MIC2130 Datasheet, PDF (13/20 Pages) Micrel Semiconductor – High Voltage Synchronous Buck Control IC with Low EMI Option

Micrel, Inc.
Adaptive Gate Drive
MIC2130/1
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.
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.
April 2008
13
M9999-042108-C