E-TEA3718DP datasheet(18/26 Pages) STMICROELECTRONICS

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Functional description

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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, toff, which is determined by the

timing components RT and CT. toff = 0.69 ⋅ RT CT

The single pulse switches off the power feed to the motor winding, causing the winding

current to decrease during toff. If a new trigger signal should occur during toff, it is ignored.

5.5

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.

Note:

It is not permitted to short circuit the outputs.

5.6

SS, VS and VR

The circuit stands any order of turn-on or turn-off the supply voltages VSS and VS. Normal

dV/dt values are then assumed.

Preferably, VR should track VSS during power on and power off if VS 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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