MP8044 - 22V, 4A DUAL CHANNEL POWER HALF-BRIDGE

M8044 Rev. 1.0

www.MonolithicPower.com

7

5/5/2010

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OPERATION

The MP8044 is a high voltage, dual channel

power half-bridge driver that can be configured

as the output of a Class D amplifier. The output

is in phase with the input and the dead time is

optimized

for

symmetrical

performance,

regardless of load conditions.

When the shutdown (SHDNB) pin is low, both

channels 1 and 2 will be off. When the standby

(STBYB) is pulled low, it causes the outputs of

both channels to go into high impedance.

However, when the voltage across the BST1/2

and SW1/2 pins drops sufficiently low, the

bottom MOSFET will be turned on to refresh the

external bootstrap capacitor. For a bootstrap

capacitor of 100nF, the refresh time is

approximately 300ns.

In order to prevent erratic operation, two under

voltage lockout (UVLO) circuits are used. One

of them is to ensure that the supply for the

bottom gate drive circuit is sufficiently high and

the other is for the top gate driver.

Voltage Monitoring

The MP8044 contains a hysteretic comparator

that can easily be used for supply voltage

monitoring (see block diagram). The user can

connect a resistor from the supply that is to be

monitored to the POR_VFB pin. The trip point is

given by:

EXT

TRIP

55k + R

V

= 1.25x

55k

The hysteresis is given by:

HYS

EXT

V

= (2.27E - 6)xR

1.25V, the POR_OUT is low. The voltage swing

on the POR_VFB pin is approximately from

0.2V to 4.5V. Do not apply more than 6V to the

POR_VFB.

Fault Protection

To protect the power MOSFETs, an internal

current limit of 4A is set for all MOSFETs. When

this limit is reached, all MOSFETs will go into

high impedance for a fixed duration of

approximately 8us before resuming normal

operation.

However, in certain conditions, when the

current through the upper MOSFET exceeds 4A,

all MOSFETs will go into high impedance but

normal operation will only resume if the inductor

current has been reset to close to zero.

To enhance the robustness of the device under

short circuit condition, a capacitor can be

connected to the FaultB pin, as shown in figure

1. The time constant of the RC is selected to be

greater than 50ms for the FaultB node to reach

1V. Under short circuit condition, the FaultB

node will be reset to zero and the part will be

place in standby mode until the voltage at the

STBYB pin is above 1V.

Figure 1— Fault Protection Circuit

Fault Output

The MP8044 includes an open drain, active low

fault indicator output (FAULTB). A fault will be

indicated if the current limit is tripped or the

thermal shutdown is tripped.

A fault on any channel will cause the FAULTB

pin to be pulled low. A fault on either channel

will cause the outputs (SW1, SW2) to go into

high impedance. When the fault goes away, the

MP8044 will resume normal operation.

Do not apply more than 6V to the FAULTB pin.