HIGH PERFORMANCE MOTOR SPEED REGULATOR
TACHIMETRIC SPEED REGULATION WITH
NO NEED FOR AN EXTERNAL SPEED PICK-
V/I SUPPLEMENTARY PREREGULATION
DIGITAL CONTROL OF DIRECTION AND
SEPARATE SPEED ADJUSTMENT
5.5V TO 18V OPERATING SUPPLY VOLT-
1A PEAK OUTPUT CURRENT
OUTPUT CLAMP DIODES INCLUDED
SHORT CIRCUIT CURRENT PROTECTION
THERMAL SHUT DOWN WITH HYSTERESIS
DUMP PROTECTION (40V)
TDA7272A are high performance motor speed
controller for small power DC motors as used in
Using the motor as a digital tachogenerator itself
the performance of true tacho controlled systems
A dual loop control circuit provides long term sta-
bility and fast settling behaviour.
This is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
ORDERING NUMBER: TDA7272A
ABSOLUTE MAXIMUM RATINGS
DC Supply Voltage
Dump Voltage (300ms)
Power Dissipation at Tpins =90
at Tamb =70
Operating Temperature Range
-40 to 85
-40 to 150
Thermal Resistance Junction-ambient
Thermal Resistance Junction-pins
PIN CONNECTION (Top view)
ELCTRICAL CHARACTERISTICS (Tamb =25
°C; VS = 13.5V unless otherwise specified)
Operating Supply Voltage
Output Currente Pulse
Output Currente Continuous
IO = 250mA
IO = 250mA
Internal at non inverting input
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
ELECTRICAL CHARACTERISTICS (Continued)
CURRENT SENSE AMPLIFIER
TRIGGER AND MONOSTABLE STAGE
Input Allowed Voltage
Bias Voltage (pin 1)
SPEED PROGRAMMING, DIRECTION CONTROL LOGIC AND CURRENT SOURCE PROGRAMMING
Input Low Level
Input High Level
0 < V18,19 <VS
Figure 1: Equivalent of a 3 Pole DC Motor (a) and Typical motor Current Waveform (b).
The principle structure of the element is shown in
fig. 2. As to be seen, the motor speed information
is derived from the motor current sense drop
across the resistors RS ; capacitor CD together
with the input impedance of 500
at pin 1 real-
izes a high pass filter.
This pin is internally biased at 20 mV, each nega-
tive zero transition switches the input comparator.
A 10 mV hysteresis improves the noise immunity.
The trigger circuit is followed by an internal delay
Thus, the system becomes widely independent of
the applied waveform at pin 1, the differentiator
triggers a monostable circuit which provides a
constant current duration. Both, output current
magnitude and duration T, are adjustable by ex-
ternal elements CT and RT.
The monostable is retriggerable ; this function
prevents the system from fault stabilization at
higher harmonics of the nominal frequency.
The speed programming current is generated by
two separate external adjustable current sources.
A corresponding digital input signal enables each
current source for left or right rotation direction.
Resistor RP1 and RP2 define the speed, the logi-
cal inputs are at pin 18 and 19.
At the inverting input (pin 14) of the main amplifier
the reference current is compared with the pulsed
monostable output current.
For the correct motor speed, the reference cur-
rent matches the mean value of the pulsed
monostable current. In this condition the charge
of the feedback capacitor becomes constant.
Figure 2: Application Circuit.