A4940 查看數據表（PDF） - Allegro MicroSystems

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A4940

Automotive Full Bridge MOSFET Driver

Allegro MicroSystems 

A4940

Automotive Full Bridge MOSFET Driver

on the upper half of the drive, sourcing current to the gate of the

high-side MOSFET in the external motor-driving bridge, turning

it on. GHx going low turns on the lower half of the drive, sinking

current from the external MOSFET gate circuit to the correspond-

ing Sx pin, turning off the MOSFET.

CA and CB Pins These are the high-side connections for the

bootstrap capacitors and are the positive supply for the high-side

gate drives. The bootstrap capacitors are charged to approxi-

mately VREG when the associated output Sx terminal is low.

When the Sx output swings high, the charge on the bootstrap

capacitor causes the voltage at the corresponding Cx terminal to

rise with the output to provide the boosted gate voltage needed

for the high-side MOSFETs.

RDEAD Pin This pin controls internal generation of dead time

during MOSFET switching. Cross-conduction is prevented

by the gate drive circuits, which introduce a dead time, tDEAD,

between switching one MOSFET off and the complementary

MOSFET on.

• When an external resistor greater than 3 kΩ is connected be-

tween RDEAD and AGND, the dead time is derived from the

resistor value.

• When RDEAD is connected directly to VDD, tDEAD defaults to

a value of 6 μs typical.

Logic Control Inputs

Four low voltage-level digital inputs provide control for the gate

drives. These logic inputs all have a typical hysteresis of 500 mV

to improve noise performance. They provide individual direct

control over each power MOSFET, subject to cross-conduction

prevention, and can be used together to provide fast decay or

slow decay with high-side or low-side recirculation.

AHI, ALO, BHI and BLO Pins These directly control the gate

drives. The xHI inputs control the high-side drives and the xLO

inputs control the low-side drives. Internal lockout logic ensures

that the high-side output drive and low-side output drive cannot

be active simultaneously. Table 1 shows the logic truth table.

RESET Pin This is an active-low input, and when active it

allows the A4940 to enter sleep mode. When RESET is held low,

the regulator and all internal circuitry are disabled and the A4940

enters sleep mode. Before fully entering sleep mode, there is a

short delay while the regulator decoupling and storage capacitors

discharge. This typically takes a few milliseconds, depending on

the application conditions and component values.

During sleep mode, current consumption from the VBB supply

is reduced to a minimal level. In addition, latched faults and the

corresponding fault flags are cleared. When the A4940 is coming

out of sleep mode, the protection logic ensures that the gate drive

outputs are off until the charge pump reaches its correct operat-

ing condition. The charge pump stabilizes in approximately 3 ms

under nominal conditions.

RESET can be used also to clear latched fault flags without enter-

ing sleep mode. To do so, hold RESET low for the reset pulse

time, tRES . This clears the latched bootstrap capacitor undervolt-

age fault that disables the outputs.

Note that the A4940 can be configured to start without any exter-

nal logic input. To do so, pull up the RESET pin to VBB by means

of an external resistor. The resistor value should be between

20 and 33 kΩ.

Diagnostics

Several diagnostic features are integrated into the A4940 to

provide indication of fault conditions. In addition to system wide

faults such as undervoltage and overtemperature, the A4940 inte-

grates individual bootstrap voltage monitors for each bootstrap

capacitor.

Table 1. Input Logic

Pin Setting

RESET xHI

xLO

GHx

GLx

H

H

L

H

L

H

L

H

L

H

H

H

H

L

H

H

L

L

L

L

L

x

x

Z

Z

Mode of Operation

Sx

H High side MOSFET conducting

L Low Side MOSFET conducting

L Low Side MOSFET conducting – cross-conduction prevention

Z High side and low side off

Z All gate drives inactive, all MOSFETs off

Allegro MicroSystems, Inc.

7

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

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