TDA7272A datasheet(7/16 Pages) STMICROELECTRONICS

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Pin 2

Timing resistor. An internal reference voltage

(V2 = 0.8 V) gives possibility to fix by an external

resistor (RT), from this pin and ground, the output

current amplitude of the monostable circuit, which

will be reflected into the timing capacitor (pin 3) ;

the typical value would be about 50

µ A.

Pin 3

Timing capacitor. A constant current, determined

by the pin 2 resistor, flowing into a capacitor be-

tween pin 3 and ground provides the output pulse

width of the monostable circuit, the max voltage

at pin 3 is fixed by an internal threshold : after

reaching this value the capacitor is rapidly dis-

charged and the pulse width is fixed to the value :

Ton = 2.88 RT CT (fig. 6)

Pin 4

Not connected.

Pin 5

Ground. Connected with pins 6, 15, 16.

Pin 6

Ground. Connected with pins 5, 15, 16.

Pin 7

Not connected.

Pin 8

Input V/I loop. Receives from pin 10, through a

low pass filter, the voltage with the information of

the current flowing into the motor and produces a

negative resistance output :

Rout =

− 9RS (fig. 7)

For compensating the motor resistance and

avoiding instability :

≤

RMOTOR

The optimization of the resistor RS for the tacho-

metric control must not give a voltage too high for

the V/I stage : one solution can be to divide in two

parts, as shown in fig. 8, with :

RS2 =

and RS1 + RS2 ≥

30mV

∆ I mot min.

(see pin 1 sect.)

The low pass filter RL,CL must be calculated in

order to reduce the ripple of the motor commuta-

tion at least 20 dB. Another example of possible

pins 10-8 connections is showed on fig. 9. A

choke can be used in order to reduce the radia-

tion.

Figure 5.

Figure 6.

Figure 7.

TDA7272A

7/16

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