Microstepping Driver with Translator
A3967
8
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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 24-lead SOIC has the analog ground and the
power ground internally bonded to the power tabs of the
package (leads 6, 7, 18, and 19).
Applications Information
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 indepen-
dent 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 signifi cant 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 shutdown has
a hysteresis of approximately 15°C.
