MIC4103 Datasheet, PDF (10/17 Pages) Micrel Semiconductor – 100V Half Bridge MOSFET Drivers 3/2A Sinking/Sourcing Current

Micrel
Figure 2. MIC4103 Supply Current vs. Input Voltage
MIC4103/4104
The MIC4104 has a TTL compatible input range and is
recommended for use with inputs signals whose amplitude
is less than the supply voltage. The threshold level is
independent of the VDD supply voltage and there is no
dependence between I_VDD and the input signal amplitude
with the MIC4104. This feature makes the MIC4104 an
excellent level translator that will drive high threshold
MOSFETs from a low voltage PWM IC.
Low-Side Driver
A block diagram of the low-side driver is shown in Figure
3. The low-side driver is designed to drive a ground (V_SS
pin) referenced N-channel MOSFET. Low driver
impedances allow the external MOSFET to be turned on
and off quickly. The rail-to-rail drive capability of the output
ensures full enhancement of the external MOSFET.
A high level applied to LI pin causes the upper driver FET
to turn on and V_DD voltage is applied to the gate of the
external MOSFET. A low level on the LI pin turns off the
upper driver and turns on the low side driver to ground the
gate of the external MOSFET.
Vdd
External
FET
LO
Vss
Figure 3. 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 4. This driver is designed to drive
a floating N-channel MOSFET, whose source terminal is
referenced to the HS pin.
Figure 4. High-Side Driver and Bootstrap Circuit Block
Diagram
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 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
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
HI
Vdd
Level
shift
C_B
HB
HO
Vin
Q1
Lout
HS
Q2
LI
LO
Vss
October 2007
Figure 5. High-Side Driver and Bootstrap Circuit
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M9999-100107-B