TDA7272A datasheet(8/16 Pages) STMICROELECTRONICS

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Pin 9

Output motor left. The four power transistors are

realized as darlington structures. The arrange-

ment is controlled by the logic status at pins 18

and 19.

As before explained (see block description), in the

normal left or right mode one of the lower dar-

lington becomes saturated whereas the other re-

mains open. The upper half of the bridge oper-

ates in the linear mode.

In stop condition both upper bridge darlingtons

are off and both lower are on. In the high output

impedance state the bridge is switched com-

pletely off.

Connecting the motor between pins 9 and 12

both left or right rotation can be obtained. If only

one rotation sense is used the motor can be con-

nected at only one output, by using only the upper

bridge half. Two motors can be connected each

at the each output : in such case they will work al-

ternatively (see application section).

The internal diodes, together with the collector

substrate diodes, protect the output from induc-

tive vol-tage spikes during the transition phase

(fig. 10)

Pin 10

Common sense output. From this pin the output

current of the bridge configuration (motor current)

is fed into RS external resistor in order to gener-

ate a proper voltage drop.

The drop is supplied into pin 1 for tachometric

control and into pin 8 for V/I control (see pin 1 and

pin 8 sections).

Pin 11

Supply voltage.

Pin 12

Output motor right. (see pin 9 section)

Pin 13

Output main amplifier. The voltage on this pin re-

sults from the tachometric speed control and

feeds the output stage.

The value of the capacitor CF (fig. 11), connected

from pins 13 and 14, must be chosen low enough

in order to obtain a short reaction time of the

tachometric loop, and high enough in order to re-

duce the output ripple.

A compromise is reached when the ripple voltage

(peak-to-peak) VROP is equal to 0.1 VMOTOR :

= 2.3

VRIP

( 1 −

)

with VRIP =

VFEM

+ IMOT ⋅ RMOT

and with duty cy-

cle = 50 %. (see pin 2-3 section)

Figure 8.

Figure 9.

Figure 10.

TDA7272A

8/16

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