MIC4102_11 Datasheet, PDF (10/17 Pages) MIC GROUP RECTIFIERS – 100V Half Bridge MOSFET Driver with Anti-Shoot Through Protection PRELIMINARY SPECIFICATIONS

Micrel, Inc.
MIC4102
Drive
Signal
LS
Vdd
LO
External
FET
Vss
Figure 2. Low-Side Driver Block Diagram
High-Side Driver and Bootstrap Circuit
A block diagram of the high-side driver and bootstrap
circuit is shown in Figure 3. This driver is designed to
drive a floating N-channel MOSFET, whose source
terminal is referenced to the HS pin.
Vdd
HB
C_B
HO
External
FET
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 synchronous buck converter shown in Figure 4, 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 V_DD-V_D during this time (where V_D 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 V_IN. As the HS and
HB pin rise, the internal diode is reverse biased
preventing capacitor C_B from discharging.
C_VDD
Vdd
Level
shift
PWM
Q
FF
_
Q
C_B
HB
HO
HS
LO
Vin
Q1
Lout
Q2
Vout
Cout
Vss
Figure 4. High-Side Driver and Bootstrap Circuit
HS
Figure 3. High-Side Driver Block Diagram
November 2006
10
M9999-112806