TDA7272A View Datasheet(PDF) - STMicroelectronics
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TDA7272A Datasheet PDF : 16 Pages
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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-
Figure 2: Application Circuit.
TDA7272A
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.
5/16
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