MIC4600 datasheet(11/26 Pages) MICROCHIP

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 2016 Microchip Technology Inc.

DS20005584A-page 11

MIC4600

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.

FIGURE 4-3:

High-Side Driver and

Bootstrap Circuit.

The bootstrap circuit consists of an external diode and

external capacitor, CB. 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 CB to charge up to VDD-VF (where VF is the

forward voltage drop of the diode). After the low-side

MOSFET is turned off and the DH pin goes high, the

voltage across capacitor CB 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 VIN. As the SW and

BST pins rise, the diode is reverse biased preventing

capacitor CB from discharging.

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.

PGND

VDD

EXTERNAL

FET

BST

EXTERNAL

FET

VDD

LEVEL

SHIFT

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