MIC2159 datasheet(8/17 Pages) MICREL

8 / 17 page

Micrel

MIC2159

October 2006

M9999-101206

2.9V to 5V.

MOSFET Gate Drive

The MIC2159 high-side drive circuit is designed to

switch an N-Channel MOSFET. The Functional Block

Diagram shows a bootstrap circuit, consisting of D1 and

CBST. This circuit supplies energy to the high-side drive

circuit. Capacitor CBST circuit is charged while the low-

side MOSFET is on and the voltage on the VSW pin is

approximately 0V. When the high-side MOSFET driver is

turned on, energy from CBST is used to turn the MOSFET

on. As the MOSFET turns on, the voltage on the VSW

pin increases to approximately VIN. Diode D1 is

reversed biased and CBST floats high while continuing to

keep the high-side MOSFET on. When the low-side

switch is turned back on, CBST is recharged through D1.

The drive voltage is derived from the internal 5V VDD

bias supply. The nominal low-side gate drive voltage is

5V and the nominal high-side gate drive voltage is

approximately 4.5V due the voltage drop across D1. An

approximate 50ns delay between the low-side(off) to

high-side(on) driver transitions is used to prevent current

from simultaneously flowing unimpeded through both

MOSFETs (shoot-through). Adaptive gate drive is

implemented on the high-side(off) to low-side(on) driver

transition to reduce losses in the flywheel diode and to

prevent shoot-through. This is operated by detecting the

VSW pin; once this pin is detected to reach 1.5v, the

high-side MOSFET can be assumed to be off and the

low side driver is enabled.

MIC2159 Datasheet(PDF) 8 Page - Micrel Semiconductor