MIC4606 datasheet(19/40 Pages) MICROCHIP

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DS20005604D-page 19

MIC4606

6.0

FUNCTIONAL DESCRIPTION

The MIC4606 is a noninverting, 85V full-bridge

MOSFET driver designed to independently drive all

four N-channel MOSFETs in the bridge. The MIC4606

offers a wide 5.5V to 16V operating supply range with

either four independent TTL inputs (MIC4606-1) or two

PWM inputs, one for each phase (MIC4606-2). Refer to

Figure 5-1.

The drivers contain input buffers with hysteresis, three

independent UVLO circuits (two high side and one low

side) and four output drivers. The high-side output

drivers utilize a high-speed level-shifting circuit that is

referenced to its HS pin. Each phase has an internal

diode that is used by the bootstrap circuits to provide

the drive voltages for each of the two high-side outputs.

6.1

Start-up and UVLO

The UVLO circuits force the driver’s outputs low until

the supply voltage exceeds the UVLO threshold. The

low-side UVLO circuit monitors the voltage between

the VDD and VSS pins. The high-side UVLO circuits

monitor the voltage between the xHB and xHS pins.

Hysteresis in the UVLO circuits prevent noise and finite

circuit impedance from causing chatter during turn-on.

6.2

Enable Inputs

There is one external enable pin that controls both

phases. A logic high on the enable pin (EN) allows for

start-up of both phases and normal operation.

Conversely, when a logic low is applied on the enable

pin, both phases turn off and the device enters a

Low-Current Shutdown mode. All outputs (xHO and

xLO) are pulled low when EN is low. Do not leave the

EN pin floating.

6.3

Input Stage

All input pins (xLI and xHI) are referenced to the VSS pin.

The MIC4606 has a TTL-compatible input range and

can be used with input signals with amplitude less than

the supply voltage. The threshold level is independent of

the VDD supply voltage and there is no dependence

between IVDD and the input signal amplitude. This

feature makes the MIC4606 an excellent level translator

that will drive high-level gate threshold MOSFETs from a

low-voltage PWM IC.

6.4

Low-Side Driver

A block diagram of the low-side driver is shown in

Figure 6-1. It drives a ground (VSS pin) referenced

N-channel MOSFET.

Low impedances in the driver allow the external

MOSFET to be turned on and off quickly. The rail-to-rail

drive capability of the output ensures high noise immunity

and a low RDS(ON) from the external MOSFET.

A high level applied to the xLI pin causes VDD to be

applied to the gate of the external MOSFET. A low level

on the xLI pin grounds the gate of the external

MOSFET.

FIGURE 6-1:

Low-Side Driver Block

Diagram.

6.5

High-Side Driver and Bootstrap

Circuit

A block diagram of the high-side driver and bootstrap

circuit is shown in Figure 6-2. This driver is designed to

drive a floating N-channel MOSFET, whose source

terminal is referenced to the HS pin.

FIGURE 6-2:

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 (xHS pin) referenced driver. Power to the

high-side driver and UVLO circuit is supplied by the

bootstrap capacitor (CB), while the voltage level of the

xHS pin is shifted high.

EXTERNAL

FET

MIC4606

xHS

xHB

xHO

EXTERNAL

FET

MIC4606

LEVEL

SHIFT

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