MIC2104YML datasheet(21/36 Pages) MICREL

21 / 36 page

Micrel, Inc.

MIC2103/04

August 2012

M9999-080712-A

MOSFET Gate Drive

The MIC2103/04 high-side drive circuit is designed to

switch an N-Channel MOSFET. Figure 1 shows a

bootstrap circuit, consisting of D1 (a Schottky diode is

recommended) and CBST. 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

SW 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 SW pin increases to

approximately VIN. Diode D1 is reverse 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 VDD supply voltage.

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

nominal high-side gate drive voltage is approximately

VDD – VDIODE, where VDIODE is the voltage drop across

D1. An approximate 30ns delay between the high-side

and low-side driver transitions is used to prevent current

from simultaneously flowing unimpeded through both

MOSFETs.

MIC2104YML 数据表(PDF) 21 Page - Micrel Semiconductor