TDA7272A Datasheet, PDF (7/16 Pages) STMicroelectronics – HIGH PERFORMANCE MOTOR SPEED REGULATOR

Figure 5.
TDA7272A
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.
Figure 6.
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 :
R_out = − 9 R_S (fig. 7)
Figure 7.
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.
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 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.
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