8925

3-PHASE BRUSHLESS DC MOTOR CONTROLLER/DRIVER

WITH LINEAR CURRENT CONTROL

AND POWER DMOS OUTPUTS

developed that is gated in by the sequential

control logic to drive the gate of the appropri-

ate output sink transistor. A

transconductance control function is thus re-

pensation components used to obtain optimal

response and settling of the current control

loop. Information on how to select these

components is available.

FAULT. The FAULT terminal when low

indicates the presence of one of three fault

conditions:

A)

An under-voltage condition

on the logic supply. The

trip point for this function is

between 8 and 9.5 volts.

B)

An invalid Hall input combi-

nation … all inputs High or

all inputs Low.

C)

An excessive device

junction temperature. The

thermal shutdown circuitry

disables the output drivers

in addition to forcing the

FAULT output signal low.

TACH and POLE. In order to develop a

controlling motor speed, the A8925CEB di-

number of poles in the motor. This elimi-

nates the jitter caused by variations in Hall-

effect device placement , sensitivity, and

magnet strengths by always changing state

when looking at the same magnet/sensor

every mechanical revolution of the motor.

pole motors when Low or eight-pole motors

when High.

with open-collector Hall-effect devices. Internal 25 k

Ω pull up resistors

to 10 volts are connected to these inputs.

ENABLE. The ENABLE terminal when Low puts the device in a

low current consumption, power-down mode. When ENABLE is High

the device is active.

BRAKE. When the BRAKE input goes Low the output source driv-

ers are disabled and the gates of the sink drivers are pulled high and

left floating. This achieves optimum passive braking performance

since the sink power DMOS output drivers are ON until the motor has

fully completed braking. The braking control circuitry operates off the

using the back-EMF voltage of the motor as it’s supply.

tion for the power output drivers and braking control circuitry. This ter-

minal should be decoupled with a large-value capacitor to absorb load

currents dumped back into the supply during the de-energization of

motor windings. These currents can cause the supply voltage to ex-

ceed the maximum voltage rating of the device if not properly

decoupled. The intrinsic ground clamp and flyback diodes will rectify

the motor’s back-EMF voltage during power loss. In applications were

use of the motor’s back-EMF voltage is desired a series diode should

avoid dumping the charge back into the supply and therefor clamping

the voltage available from rectification of the motor’s back-EMF

voltage.

A8925CEB and powers all circuitry except the power outputs and

brake control circuitry.

LOGIC GROUND. This must be connected to the power ground

terminals in systems that do not use separate power and logic

grounds.

POWER GROUND. Terminals 7 through 17 and 29 through 39

are webbed together and attach to the die mounting area to form a low

thermal resistance path to allow heat to be conducted out of the de-

vice. The power dissipation of the package can be further enhanced

by soldering these terminals to a large area of copper foil on the

printed wiring board.