3977 データシートの表示（PDF） - Allegro MicroSystems

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3977

MICROSTEPPING DMOS DRIVER WITH TRANSLATOR

Allegro MicroSystems 

3977

MICROSTEPPING DMOS DRIVER

WITH TRANSLATOR

Applications Information

Layout.

The printed wiring board should use a heavy ground

plane.

For optimum electrical and thermal performance, the

driver should be soldered directly onto the board.

The load supply terminal, VBB, should be decoupled

with an electrolytic capacitor (>47 µF is recommended)

placed as close to the device as possible.

To avoid problems due to capacitive coupling of the

high dv/dt switching transients, route the bridge-output

traces away from the sensitive logic-input traces. Always

drive the logic inputs with a low source impedance to

increase noise immunity.

Grounding. A star ground system located close to the

driver is recommended.

The 44-lead PLCC has the analog ground and the

power ground internally bonded to the power tabs of the

package (leads 44, 1, 2, 11 – 13, 22 – 24, and 33 – 35).

On the 28-lead TSSOP package, the analog ground

(lead 7) and the power ground (lead 21) must be con-

nected together externally. The copper ground plane

located under the exposed thermal pad is typically used as

the star ground.

Current Sensing. To minimize inaccuracies caused by

ground-trace IR drops in sensing the output current level,

the current-sense resistor (RS) should have an independent

ground return to the star ground of the device. This path

should be as short as possible. For low-value sense

resistors the IR drops in the printed wiring board sense

resistor’s traces can be significant and should be taken

into account. The use of sockets should be avoided as

they can introduce variation in RS due to their contact

resistance.

Allegro MicroSystems recommends a value of RS

given by

RS = 0.5/ITRIPmax

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 shut-

down has a hysteresis of approximately 15°C.

www.allegromicro.com

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