L6235 STMicroelectronics, L6235 Datasheet - Page 14

• Manufacturer Part Number: L6235
• Description: DMOS DRIVER FOR THREE-PHASE BRUSHLESS DC MOTOR
• Manufacturer: STMicroelectronics

L6235
TACHO
A tachometer function consists of a monostable, with constant off time (t
signal (H
14. For component values refer to Application Information section.
The monostable output drives an open drain output pin (TACHO). At each rising edge of the Hall Effect Sensors
H
t
to the pin RCPULSE. Figure 16 gives the relation between t
where C
By connecting the tachometer pin to an external pull-up resistor, the output signal average value V
tional to the frequency of the Hall Effect signal and, therefore, to the motor speed. This realizes a simple Fre-
quency-to-Voltage Converter. An op amp, configured as an integrator, filters the signal and compares it with a
reference voltage V
Figure 14. Tacho Operation Waveforms.
14/25
PULSE
1
, the monostable is triggered and the MOSFET connected to pin TACHO is turned off for a constant time
t
PULSE
V
(see Figure 15). The off time t
M
PUL
1
). It allows developing an easy speed control loop by using an external op amp, as shown in Figure
=
should be chosen in the range 1nF … 100nF and R
= 0.6 · R
t
----------------- - V
P ULS E
T
REF
PUL
, which sets the speed of the motor.
DD
· C
V
PUL
TACHO
H
H
H
V
M
1
2
3
PULSE
can be set using the external RC network (R
t
PULSE
V
T
DD
PULSE
PUL
and C
in the range 20K
PULSE
PUL
, R
), whose input is one Hall Effect
PUL
. We have approximately:
… 100K .
PUL
, C
PUL
) connected
M
is propor-