, since this voltage drop becomes larger than the deviation voltage Vth, no comparison output is generated from the first comparator 12-1 and the second comparator 12-2.
[0021]
On the other hand, FIG. 6B is a characteristic diagram when the load is light, that is, when the output current is small. In this case, the voltage drop due to the product of the on-resistance of the transistor of the power amplifier 11 and the output current is small. Therefore, since this voltage drop is smaller than the deviation voltage Vth, a time period occurs in which the output signal Vout is higher than the first threshold potential (Vcc-Vth) and lower than the second threshold potential (Vth + Vgnd). During these times, the first comparator 12-1 and the second comparator 12-2 generate comparison outputs.
[0022]
The duration of the comparison output from the first comparator 12-1 and the second comparator 12-2 is always shorter than the half cycle of the lowest frequency in the frequency band used by the power amplifier 11. Therefore, the time from the start of charging of the capacitor Ct until the charging potential reaches the predetermined threshold value of the suspend control circuit 15 is set to be longer than the half cycle of the lowest frequency, that is, the duration of the comparison output. By performing this time setting, when the output signal Vout has the maximum output amplitude, even if the comparison output from the first comparator 12-1 and the second comparator 12-2 occurs, the suspend control circuit 15 outputs No signal is generated, so the switch circuit 16 does not turn off. Therefore, erroneous determination of a short-circuit failure can be avoided.
[0023]
Now, it is assumed that a short-circuit fault occurs between the point of the output signal Vout and the point of the power supply potential Vcc as shown in FIG. 1F. In this case, a large short-circuit current flows from the power supply potential Vcc through the output signal Vout via the transistor at the output of the power amplifier 11.
[0024]
The magnitude of the deviation voltage Vth is set in consideration of a voltage drop due to a short-circuit impedance at the time of a short-circuit failure. Therefore, the potential at the point of the output signal Vout becomes higher than the first threshold potential (Vcc-Vth).
[0025]
Then, a comparison output is generated from the first comparator 12-1, and the charging circuit 14 is activated via the integration circuit 13. When the capacitor Ct is charged and its charged potential reaches a predetermined threshold of the suspend control circuit 15, the switch circuit 16 is turned off and the operation of the power amplifier 11 is stopped. As a result, the transistor at the output of the power amplifier 11 is turned off, and the short-circuit current is cut off. Therefore, it is possible to prevent the circuit elements including the transistor at the output section of the power amplifier 11 from being destroyed due to the short-circuit failure.
[0026]
Further, in the present invention, even if the transistor at the output section of the power amplifier 11 is turned off and the short-circuit current is cut off, the potential of the output signal Vout point is still higher than the first threshold potential (Vcc-Vth). Therefore, the switch circuit 16 continues to be turned off. Then, when the short-circuit fault is removed, the normal operation state is automatically restored.
[0027]
The same operation is performed when a short circuit fault occurs between the output signal Vout point and the ground potential Vgnd point.
[0028]
Such a short-circuit failure often occurs when the wiring to the speaker SP or the like is sandwiched between the folded portions of the body case when repairing or adjusting a foldable electronic device such as a notebook computer. In this case, according to the present invention, even if a short-circuit failure occurs during the repair, it can be appropriately protected, so that no fatal damage is caused. Therefore, the present invention is suitable for such a foldable electronic device.
[0029]
FIG. 3 is a diagram illustrating a configuration of a semiconductor device 20 including an amplifier circuit with a short-circuit protection circuit according to a second embodiment of the present invention. In the second embodiment, the speaker SP is driven by balanced tide load (BTL) using two inverting amplifiers 21-1 and 21-2.
[0030]
In FIG. 3, the first power amplifier 21-1 inverts and amplifies the input signal Vin and outputs a first output signal Vout1. The second power amplifier 21-2 receives the first output signal Vout1 as an input signal, inverts and amplifies the signal, and outputs a second output signal Vout2. Therefore, the first output signal Vout1 and the second output signal Vout2 have an opposite phase relationship, and the speaker SP is driven with a larger amplitude. Note that resistors R1 and R3 are input resistors, and resistors R2 and R4 are feedback resistors.
[0031]
In addition, a first comparator 22-1 and a second comparator 22-2 are provided to detect the potential at the first output signal Vout1 point, and to detect the potential at the second output signal Vout2 point. , A third comparator 22-3, and a fourth comparator 22-4.
The comparison outputs of the first to fourth comparators 22-1 to 22-4 are supplied to the integration circuit 23.
[0032]
The integrated circuit 23, charging circuit 24, suspend control circuit 25, switch circuits 26-1 and 26-2, thermal shutdown circuit 27, suspend control circuit 28, and constant current sources 29-1 and 29-2 in FIG. 1 corresponds to the integrated circuit 13, the charging circuit 14, the suspend control circuit 15, the switch circuit 16, the thermal shutdown circuit 17, the suspend control circuit 18, and the constant current source 19 in FIG. The same components as those in FIG. 1 are denoted by the same symbols.
[0033]
In the semiconductor device 20 of FIG. 3 that drives the speaker SP by the BTL, the first output signal Vout1 and the second output signal Vout2 are short-circuited to the power supply potential Vcc point or the ground potential Vgnd point at the second output signal Vout2 point. As in the first embodiment, appropriate protection can be provided.
[0034]
FIG. 4 is a diagram illustrating a configuration of a semiconductor device 30 including an amplifier circuit with a short-circuit protection circuit according to a third embodiment of the present invention. In the third embodiment, the two speakers SP1 and SP2 are each driven by BTL. For this purpose, FIG. 4 further includes a third power amplifier 31-3 and a fourth power amplifier 31-4 as compared with FIG.
[0035]
The third power amplifier 31-3 inverts and amplifies the second input signal Vin2 and outputs a third output signal Vout3. The fourth power amplifier 31-4 receives the third output signal Vout3 as an input signal, inverts and amplifies it, and outputs a fourth output signal Vout4. Therefore, the third output signal Vout3 and the fourth output signal Vout4 have an opposite phase relationship, and the speaker SP is driven with a larger amplitude. Note that resistors R5 and R7 are input resistors, and resistors R6 and R8 are feedback resistors.
[0036]
A first multi-input comparator 32-1 and a second multi-input comparator 32-2 are provided to detect potentials at the first output signal Vout1 to the fourth output signal Vout4.
[0037]
The first multi-input comparator 32-1 inputs the first output signal Vout1 to the fourth output signal Vout4 to the positive input terminal, and inputs the first threshold voltage (Vcc-Vth) to the negative input terminal. . The first multi-input comparator 32-1 generates a comparison output when any one of the first output signal Vout1 to the fourth output signal Vout4 exceeds the first threshold voltage (Vcc-Vth).
The second multiple-input comparator 32-2 inputs the first output signal Vout1 to the fourth output signal Vout4 to the negative input terminal, and inputs the second threshold voltage (Vth + Vgnd) to the positive input terminal. The second multi-input comparator 32-2 generates a comparison output when any one of the first output signal Vout1 to the fourth output signal Vout4 falls below the second threshold voltage (Vth + Vgnd). These first and second multi-input comparators 32-1 and 32-2 also have the functions of the comparator and the coupling circuit in FIGS.
[0038]
The comparison outputs of the first and second multi-input comparators 32-1 and 32-2 are supplied to the charging circuit 34.
[0039]
The charging circuit 34 and the suspend control circuit 35 in FIG. 4 correspond to the charging circuit 24 and the suspend control circuit 25 in FIG. 3, respectively, and perform the same operations. The same components as those in FIG. 1 are denoted by the same symbols.
[0040]
FIG. 4 specifically shows a switch circuit that controls on / off of the first to fourth power amplifiers 31-1 to 31-4.
[0041]
That is, a constant current source 39-4, an NPN transistor (hereinafter, NPN) 39-2 and a resistor R9 are connected in series between the power supply potential Vcc and the ground potential Vgnd, and the NPN 39-3 and the resistor R10 Are connected in series. The base of NPN 39-2 is connected to the emitter of NPN 39-3, and the collector of NPN 39-2 is connected to the base of NPN 39-3. The switch NPN 39-1 is connected between the collector of the NPN 39-2 and the ground potential Vgnd, and the output signal of the suspend control circuit 35 is supplied to the base of the NPN 39-1.
[0042]
Also, NPNs 36-1 to 36-4 for on / off control of the power amplifiers 31-1 to 31-4 and resistors R11 to R14 are provided in series between each power amplifier and the ground. The potential of the resistor R10 is supplied to the bases of the NPNs 36-1 to 36-4.
[0043]
Since the switch circuit is configured as described above, the NPNs 36-1 to 36-4 are always on. When a short-circuit fault occurs, NPNs 36-1 to 36-4 are all turned off, and all power amplifiers 31-1 to 31-4 stop operating.
[0044]
Therefore, also in the third embodiment shown in FIG. 4, short-circuit faults can be appropriately protected as in the first and second embodiments. In addition, short-circuit protection can be performed in common even in a device including a large number of power amplifiers.
[0045]
【The invention's effect】
According to the present invention, a short-circuit fault of an amplifier is detected by being clearly distinguished from an output signal which swings to near upper and lower power supply potentials by using both the output potential and time. Therefore, short-circuit protection of an amplifier that generates an output signal that swings to the vicinity of the power supply potential can be performed by potential detection, which has been conventionally difficult.
[0046]
Further, since the short-circuit failure is determined by the output potential, the operating power supply of the amplifier is continuously stopped until the cause of the abnormality is removed. Therefore, the stop and its release unlike the related art are not repeated. Further, when the cause of the abnormality is removed, the amplifier automatically returns to the operating state.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a semiconductor device 10 including an amplifier circuit according to a first embodiment.
FIG. 2 is a diagram illustrating the operation of the present invention.
FIG. 3 is a configuration diagram of a semiconductor device 20 including an amplifier circuit according to a second embodiment.
FIG. 4 is a configuration diagram of a semiconductor device 30 including an amplifier circuit according to a third embodiment.
[Explanation of symbols]
10, 20, 30 Semiconductor devices 11, 21-1, 21-2, 31-1 to 31-4 provided with amplifier circuits Power amplifiers 12-1, 12-2, 22-1 to 22-4 Comparator 32- 1, 32-2 Multi-input comparators 13, 23 Integrated circuits 14, 24, 34 Charge circuits 15, 18, 25, 28, 35 Suspend control circuits 16, 26-1, 26-2 Switch circuits 17, 27 Thermal shutdown circuits SP, SP1, SP2 Speaker Ct Capacitor Rt Resistance Vin, Vin1, Vin2 Input signal Vout, Vout1 to Vout4 Output signal Vcc Power supply potential Vgnd Ground potential Vth Deviation voltage

Claims (2)

Comparing the output potential of the amplifier with a first detection potential deviated from the first power supply potential by a first predetermined value and a second detection potential deviated from the second power supply potential by a second predetermined value;
Generating a comparison output when the output potential reaches the first detection potential or the second detection potential;
When the comparison output is generated for a predetermined time or more, the operation power supply of the amplifier is stopped, and a short-circuit protection method for the amplifier is provided. An amplifier whose operation power supply is stopped according to a control signal;
Comparing the output potential of the amplifier with a first detection potential deviated from a first power supply potential by a first predetermined value and a second detection potential deviated from a second power supply potential by a second predetermined value; Comparing means for generating a comparison output when the first detection potential or the second detection potential is reached;
Charging means for charging an external capacitor via a connection terminal only while the comparison output is being generated;
A stop control unit that generates the control signal when the potential of the connection terminal reaches a predetermined threshold.

Images