MIC4100 Datasheet, PDF (11/18 Pages) Micrel Semiconductor – 100V Half Bridge MOSFET Drivers

Micrel, Inc.
Vdd
LO
External
FET
MIC4100/1
synchronous buck converter shown in Figure 5, the HS pin
is at ground potential while the low-side MOSFET is on.
The internal diode allows capacitor C_B to charge up to
Vdd-Vd during this time (where Vd is the forward voltage
drop of the internal diode). After the low-side MOSFET is
turned off and the HO pin turns on, the voltage across
capacitor C_B is applied to the gate of the upper external
MOSFET. As the upper MOSFET turns on, voltage on the
HS pin rises with the source of the high-side MOSFET until
it reaches Vin. As the HS and HB pin rise, the internal
diode is reverse biased preventing capacitor C_B from
discharging.
Vss
Figure 3
C_VDD
HI
Vdd
Level
shift
LI
C_B
HB
HO
HS
LO
Vin
Q1
Lout
Q2
Vout
Cout
High-Side Driver and Bootstrap Circuit
A block diagram of the high-side driver and bootstrap
circuit is shown in Figure 4. This driver is designed to drive
a floating N-channel MOSFET, whose source terminal is
referenced to the HS pin.
Vss
Figure 5
Vdd
HB
C_B
HO
External
FET
HS
Figure 4
A low power, high speed, level shifting circuit isolates the
low side (VSS pin) referenced circuitry from the high-side
(HS pin) referenced driver. Power to the high-side driver
and UVLO circuit is supplied by the bootstrap circuit while
the voltage level of the HS pin is shifted high.
The bootstrap circuit consists of an internal diode and
external capacitor, C_B. In a typical application, such as the
March 2006
11
M9999-031506