3958

DMOS FULL-BRIDGE

PWM MOTOR DRIVER

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

8

APPLICATIONS INFORMATION

Current Sensing. To minimize inaccuracies in sensing

trace IR drops, the sense resistor should have an

independent ground return to the ground terminal of the

device. For low-value sense resistors the IR drops in the

PCB sense resistor’s traces can be significant and should

be taken into account. The use of sockets should be

contact resistance.

The maximum value of

Braking. The braking function is implemented by

driving the device in slow-decay mode via serial port bit

D13, enabling synchronous rectification via bit D12, and

chopping with the combination of D14 and the ENABLE

input terminal. Because it is possible to drive current in

either direction through the DMOS drivers, this

configuration effectively shorts out the motor-generated

BEMF as long as the ENABLE chop mode is asserted. It

is important to note that the internal PWM current-control

circuit will not limit the current when braking, because the

current does not flow through the sense resistor. The

ratings of the device are not exceeded in worst-case

braking situations of high speed and high inertial loads.

Thermal Protection. Circuitry turns off all drivers

when the junction temperature reaches 165

°C typically. It

is intended only to protect the device from failures due to

excessive junction temperatures and should not imply that

output short circuits are permitted. Thermal shutdown has

a hysteresis of approximately 15

°C.

Layout. The printed wiring board should use a heavy

ground plane. For optimum electrical and thermal perfor-

mance, the driver should be soldered directly onto the

board. The ground side of

path to the ground terminals of the device. This path

should be as short as is possible physically and should not

have any other components connected to it. It is recom-

mended that a 0.1

µF capacitor be placed between SENSE

and ground as close to the device as possible; the load

electrolytic capacitor (> 47

µF is recommended) placed as

close to the device as is possible.