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AN1625 APPLICATION NOTE

2.15 Tacho Output and Speed Loop

H1 input is internally connected to a monostable that provides, through an open drain mosfet, a fixed width pulse

on the tacho output (see Figure 26). Through this output realizing a speed loop is very easy and inexpensive.

Providing an external pull-up resistor on this open drain output, the resulting waveform at the pin will be a

Figure 26. Tacho monostable.

Tacho monostable is identical to RCoff monostable, and the fixed pulse time is defined by:

Figure 27. tacho pulses selection.

H1

TACHO

Tacho

Monostable

to the Decoding Logic

+5V

GND

Hall effect sensor 1

from the motor

t

puls e

0.6R

≅

1

10

100

10

100

1 .10

3

1 .10

4

Cpul [nF]