TDA7272A datasheet(5/16 Pages) STMICROELECTRONICS

5 / 16 page

BLOCK DESCRIPTION

The principle structure of the element is shown in

fig. 2. As to be seen, the motor speed information

is derived from the motor current sense drop

across the resistors RS ; capacitor CD together

with the input impedance of 500

Ω at pin 1 real-

izes a high pass filter.

This pin is internally biased at 20 mV, each nega-

tive zero transition switches the input comparator.

A 10 mV hysteresis improves the noise immunity.

The trigger circuit is followed by an internal delay

time differentiator.

Thus, the system becomes widely independent of

the applied waveform at pin 1, the differentiator

triggers a monostable circuit which provides a

constant current duration. Both, output current

magnitude and duration T, are adjustable by ex-

ternal elements CT and RT.

The monostable is retriggerable ; this function

prevents the system from fault stabilization at

higher harmonics of the nominal frequency.

The speed programming current is generated by

two separate external adjustable current sources.

A corresponding digital input signal enables each

current source for left or right rotation direction.

Resistor RP1 and RP2 define the speed, the logi-

cal inputs are at pin 18 and 19.

At the inverting input (pin 14) of the main amplifier

the reference current is compared with the pulsed

monostable output current.

For the correct motor speed, the reference cur-

rent matches the mean value of the pulsed

monostable current. In this condition the charge

of the feedback capacitor becomes constant.

Figure 2: Application Circuit.

TDA7272A

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TDA7272A Datasheet(PDF) 5 Page - STMicroelectronics