Integrated reverse battery protection circuit for an external MOSFET switch
A reverse battery protection circuits that provides an integrated reverse battery condition solution for protection of external NMOS switches during the reverse battery condition is disclosed herein. This reverse battery protection circuit minimizes power consumption during a reverse battery event wherein there is no need for mechanical adjustments such as heat sinking and clamping to extract the heat away from the silicon and not destroy the device. Specifically, the reverse battery protection circuit includes a push-pull gate drive circuit coupled between the first and second power supply rail. A protection subcircuit portion connects between a first output node and the second power supply rail to turn the external FET ‘on’ during the reverse battery condition. In particular, the protection subcircuit portion connects to the external FET device and includes a p-channel device connected between a second output node that biases the external FET device and a first diode. A resistor connects between a first output node of the reverse battery protection circuit to provide a voltage drop between the drain terminal and the gate of the p-channel device. A second diode connects between the gate and the source of the p-channel device. In addition, a clamping circuit connects between the second output node and the third output node to provide clamping in the instance where the voltage at the second output node momentarily rises too high.
1. A reverse battery protection circuit coupled between a first and second power supply rail, the reverse battery protection circuit having a first, a second and a third output node, wherein an external switching device couples between the first output node and the third output node and wherein the external switching device is biased by the second output node, and wherein a load couples between the third output node and the second power supply rail comprising:
a push-pull gate drive circuit coupled between the first and second power supply rail;
a protection subcircuit portion coupled between the first output node and the second power supply rail, the protection subcircuit portion comprises,
a first resistor coupled between the first output node and a first node,
a first diode coupled between the first node and a second node,
a first p-channel device coupled between the second output node and
the second node, wherein first p-channel device is biased by the first node,
a second diode coupled between the second node and ground; and
a clamping circuit coupled between the second output node and the third output node.
2. The reverse battery protection circuit as recited in claim 1 , wherein the push-pull gate drive circuit comprises:
a second p-channel device coupled between the power supply rail and a third node;
a third diode coupled between the third node and the second output node;
a fourth diode coupled between the second output node and a fourth node; and
a n-channel device coupled between the fourth node and grounds.
3. The reverse battery protection circuit as recited in claim 1 , wherein the clamping circuit comprises,
a third diode coupled to the second output node;
a fourth diode coupled in series between the third diode and the third output node; and
a second resistor coupled in parallel across the series connected third and fourth diodes.
4. The reverse battery protection circuit as recited in claim 1 , the first diode is a Zener diode.
5. The reverse battery protection circuit as recited in claim 1 , the second diode, is a Schottky diode.
6. The reverse battery protection circuit as recited in claim 1 , wherein the first p-channel device is a P-type transistor.
7. The reverse battery protection circuit as recited in claim 6 , wherein the first P-type transistor is a metal oxide semiconductor field-effect transistor.
8. The reverse battery protection circuit as recited in claim 2 , the third and fourth diodes are Schottky diodes.
9. The reverse battery protection circuit as recited in claim 2 , wherein the second p-channel device is a P-type transistor.
10. The reverse battery protection circuit as recited in claim 9 , wherein the second P-type transistor is a metal oxide semiconductor field-effect transistor.
11. The reverse battery protection circuit as recited in claim 2 , wherein the n-channel device is a N-type transistor.
12. The reverse battery protection circuit as recited in claim 11 , wherein the N-type transistor is a metal oxide semiconductor field-effect transistor.
13. The reverse battery protection circuit as recited in claim 3 , the third and fourth diodes are Zener diodes.