MP8048 - 22V, 4A QUAD CHANNEL POWER HALF-BRIDGE

M8048 Rev. 1.1

www.MonolithicPower.com

8

9/10/2009

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OPERATION

The MP8048 is a quad 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 (SHDN) pin is low, all

channels will be off. When the standby (STBYB)

is pulled low, it causes the outputs of all

channels to go into high impedance. However,

when the voltage across the BST1A/1B/2A/2B

and SW1A/1B/2A/2B 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.

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.

Thermal monitoring is also integrated into the

MP8048. If the die temperature rises above

150ºC, all switches are turned off. The

temperature must fall below 130ºC before

normal operation resumes.

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 Enhancement

Circuit

Fault Output

The MP8048 includes an open drain, active low

fault indicator output (FAULTB). A fault will be

indicated if one of the following conditions is

detected: 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 (SW1A, SW1B, SW2A,

SW2B) to go into high impedance. When the

fault goes away, the MP8048 will resume

normal operation.

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