L6235Q datasheet(17/33 Pages) STMICROELECTRONICS

Part #	L6235Q

Description	Tacho output for speed loop

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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17 / 33 page

L6235Q

Circuit description

Doc ID 018997 Rev 2

17/33

where CPUL should be chosen in the range 1 nF … 100 nF and RPUL in the range 20 kΩ …

100 k

Ω.

By connecting the tachometer pin to an external pull-up resistor, the output signal average

value VM is proportional to the frequency of the Hall effect signal and, therefore, to the

motor speed. This realizes a simple frequency-to-voltage converter. An op amp, configured

as an integrator, filters the signal and compares it with a reference voltage VREF, which sets

the speed of the motor.

Figure 16.

Tacho operation waveforms

Figure 17.

Tachometer speed control loop

PULSE

------------------ V

⋅

t PULSE

VTACHO

VDD

CREF2

RPUL

CPUL

RDD

CREF1

VREF

TACHO

MONOSTABLE

RCPULSE

VDD

VREF

L6235Q Datasheet(PDF) 17 Page - STMicroelectronics