E-TEA3718DP Datasheet, PDF (18/26 Pages) STMicroelectronics – Stepper motor driver

Functional description
5.4
Single-pulse generator
The pulse generator is a monostable triggered on the positive going edge of the comparator
output. The monostable output is high during the pulse time, t_off, which is determined by the
timing components R_T and C_T. toff = 0.69 ⋅ R_T C_T
The single pulse switches off the power feed to the motor winding, causing the winding
current to decrease during t_off. If a new trigger signal should occur during t_off, it is ignored.
5.5
Note:
Output stage
The output stage contains four Darlington transistors and four diodes, connected in an H-
bridge. The two sinking transistors are used to switch the power supplied to the motor
winding, thus driving a constant current through the winding.
It is not permitted to short circuit the outputs.
5.6
V_SS, V_S and V_R
The circuit stands any order of turn-on or turn-off the supply voltages V_SS and V_S. Normal
dV/dt values are then assumed.
Preferably, V_R should track V_SS during power on and power off if V_S is established.
5.7
Analog control
The current levels can be varied continuously if VR is varied with a circuit varying the voltage
on the comparator terminal.
Figure 21. Power losses against output current
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