MIC2124YMM datasheet(11/24 Pages) MICREL

11 / 24 page

Micrel, Inc.

MIC2124

June 2010

M9999-060810-D

MOSFET Gate Drive

The MIC2124 high-side drive circuit is designed to

switch an N-Channel MOSFET. The typical application

circuit shows a bootstrap circuit, consisting of a Schottky

diode D1 and 0.1μF boostrap capacitor CBST, as shown

in the typical application schematic on Page 1. This

circuit supplies energy to the high-side drive circuit.

Capacitor CBST is charged while the low-side MOSFET is

on and the voltage on the LX 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 high-

side MOSFET turns on, the voltage on the LX pin

increases to approximately VHSD. Diode D1 is reversed

biased and CBST floats high while continuing to keep the

high-side MOSFET on. The bias current of the high-side

driver is less than 10mA so a 0.1μF to 1μF is sufficient to

hold the gate voltage with minimal droop for the power

stroke (high-side switching) cycle, i.e., ΔBST = 10mA x

3.33μs/0.1μF = 333mV. When the low-side MOSFET is

turned back on, CBST is recharged through D1. A small

resistor RG, which is in series with CBST, can be used to

slow down the turn-on time of the high-side N-Channel

MOSFET.

The drive voltage is derived from the supply voltage VIN.

The nominal low-side gate drive voltage is VIN and the

nominal high-side gate drive voltage is approximately

VIN - VDIODE, where VDIODE is the voltage drop across D1.

A dead-time of approximate 30ns between the high-side

and low-side driver transitions is used to prevent current

from simultaneously flowing unimpeded through both

MOSFETs.

MIC2124YMM Datasheet(PDF) 11 Page - Micrel Semiconductor