A4940 データシートの表示（PDF） - Allegro MicroSystems

部品番号

コンポーネント説明

メーカー

A4940

Automotive Full Bridge MOSFET Driver

Allegro MicroSystems 

A4940

Automotive Full Bridge MOSFET Driver

FAULT Pin This is an open drain output fault flag, which indi-

cates a fault condition by its state, as shown in table 2. It must be

pulled to VDD with an external resistor, typically 10 to 47 kΩ.

Fault States

Overtemperature If the junction temperature exceeds the

over-temperature threshold, 170°C typical, the A4940 will enter

the overtemperature fault state and FAULT will go low. The

overtemperature fault state, and FAULT, will only be cleared

when the temperature drops below the recovery level defined by

TJF – TJFHYS.

No circuitry will be disabled. External control circuits must take

action to limit the power dissipation in some way so as to prevent

overtemperature damage to the A4940 chip and unpredictable

device operation.

VREG Undervoltage VREG supplies the low-side gate driver

and the bootstrap charge current. It is critical to ensure that the

voltages are sufficiently high before enabling any of the outputs.

If the voltage at VREG, VREG , drops below the falling VREG

undervoltage lockout threshold, VREGUVOFF, then the A4940

will enter the VREG undervoltage fault state. In this fault state

FAULT will be low, and the outputs will be disabled. The VREG

undervoltage fault state and the fault flags will be cleared when

VREG rises above the rising VREG undervoltage lockout thresh-

old, VREGUVON.

The VREG undervoltage monitor circuit is active during power-

up, and the A4940 remains in the VREG undervoltage fault state

until VREG is greater than the rising VREG undervoltage lockout

threshold, VREGUVON.

Bootstrap Capacitor Undervoltage The A4940 monitors the

voltage across the individual bootstrap capacitors to ensure they

have sufficient charge to supply the current pulse for the high-

side drive. Before a high-side drive can be turned on, the voltage

across the associated bootstrap capacitor must be higher than the

turn-on voltage limit. If this is not the case, then the A4940 will

start a bootstrap charge cycle by activating the complementary

low-side drive. Under normal circumstances, this will charge the

bootstrap capacitor above the turn-on voltage in a few microsec-

onds and the high-side drive will then be enabled.

The bootstrap voltage monitor remains active while the high-side

drive is active and, if the voltage drops below the turn-off volt-

age, a charge cycle will be initiated.

In either case, if there is a fault that prevents the bootstrap capaci-

tor charging, then the charge cycle will timeout, FAULT will be

low, and the outputs will be disabled. The bootstrap undervoltage

fault state remains latched until RESET is set low.

VDD Undervoltage The logic supply at VDD is monitored

to ensure correct logical operation. If the voltage at VDD, VDD,

drops below the falling VDD undervoltage lockout threshold,

VDDUVOFF , then the A4940 will enter the VDD undervoltage

fault state. In this fault state, FAULT will be low, and the outputs

will be disabled. In addition, because the state of other reported

faults cannot be guaranteed, all fault states are reset and replaced

by a VDD undervoltage fault state. For example, a VDD under-

voltage will reset an existing boostrap undervoltage fault condi-

tion and replace it with a VDD undervoltage fault. The VDD

undervoltage fault state and the fault flag will be cleared when

VDD rises above the rising VDD undervoltage lockout threshold

defined by VDDUVOFF +VDDUVHYS.

The VDD undervoltage monitor circuit is active during power-up,

and the A4940 remains in the VDD undervoltage fault state until

VDD is greater than the rising VDD undervoltage lockout thresh-

old, VDDUVOFF +VDDUVHYS.

Table 2. Fault Definitions

FAULT Pin Setting

Fault Description

Disable Outputs*

High

No Fault

No

Low

Overtemperature

No

Low

VDD undervoltage

Yes

Low

VREG undervoltage

Yes

Low

Bootstrap undervoltage

Yes

*Yes indicates all gate drives low, and all MOSFETs off.

Fault Latched

–

No

No

No

Yes

Allegro MicroSystems, Inc.

8

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Share Link: