US 6,275,395 B1 · Accelerated turn-off of MOS transistors by bootstrapping

Abstract

A controller for limiting the current through a pass transistor is described herein that includes an NMOS control transistor coupled between the gate of the pass transistor and ground. The gate of the NMOS control transistor is coupled to a bootstrap circuit via a PMOS transistor. The PMOS transistor is turned on in the event of a current limit signal to momentarily apply the bootstrap voltage to the gate of the NMOS control transistor. This quickly turns on the NMOS control transistor to discharge the gate of the pass transistor, shutting off the pass transistor and terminating the high current situation. After the bootstrapped voltage has been shunted to ground, a reverse biased diode allows the gate of the NMOS control transistor to remain charged to keep the NMOS control transistor on. After the current limit situation has passed, the NMOS control transistor is switched off. Accordingly, short circuits in the load are quickly uncoupled from the remainder of the system by the fast reaction time of the NMOS control transistor.

Claims19

Dependent claims

A circuit comprising:

a first terminal for receiving a supply voltage;
an NMOS pass transistor having a gate, said pass transistor coupled between said first terminal and a second terminal;
a charge pump coupled to said gate of said pass transistor for providing an enhanced voltage, derived from said supply voltage, greater than said supply voltage;
an NMOS control transistor coupled to said gate of said pass transistor for discharging the gate of said pass transistor when said NMOS control transistor is turned on;
a PMOS transistor coupled to receive said enhanced voltage and being coupled to said gate of said NMOS control transistor, said PMOS transistor having a gate;
a current detector providing a current threshold signal;
and
a controller coupled to said gate of said PMOS transistor and to a gate of said NMOS control transistor, said controller turning on said PMOS transistor to charge said gate of said NMOS transistor to approximately said enhanced voltage to turn on said NMOS control transistor in response to said current threshold signal.

5 more elements

Dependencies are inferred from the claim text.

Accelerated turn-off of MOS transistors by bootstrapping

Life of this patent

Accelerated turn-off of MOS transistors by bootstrapping

Life of this patent

Abstract

Claims19