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, V
BB
, 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 (R
S
) 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 R
S
due to their contact
resistance.
Allegro MicroSystems recommends a value of R
S
given by
R
S
= 0.5/I
TRIP
max
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.
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9
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