AN1625 STMicroelectronics, AN1625 Datasheet - Page 25

• Manufacturer Part Number: AN1625
• Description: L6235 THREE PHASE BRUSHLESS DC MOTOR DRIVER
• Manufacturer: STMicroelectronics

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
square-wave whose frequency is proportional to the motor rotation speed, with a fixed on-time (t
an external RC network connected at the RC
Figure 26. Tacho monostable.
Tacho monostable is identical to RCoff monostable, and the fixed pulse time is defined by:
Figure 27. tacho pulses selection.
Hall effect sensor 1
from the motor
+5V
RC
TACHO
GND
PULSE
H1
1 . 10
1 . 10
100
10
4
3
1
t
p uls e
R
Monostable
PUL
PULSE
Tacho
= 20k
0.6R
pin.
R
PULSE
PUL
Cpul [nF]
to the Decoding Logic
= 47k
10
C
PULS E
R
PUL
= 100k
AN1625 APPLICATION NOTE
100
t
PULSE
PULSE
) set by
25/39