JP2001339289A - Short protecting circuit for semiconductor integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a short protecting circuit for a semiconductor integrated circuit which prevents an overcurrent from flowing to an output terminal if the output terminal short-circuits to a ground level in error. SOLUTION: This circuit is equipped with a 1st transistor (TR) (Q2) which turns off when the level at an output terminal (50) as an external terminal of the semiconductor integrated circuit varies to below a threshold from a ground level and a 2nd TR (Q4) which turns on when the 1st TR (Q2) turns off, cuts off the operating power supply of an output circuit (45) outputting a signal from the output terminals (50), so when the output terminal (50) reaches the ground level or its nearby level, the 1st TR (Q2) turns off and the 2nd TR (Q4) turns on to cut off the operating power supply to the output circuit (45) and then an overcurrent from flowing from the output circuit to the output terminals (50) is prevented, thereby protecting the output circuit (45).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a short-circuit protection circuit for a semiconductor integrated circuit, and more particularly to a short-circuit protection circuit for a semiconductor integrated circuit that prevents an overcurrent from flowing when an output terminal of the semiconductor integrated circuit is short-circuited.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing an example of a conventional video signal output driver circuit. This output driver circuit is a semiconductor integrated circuit. In the figure, the emitter of a pnp transistor Q3 which is supplied with a bias and operates as a constant current source is connected to a power supply Vcc via a resistor R2, and the collector of the transistor Q3 is connected to the collector and base of an npn transistor Q5. Transistor Q
5 are npn transistors Q7, Q12, Q13
Are connected in common to a base of a current mirror circuit.

The emitters of the transistors Q5 and Q7 are grounded (GND) via the resistors R3 and R5, respectively. The collector of the transistor Q7 is connected to the collector and the base of the pnp transistor Q6. The transistor Q6 has an emitter connected to the power supply Vcc and a base commonly connected to the bases of the pnp transistors Q14 and Q15 to form a current mirror circuit.

The npn transistors Q10 and Q11 form a differential circuit, and a video signal is input from an input terminal 10 to the base of the transistor Q10. Transistors Q10 and Q11 have a collector connected to a pnp transistor Q8,
The collector is connected to the collector of Q9, the emitter is connected to the collectors of npn transistors Q12 and Q13, and the resistor is connected by an open gain adjustment resistor R8.
The transistors Q8 and Q9 have their emitters connected to the power supply Vcc via the resistors R9 and R10, their bases connected in common and connected to the collector of the transistor Q8 to form a current mirror circuit, and the load of the transistors Q10 and Q11. Is composed. The emitters of the transistors Q12 and Q13 as constant current sources are grounded via resistors R6 and R7.

A transistor Q for taking out the connection of the differential circuit
11 is a pn which constitutes an emitter follower circuit.
It is connected to the bases of p transistors Q16 and Q17. The transistor Q16 has a collector grounded and an emitter connected to the collector of the pnp transistor Q14 and the base of the npn transistor Q18. The emitter of transistor Q14 is connected to power supply Vcc.
The transistor Q17 has a collector connected to an npn transistor Q.
20 is connected to the collector and base, and the emitter is pn.
It is connected to the collector of the p transistor Q15 and the collector and base of the npn transistor Q19. The emitter of transistor Q15 is connected to power supply Vcc.

The transistor Q18 has a collector connected to the power supply Vc.
c, and the emitter is connected to the emitter of the transistor Q19, the collector of the npn transistor Q21, and the output terminal 20 to form an emitter follower circuit. The transistor Q20 has a collector and a base connected to the base of the transistor Q21, an emitter of the transistor Q20 is grounded via a resistor R13, and an emitter of the transistor Q21 is grounded to form a current mirror circuit.

The output terminal 20 is connected to the base of a transistor Q11 via a feedback resistor R12. The base of the transistor Q11 is connected to the reference voltage Vr via the resistor R11.
ef is applied to the terminal 30 and is connected to the collector of the transistor Q11 via the phase correcting capacitor C1.

[0008]

In the above conventional circuit,
When the output terminal 20, which is an external terminal of the semiconductor integrated circuit, is erroneously short-circuited to the ground (GND) level, the power supply Vcc
Overcurrent flows to the ground level through the transistor Q18 and the output terminal 20 to generate heat. Further, since several to several tens of the video signal output driver circuits are integrated in the semiconductor integrated circuit, if the output terminals 20 of a plurality of video signal output driver circuits are erroneously short-circuited to the ground level, There has been a problem that the package of the semiconductor integrated circuit may be overheated.

The present invention has been made in view of the above points, and provides a short-circuit protection circuit for a semiconductor integrated circuit that prevents an overcurrent from flowing to an output terminal when the output terminal is short-circuited to a ground level by mistake. The purpose is to:

[0010]

According to the first aspect of the present invention, there is provided an output terminal (50) which is an external terminal of a semiconductor integrated circuit.
A first transistor (Q2) that turns off when the level of the first transistor (Q2) becomes lower than the threshold value from the ground level, and turns on the output terminal (5) by turning off the first transistor (Q2).
And a second transistor (Q4) for shutting off the operating power supply of the output circuit (45) for outputting a signal from the output circuit (0).

As described above, when the output terminal (50) is at or near the ground level, the first transistor (Q2) is turned off and the second transistor (Q4) is turned on. The operation power supply of (45) is cut off to prevent an overcurrent from flowing from the output circuit to the output terminal (50), and the output circuit (45) can be protected.

The reference numerals in the parentheses are provided for easy understanding, are merely examples, and are not limited to the illustrated embodiment.

[0013]

FIG. 1 is a circuit diagram of an embodiment of a video signal output driver circuit to which the circuit of the present invention is applied. This output driver circuit is formed as a semiconductor integrated circuit, and the same reference numerals in FIG.

In FIG. 1, an emitter of a pnp transistor Q1 which is supplied with a bias to its base and operates as a constant current source is connected to a power supply Vcc via a resistor R1, and a collector of the transistor Q1 has a collector of an npn transistor Q2 and an npn transistor. It is connected to the base of Q4. Transistor Q2 has its emitter grounded and its base connected to output terminal 50 via resistor R4. The collector of the transistor Q4 is commonly connected to the collector of the npn transistor Q5, and the emitter of the transistor Q4 is grounded. The above transistors Q1, Q
2, Q4 and the resistors R1 and R4 constitute the short-circuit protection circuit 40.

In the output driver circuit 45, the emitter of a pnp transistor Q3 which is supplied with a bias to its base and operates as a constant current source is connected to a power supply Vcc via a resistor R2, and the collector of the transistor Q3 is connected to the collector of an npn transistor Q5. The base of the transistor Q5 is connected to an npn transistor Q7, Q12, Q
13 are commonly connected to each other to form a current mirror circuit.

The emitters of the transistors Q5 and Q7 are grounded (GND) via the resistors R3 and R5, respectively. The collector of the transistor Q7 is connected to the collector and the base of the pnp transistor Q6. The transistor Q6 has an emitter connected to the power supply Vcc and a base commonly connected to the bases of the pnp transistors Q14 and Q15 to form a current mirror circuit.

The npn transistors Q10 and Q11 form a differential circuit, and a video signal is input from an input terminal 10 to the base of the transistor Q10. Transistors Q10 and Q11 have a collector connected to a pnp transistor Q8,
The collector is connected to the collector of Q9, the emitter is connected to the collectors of npn transistors Q12 and Q13, and the resistor is connected by an open gain adjustment resistor R8.
The transistors Q8 and Q9 have their emitters connected to the power supply Vcc via the resistors R9 and R10, their bases connected in common and connected to the collector of the transistor Q8 to form a current mirror circuit, and the load of the transistors Q10 and Q11. Is composed. The emitters of the transistors Q12 and Q13 as constant current sources are grounded via resistors R6 and R7.

Transistor Q for taking out connection of differential circuit
11 is a pn which constitutes an emitter follower circuit.
It is connected to the bases of p transistors Q16 and Q17. The transistor Q16 has a collector grounded and an emitter connected to the collector of the pnp transistor Q14 and the base of the npn transistor Q18. The emitter of transistor Q14 is connected to power supply Vcc.
The transistor Q17 has a collector connected to an npn transistor Q.
20 is connected to the collector and base, and the emitter is pn.
It is connected to the collector of the p transistor Q15 and the collector and base of the npn transistor Q19. The emitter of transistor Q15 is connected to power supply Vcc.

The transistor Q18 has a collector connected to the power supply Vc.
c, the emitter is connected to the emitter of the transistor Q19, the collector of the npn transistor Q21, and the output terminal 50 to form an emitter follower circuit. The transistor Q20 has a collector and a base connected to the base of the transistor Q21, an emitter of the transistor Q20 is grounded via a resistor R13, and an emitter of the transistor Q21 is grounded to form a current mirror circuit.

The output terminal 50 is connected to the base of the transistor Q11 via the feedback resistor R12. The base of the transistor Q11 is connected to the reference voltage Vr via the resistor R11.
ef is applied to the terminal 30 and is connected to the collector of the transistor Q11 via the phase correcting capacitor C1.

Here, during the normal operation, since the voltage Vout of the output terminal 50 is 1.0 V or more, the transistor Q2 is turned on and the transistor Q4 is turned off. For this reason,
Since the collector current of the transistor Q3 is supplied to the collector of the transistor Q5, the transistors Q6, Q7,
Q12 to Q15 turn on. As a result, the output driver circuit operates.

The video signal supplied to the input terminal 10 is amplified by the differential circuit of the transistors Q8, Q9, Q10, Q11 and then the transistor Q1 having an emitter follower configuration.
6, and output from the output terminal 50 via Q18. Here, the base voltage of the transistors Q16 and Q17 is Va
And the base-emitter drop voltage of each of the transistors Q16, Q17, Q18, Q19 is Vbe16,
Assuming that Vbe17, Vbe18, and Vbe19, the voltage Vout of the output terminal 50 can be expressed as follows.

Va + Vbe16−Vbe18 = Vout Va + Vbe17−Vbe19 = Vout For example, a sine wave is supplied to the input terminal 10 and connected to the output terminal 50 in a negative half-wave based on Vref of the sine wave output from the output terminal 50. The current flowing from the loaded load increases, and the output waveform becomes distorted. At the same time, the emitter current i19 of the transistor Q19 decreases and the emitter current i17 of the transistor Q17 increases. An increase in the current i17 results in an increase in the current i21 due to the current mirror configuration.

In the positive half-wave with reference to Vref, the emitter current of transistor Q18 increases, and the emitter current of transistor Q19 also increases. The emitter current i17 of the transistor Q17 decreases, and the emitter current i17 decreases because of the current mirror configuration.
Decrease.

If the output terminal 50 is erroneously short-circuited to the ground level, the voltage between the base and the emitter of the transistor Q2 becomes lower than the threshold value.
Turns off, and the transistor Q4 turns on. Therefore, the collector current of the transistor Q3 flows to the transistor Q4, and the transistor Q5 is turned off. For this purpose, transistors Q6, Q7, Q12-
Q15 is all turned off. As a result, no current is supplied to the output driver circuit, and the operation stops. Therefore, the transistor Q18 is turned off, and an overcurrent is prevented from flowing from the power supply Vcc to the output terminal 50 through the transistor Q18. Since the current flowing through the transistor Q4 is supplied from the constant current source transistor Q3,
This is relatively small compared to the excessive current flowing through the transistor Q18, which is not a problem.

That is, by setting the output terminal 50, which is an external terminal of the semiconductor integrated circuit, to the ground level outside the semiconductor integrated circuit, power saving of the output driver circuit can be performed. Can also be called.

The short-circuit protection circuit of the present invention can be applied not only to the output driver circuit for video signals but also to an output circuit in which a current flows when the output terminal is short-circuited to the ground level. Not done.

[0028]

As described above, the first aspect of the present invention provides
A first transistor that turns off when the level of an output terminal that is an external terminal of the semiconductor integrated circuit falls below a threshold from a ground level, and an output circuit that turns on when the first transistor turns off and outputs a signal from the output terminal. A second transistor for shutting off an operation power supply, the first transistor is turned off and the second transistor is turned on when the output terminal is at or near the ground level, so that the output circuit operates. It is possible to prevent the overcurrent from flowing from the output circuit to the output terminal due to the cutoff of the power supply, thereby protecting the output circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of a video signal output driver circuit to which a short-circuit protection circuit according to the present invention is applied.

FIG. 2 is a circuit diagram of an example of a conventional video signal output driver circuit.

[Explanation of symbols]

Reference Signs List 10 input terminal 40 short-circuit protection circuit 45 output driver circuit 50 output terminal Q1, Q3, Q6, Q8, Q9, Q14 to Q17 pn
p transistor Q2, Q4, Q5, Q7, Q10 to Q13, Q18 to Q
21 npn transistor R1 to R4 resistor C1 capacitor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02H 7/20 H03K 19/00 101F 5J032 H03K 17/08 H01L 27/04 H 5J055 17/60 27/06 101P 5J056 19/003 H03K 17/60 A H04N 5/14 F term (reference) 5C021 PA03 PA04 PA93 XA02 XA22 5F038 BH02 BH06 BH11 5F082 AA32 BC03 BC15 FA03 FA13 FA16 FA20 GA04 5G004 AA04 AB02 BA03 BA04 DA02 DA01 A01 A01 A01 A01 CA02 EA09 EB04 EC03 5J032 AA11 AB02 AC18 5J055 AX34 AX64 BX16 CX29 DX04 DX05 DX56 DX72 DX83 EX06 EX22 EY01 EY10 EY17 EZ04 FX12 FX17 FX36 GX01 5J056 AA04 BB44 BB45 CC02 DD02 DD25 DD51 FE07 FF07

Claims (1)

[Claims] A first transistor that is turned off when a level of an output terminal, which is an external terminal of the semiconductor integrated circuit, becomes lower than a threshold from a ground level; and a first transistor that is turned on when the first transistor is turned off to output from the output terminal. A short-circuit protection circuit for a semiconductor integrated circuit, comprising: a second transistor that shuts off an operation power supply of an output circuit that outputs a signal.