MIC4600 Datasheet, PDF (11/26 Pages) Microchip Technology – 28V Half-Bridge MOSFET Driver

VDD
DL
EXTERNAL
FET
MIC4600
voltage across capacitor C_B is applied to the gate of the
upper external MOSFET. As the upper MOSFET turns
on, voltage on the SW pin rises with the source of the
high-side MOSFET until it reaches V_IN. As the SW and
BST pins rise, the diode is reverse biased preventing
capacitor C_B from discharging.
PGND
FIGURE 4-2:
Low-Side Driver Circuit.
4.2.6
HIGH-SIDE DRIVER AND
BOOTSTRAP CIRCUIT
A block diagram of the high-side driver and bootstrap
circuit is shown in Figure 4-3. This driver is designed to
drive a floating N-channel MOSFET, whose source
terminal is referenced to the SW pin. The output
voltage of the DH pin equals VDD minus the external
bootstrap diode forward voltage drop. The high-side
gate drive voltage is typically 4.5V.
A low-power, high-speed, level-shifting circuit isolates
the low side (AGND pin) referenced circuitry from the
high-side (SW pin) referenced driver. Power to the
high-side driver is supplied by the bootstrap circuit.
VDD
BST
V_IN
C_B
LEVEL
SHIFT
EXTERNAL
FET
DH
FIGURE 4-4:
MIC4600 Driving a
Synchronous Buck Converter.
4.2.7 THERMAL SHUTDOWN
Thermal shutdown protects the driver from damage
due to excessive die temperature. If the die exceeds
the high temperature threshold, the output drive is
inhibited and the FAULT pin is asserted low. The driver
automatically resumes operation, and the FAULT pin is
de-asserted, when the die temperature cools below the
lower threshold, set by the circuit’s hysteresis. If
resumed operation results in reheating of the die above
the high threshold, another shutdown cycle occurs.
The switch continues thermal cycling until the condition
has been resolved.
4.2.8 FAULT PIN
The FAULT signal is an N-channel open drain output,
which is asserted low when the MIC4600 enters
thermal shutdown.
SW
FIGURE 4-3:
High-Side Driver and
Bootstrap Circuit.
The bootstrap circuit consists of an external diode and
external capacitor, C_B. In a typical application, such as
the synchronous buck converter shown in Figure 4-4,
the SW pin is at ground potential while the low-side
MOSFET is on. During this time, the diode allows
capacitor C_B to charge up to V_DD-V_F (where V_F is the
forward voltage drop of the diode). After the low-side
MOSFET is turned off and the DH pin goes high, the
 2016 Microchip Technology Inc.
DS20005584A-page 11