Semiconductor device
A semiconductor device according to related art has a problem that a clamp voltage that clamps an output voltage cannot adaptively vary in accordance with a power supply voltage, and it is thus not possible to reduce heating of a semiconductor chip to a sufficiently low level. According to one embodiment, a semiconductor device includes a drive circuit ( 10 ) that controls on and off of an output transistor ( 13 ) and an overvoltage protection circuit ( 12 ) that controls a conductive state of the output transistor ( 13 ) when an output voltage Vout reaches a clamp voltage, and the overvoltage protection circuit ( 12 ) has a circuit structure that sets the clamp voltage to vary in proportion to a power supply voltage VDD.
1. A semiconductor device comprising:
a first power supply terminal that is supplied with a first power supply;
a second power supply terminal that is supplied with second power supply;
an output voltage detection terminal to which another end of a load circuit is connected, one end of the load circuit being connected to the first power supply terminal;
a gate wire that is connected to a gate of an output transistor connected between the another end of the load circuit and the second power supply terminal;
a drive circuit that controls the output transistor; and
an overvoltage protection circuit that controls the output transistor based on a voltage difference between the second power supply terminal and the output voltage detection terminal, wherein
the overvoltage protection circuit includes
a first current source that generates a reference current having a value proportional to a voltage difference between the first power supply and the second power supply,
a second current source that generates a comparative current based on a voltage difference between the second power supply terminal and the output voltage detection terminal, and
an overvoltage protection transistor that supplies, to the gate wire, an overvoltage protection current having a value dependent on a current difference between the reference current and the comparative current.
2. The semiconductor device according to claim 1 , wherein the reference current is set to approximately twice the comparative current in a state where a voltage difference between the output voltage detection terminal and the second power supply terminal is the same as a voltage of the first power supply.
3. The semiconductor device according to claim 1 , wherein
the first current source includes
a reference current setting resistor with one end connected to the second power supply terminal,
a first transistor with a drain connected to another end of the reference current setting resistor, source connected to the first power supply terminal, and a gate and a drain connected to each other, and
a second transistor with a source connected to the first power supply terminal, a drain connected to a gate of the overvoltage protection transistor, and a gate connected in common to the gate of the first transistor,
the second current source includes
a comparative current setting resistor with one end connected to the output voltage detection terminal,
a third transistor with a drain connected to another end of the comparative current setting resistor, source connected to the second power supply terminal, and gate and a drain connected to each other, and
a fourth transistor with a source connected to the second power supply terminal, a drain connected to a gate of the overvoltage protection transistor, and a gate connected in common to the gate of the third transistor, and
the overvoltage protection transistor has a drain connected to the gate wire, and a source connected to the first power supply terminal.
4. The semiconductor device according to claim 3 , comprising:
a diode with an anode connected to the another end of the comparative current setting resistor, and a cathode connected to the drain of the third transistor.
5. The semiconductor device according to claim 1 , wherein
the first current source includes
a reference current setting resistor with one end connected to the first power supply terminal,
a first transistor with a drain connected to another end of the reference current setting resistor, source connected to the second power supply terminal, and gate and a drain connected to each other,
a second transistor with a source connected to the second power supply terminal, and a gate connected in common to the gate of the first transistor,
a third transistor with a drain connected to a drain of the second transistor, a source connected to the first power supply terminal, and a gate and a drain connected to each other, and
a fourth transistor with a source connected to the first power supply terminal, a drain connected to a gate of the overvoltage protection transistor, and a gate connected in common to the gate of the third transistor,
the second current source includes
a comparative current setting resistor with one end connected to the output voltage detection terminal,
a fifth transistor with a drain connected to another end of the comparative current setting resistor, source connected to the second power supply terminal, and gate and a drain connected to each other, and
a sixth transistor with a source connected to the second power supply terminal, a drain connected to a gate of the overvoltage protection transistor, and a gate connected in common to the gate of the fifth transistor, and
the overvoltage protection transistor has a drain connected to the gate wire, and a source connected to the first power supply terminal.
6. The semiconductor device according to claim 5 , comprising:
a diode with an anode connected to the another end the comparative current setting resistor, and a cathode connected to the drain of the fifth transistor.
7. The semiconductor device according to claim 1 , wherein
the first current source includes
a reference current setting resistor with one end connected to the first power supply terminal,
a first transistor with a drain connected to another end of the reference current setting resistor, source connected to the second power supply terminal, and gate and a drain connected to each other, and
a second transistor with a source connected to the second power supply terminal, a gate connected in common to the gate of the first transistor, and a drain connected to a gate of the overvoltage protection transistor,
the second current source includes
a comparative current setting resistor with one end connected to the output voltage detection terminal,
a third transistor with a drain connected to another end of the comparative current setting resistor, source connected to the second power supply terminal, and gate and a drain connected to each other,
a fourth transistor with a source connected to the second power supply terminal, and a gate connected in common to the gate of the third transistor, and
a fifth transistor with a source connected to the first power supply terminal, drain connected to a drain of the fourth transistor, and a gate and a drain connected to each other, and
a sixth transistor with a source connected to the first power supply terminal, a gate connected in common to the gate of the fifth transistor, and a drain connected to a gate of the overvoltage protection transistor, and
the overvoltage protection transistor has a drain connected to the gate wire, and a source connected to the first power supply terminal.
8. The semiconductor device according to claim 7 , comprising:
a diode with an anode connected to the another end of the comparative current setting resistor, and a cathode connected to the drain of the third transistor.
9. The semiconductor device according to claim 7 , comprising:
a backflow prevention diode that is connected between the drain of the overvoltage protection transistor and the gate wire.
10. The semiconductor device according to claim 1 , comprising:
a resistor that stores a current adjustment value supplied externally, wherein
the first current source makes fine adjustments of a value of the reference current based on the current adjustment value.
11. The semiconductor device according to claim 1 , comprising:
a gate discharge transistor that is connected between the gate wire and the source of the output transistor.
12. The semiconductor device according to claim 1 , wherein the output transistor is formed on the same semiconductor substrate as the overvoltage protection circuit.
13. The semiconductor device according to claim 1 , wherein the load circuit includes an inductive load.
14. A semiconductor device comprising:
a first power supply terminal that is supplied with a first power supply;
a second power supply terminal that is supplied with a second power supply;
an output voltage detection terminal to which another end of a load circuit is connected, one end of the load circuit being connected to the first power supply terminal;
a gate wire that is connected to a gate of an output transistor connected between the another end of the load circuit and the second power supply terminal;
a drive circuit that controls the output transistor; and
an overvoltage protection circuit that controls the output transistor to be conductive when a voltage difference between the second power supply terminal and the output voltage detection terminal reaches a clamp voltage that is set to be proportional to a voltage difference between the first power supply and the second power supply in a state where the output transistor is controlled to be cut off,
wherein the clamp voltage is set to a voltage when a voltage difference between the second power supply terminal and the output voltage detection terminal is approximately twice a voltage difference between the first power supply and the second power supply.