TDA7272A Datasheet, PDF (4/16 Pages) STMicroelectronics – HIGH PERFORMANCE MOTOR SPEED REGULATOR

TDA7272A
ELECTRICAL CHARACTERISTICS (Continued)
Symbol
Parameter
Test Conditions
Min. Typ. Max. Unit
CURRENT SENSE AMPLIFIER
R8
Input Resistance
100
KΩ
GL
Loop Gain
9
TRIGGER AND MONOSTABLE STAGE
VIN1 Input Allowed Voltage
-0.7
3
V
R_IN1 Input Resistance
500
Ω
VT Low Trigger Level
0
V
VT B Bias Voltage (pin 1)
15
20
25
mV
V_{T H} Trigger Histeresis
10
mV
V_{2 REF} Reference Voltage
750 800 850 mV
SPEED PROGRAMMING, DIRECTION CONTROL LOGIC AND CURRENT SOURCE PROGRAMMING
V_{18,19 Low} Input Low Level
0.7
V
V_{18,19 High} Input High Level
2
V
I18,19 Input Current
0 < V18,19 < VS
2
µA
V_{17,20 REF} Reference Voltage
735 800 865 mV
The TDA7272A novel applied solution is based
on a tachometer control system without using
such extra tachometer system. The information of
the actual motor speed is extracted from the mo-
tor itself. A DC motor with an odd number of poles
generates a motor current which contains a fixed
number of discontinuities within each rotation. (6
for the 3 pole motor example on fig. 1)
Deriving this inherent speed information from the
motor current, it can be used as a replacement of
a low resolution AC tachometer system. Because
the settling time of the control loop is limited on
principle by the resolution in time of the tachome-
ter, this control principle offers a poor reaction
time for motors with a low number of poles. The
realized circuit is extended by a second feed for-
ward loop in order to improve such system by a
fast auxiliary control path.
This additional path senses the mean output cur-
rent and varies the output voltage according to
the voltage drop across the inner motor resis-
tance. Apart from a current averaging filter, there
is no delay in such loop and a fast settling behav-
iour is reached in addition to the long term speed
motor accuracy.
Figure 1: Equivalent of a 3 Pole DC Motor (a) and Typical motor Current Waveform (b).
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