MIC2131 datasheet(13/20 Pages) MICREL

13 / 20 page

Micrel, Inc.

MIC2130/1

April 2008

M9999-042108-C

Adaptive Gate Drive

There is a period when both driver outputs are held off

(‘dead time’) to prevent shoot through current flowing.

Shoot through current flows if both MOSFETS are on

momentarily as the same time and reduces efficiency

and can destroy the FETs. This dead time must be kept

to a minimum to reduce losses in the free wheeling

diode which could either be an external Schottky diode

placed across the lower MOSFET or the internal

Schottky diode implemented in some MOSFETs. It is not

recommended, for high current designs, to rely on the

intrinsic body diode of the power MOSFET.

These

typically have large forward voltage drops and a slow

reverse recovery characteristic which will add significant

losses to the regulator. Dependant upon the MOSFETs

used, the dead time could be required to be 150ns or

20ns. The MIC2130/31 solves this variability issue by

using an adaptive gate-drive scheme.

When the High side driver is turned off, the inductor

forces the voltage at the switching node (low side

MOSFET drain) towards ground to keep current flowing.

When the SW pin is detected to have reached 1V, the

top MOSFET can be assumed to be off and the low side

driver output is immediately turned on. There is also a

short delay between the low side drive turning off and

the high side driver turning on. This is fixed at ~80ns to

allow for large gate charge MOSFETs to be used.

MIC2131 Datasheet(PDF) 13 Page - Micrel Semiconductor