2961
HIGH-CURRENT
HALF-BRIDGE
PRINTHEAD/MOTOR DRIVER
The load supply (VBB) should be well decoupled with a capacitor
placed as close as possible to the device.
The EMITTER pin should be connected to a high-current power
ground.
Thermal shutdown protection circuitry is activated and turns OFF
both output drivers at a junction temperature of typically +165°C. It is
intended only to protect the device from catastrophic failures due to
excessive junction temperatures and should not imply that output short
circuits are permitted. The output drivers are re-enabled when the
junction temperature cools down to approximately +145°C.
MOTOR DRIVER APPLICATIONS
Two UDN2961B/Ws can be cross connected as shown to form a
full-bridge driver circuit. Two full-bridge circuits are needed to drive a
two-phase bipolar stepper motor. When in a full-bridge configuration,
one INPUT signal must be logically inverted from the other INPUT
signal to prevent the simultaneous conduction of a source driver from
one half-bridge and the sink driver from the other half-bridge. In order
to prevent crossover currents, a turn-ON delay time of 3 µs is needed
between the time an INPUT signal for one of the half bridges goes high
and the INPUT signal for the other half bridge goes low.
In addition to the two external ground clamp diodes, diodes in
series with the load to the SINK OUT are needed in a full-bridge
configuration. These series diodes prevent the sink drivers from
conducting on the inverse mode, which can occur when the opposite
half-bridge ground clamp diode is conducting and forces the sink driver
collector below ground.
If fast current decay is used (MODE = logic high) or pulse width
modulation of the load-current direction is used, diodes in series with
the load to the SOURCE OUT are needed. These series diodes
prevent the SOURCE OUT from inverse conducting during the recircu-
lation period and thereby prevent shoot-through currents from occuring
as the drivers turn back ON.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
ALLEGRO [ ALLEGRO MICROSYSTEMS ]
