Driving circuit for high-side transistor
A driving circuit drives an N-channel or NPN high-side transistor. A level shift circuit includes an open-drain differential conversion circuit that converts an input signal S IN into a differential signal S diffP /S diffN , and a latch circuit that switches its state according to the differential output S diffP /S diffN of the differential conversion circuit. A driver drives a high-side transistor according to an output of the level shift circuit. A bootstrap circuit generates a bootstrap voltage V BST to be used as an upper-side power supply for the driver. Upon detecting an abnormal state, a protection circuit controls at least a part of the driving circuit except for the input signal S IN so as to turn off the high-side transistor.
1. A driving circuit for an N-channel or otherwise NPN high-side transistor, the driving circuit comprising:
a level shift circuit comprising an open-drain differential conversion circuit structured to convert an input signal into a differential signal, and a latch circuit structured to transit according to a differential output of the differential conversion circuit;
a driver structured to drive the high-side transistor according to an output of the level shift circuit;
a bootstrap circuit structured to generate a bootstrap voltage to be used as an upper-side power supply for the driver; and
a protection circuit structured to cause turn off of the high-side transistor in an abnormal state,
wherein the protection circuit is structured to lower the bootstrap voltage in the abnormal state, and wherein the protection circuit comprises a discharge transistor arranged between a bootstrap line at which the bootstrap voltage is generated and a ground line,
wherein the protection circuit is structured to turn on the discharge transistor in the abnormal state.
2. The driving circuit according to claim 1 , wherein the protection circuit is structured to discharge a bootstrap capacitor of the bootstrap circuit in the abnormal state.
3. The driving circuit according to claim 1 , wherein the protection circuit is structured to pull down a voltage of a control terminal of the high-side transistor in the abnormal state.
4. The driving circuit according to claim 1 , wherein, when a power supply voltage for the differential conversion circuit becomes lower than a predetermined threshold value, the protection circuit judges that the abnormal state has occurred.
5. The driving circuit according to claim 4 , wherein the protection circuit is structured to employ, as a power supply thereof, a separate DC voltage system that differs from that of the power supply voltage.
6. A driving circuit for an N-channel or otherwise NPN high-side transistor, the driving circuit comprising:
a level shift circuit comprising an open-drain differential conversion circuit structured to convert an input signal into a differential signal, and a latch circuit structured to transit according to a differential output of the differential conversion circuit;
a driver structured to drive the high-side transistor according to an output of the level shift circuit;
a bootstrap circuit structured to generate a bootstrap voltage to be used as an upper-side power supply for the driver; and
a protection circuit structured to cause turn off of the high-side transistor in an abnormal state,
wherein, when a power supply voltage for the differential conversion circuit becomes lower than a predetermined threshold value, the protection circuit judges that the abnormal state has occurred,
and wherein the protection circuit is structured to employ, as a power supply thereof, a separate DC voltage system that differs from that of the power supply voltage,
wherein the protection circuit comprises:
a second transistor having one end being grounded, and an other end to which DC voltage is supplied to via a resistor; and
a voltage dividing circuit structured to divide the power supply voltage, and to supply the divided voltage to a control terminal of the second transistor,
wherein an on/off state of the second transistor indicates a detection result of the abnormal state.
7. The driving circuit according to claim 6 , wherein the DC voltage is configured as the bootstrap voltage.
8. The driving circuit according to claim 6 , wherein the DC voltage is configured as an input voltage to be supplied to a drain of the high-side transistor.
9. The driving circuit according to claim 6 , wherein the DC voltage is configured as a voltage to be supplied to the bootstrap circuit.
10. A control circuit for a DC/DC converter, comprising:
a pulse generator structured to generate a pulse signal such that the DC/DC converter or otherwise a load thereof approaches a desired state; and
the driving circuit according to claim 1 , structured to receive an output of the pulse generator as an input thereof, and to drive a high-side transistor.
11. The control circuit according to claim 10 , monolithically integrated on a single semiconductor substrate.
12. A DC/DC converter comprising the control circuit according to claim 10 .