TMC249 / TMC249A DATA SHEET (V2.09 / 2009-Jul-30)
19
Unipolar Operation
The TMC249 can also be used in a unipolar motor application with microstepping. In this configuration,
only the four upper power transistors are required.
Differences of short circuit behavior in unipolar operation mode
Since there is no possibility to disable a short to VS condition, the circuit is not completely short circuit
proof. In a low cost application a motor short would be covered, just using the bottom sense resistors
(see schematic).
Differences in chopper cycle in unipolar operation mode
In unipolar mode, one of the upper side transistors is chopped, depending on the phase polarity. Slow
decay mode always means, that both transistors are disabled. There is no difference between slow
and fast decay mode, and the mixed decay control bits are “don’t care”. The transistors have to stand
an off voltage, which is slightly higher than the double of the supply voltage. Voltage decay in the coil
can be adapted to the application by adding additional diodes and a zener diode to feed back coil
current in flyback conditions to the supply.
+VM
HA1
HA2
P
P
TMC249/
TMC239
One coil of
the motor
LA2
LA1
RS
SRA
Copyright © 2005, TRINAMIC Motion Control GmbH & Co KG
TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
