Datasheet

Pin 2
Timing resistor. An internal reference voltage
(V2 = 0.8 V) gives possibility to fix by an external
resistor (R
T
), 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 :
T
on
= 2.88 R
T
C
T
(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
negativeresistance output :
R
out
= − 9R
S
(fig. 7)
For compensating the motor resistance and
avoiding instability :
R
S
≤
R
MOTOR
9
The optimization of the resistor R
S
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 :
R
S2
=
R
M
10
and R
S1
+ R
S2
≥
30mV
∆ I mot min.
(see pin 1 sect.)
The low pass filter R
L
,C
L
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
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