MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA

34923

13

APPLICATIONS

Current Sensing

which may be caused by ground trace IR drops, the sense

resistor should have an independent ground return to the

ground pin 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

their contact resistance.

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 PWM/ENABLE input pin. Because it is possible to

drive current in either direction through the drivers, this

configuration effectively shorts out the motor-generated back

EMF (BEMF) as long as the PWM/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

Care should be taken to ensure that the maximum 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 owing 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 performance (see following

Note), the driver should be soldered directly onto the board. The

pins 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 recommended that a 0.1

µF capacitor be

placed between SENSE and ground as close to the device as

electrolytic capacitor (>47

µF is recommended) placed as close

to the device as is possible.

Note The thermal resistance and absolute maximum

allowable package power dissipation specified in the

MAXIMUM RATINGS table, page 4, is measured on typical

two-sided PCB with minimal copper ground area. For the

ground area, as shown in Figure 3.

Figure 3. Package Dissipation Temperature Derating

TEMPERATURE (°C)

50

100

150

125

5

4

3

2

1

0

75

25

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com