SGS Thomson Microelectronics TDA7272A Datasheet
HIGH PERFORMANCE MOTOR SPEED REGULATOR
TACHIMETRIC SPEED REGULATION WITH
NO NEED FOR AN EXTERNAL SPEED PICKUP
V/I SUPPLEMENTARYPREREGULATION
DIGITAL CONTROL OF DIRECTION AND
MOTORSTOP
SEPARATESPEEDADJUSTMENT
5.5V TO 18V OPERATING SUPPLY VOLTAGE
1A PEAK OUTPUT CURRENT
OUTPUTCLAMP DIODESINCLUDED
SHORTCIRCUIT CURRENT PROTECTION
THERMAL SHUT DOWNWITH HYSTERESIS
DUMP PROTECTION (40V)
ESD PROTECTION
TDA7272A
Powerdip(16+2+2)
ORDERING NUMBER: TDA7272A
DESCRIPTION
TDA7272A are high performance motor speed
controller for small power DC motors as used in
cassetteplayers.
BLOCK DIAGRAM
Using the motor as a digital tachogenerator itself
the performance of true tacho controlled systems
isreached.
A dual loop control circuit provides long term stabilityand fast settling behaviour.
This is advanced information on a new product now in developmentor undergoing evaluation.Details aresubject to changewithout notice.
June 1992
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TDA7272A
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
V
S
V
S
I
O
P
tot
T
op
T
stg
PIN CONNECTION (Topview)
DC Supply Voltage 24 V
Dump Voltage (300ms) 40 V
Output Current Internally limited
Power Dissipation at T
at T
pins
amb
=90°C
=70°C
4.3
1
Operating Temperature Range -40 to 85 °C
Storage Temperature -40 to 150 °C
W
W
THERMAL DATA
Symbol Parameter Value Unit
Thermal Resistance Junction-ambient max. 80 °C/W
Thermal Resistance Junction-pins max. 14 °C/W
2/16
R
th j-amb
R
th j-pins
TEST CIRCUIT
TDA7272A
A
ELCTRICAL CHARACTERISTICS (T
=25°C; VS=13.5V unless otherwisespecified)
amb
Symbol Parameter Test Conditions Min. Typ. Max. Unit
V
I
Operating Supply Voltage 5.5 18 V
S
Supply Current No load 5 12 mA
S
OUTPUT STAGE
V
10,9,12
V
11,9,12
I
I
Output Currente Pulse 1 A
O
Output Currente Continuous 250 mA
O
Voltage Drop IO= 250mA 1.2 1.5 V
Voltage Drop IO= 250mA 1.7 2 V
MAIN AMPLIFIER
R
V
OFF
V
Input Resistance 100 KΩ
14
I
Bias Current 50 nA
b
Offset Voltage 1 5 mV
Reference Voltage Internal at non inverting input 2.3 V
R
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TDA7272A
ELECTRICAL CHARACTERISTICS (Continued)
Symbol Parameter Test Conditions Min. Typ. Max. Unit
CURRENT SENSE AMPLIFIER
R
G
TRIGGER AND MONOSTABLE STAGE
V
R
V
T Low
V
V
V
2 REF
SPEED PROGRAMMING, DIRECTION CONTROL LOGICAND CURRENT SOURCE PROGRAMMING
V
18,19Low
V
18,19 High
I
18,19
V
17,20 REF
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 motor itself. A DC motorwith 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
principleby the resolution in time of the tachome-
Figure1: Equivalent of a 3Pole DC Motor (a) and Typical motor CurrentWaveform (b).
Input Resistance 100 KΩ
8
Loop Gain 9
L
Input Allowed Voltage -0.7 3 V
IN1
Input Resistance 500 Ω
IN1
Trigger Level 0 V
Bias Voltage (pin 1) 15 20 25 mV
TB
Trigger Histeresis 10 mV
TH
Reference Voltage 750 800 850 mV
Input Low Level 0.7 V
Input High Level 2 V
Input Current 0 < V
Reference Voltage 735 800 865 mV
18,19<VS
2 µA
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 forward loop in order to improve such system by a
fastauxiliary control path.
This additional path senses the mean output current and varies the output voltage according to
the voltage drop across the inner motor resistance. Apart from a current averaging filter, there
is no delay in such loop and a fast settling behaviour is reached in addition to the long term speed
motoraccuracy.
4/16
TDA7272A
BLOCK DESCRIPTION
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 R
; capacitor CD together
S
with the input impedance of 500 Ω at pin 1 realizes a high pass filter.
This pin is internally biased at 20 mV, each negative zero transition switches the input comparator.
A 10 mV hysteresisimproves the noise immunity.
The trigger circuit is followed by an internal delay
time differentiator.
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-
Figure2: ApplicationCircuit.
ternalelements CT and RT.
The monostable is retriggerable ; this function
prevents the system from fault stabilization at
higherharmonics 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.
ResistorRP1 and RP2 define the speed, the logicalinputs are at pin 18 and 19.
At the invertinginput (pin 14) of the main amplifier
the referencecurrent is compared with the pulsed
monostableoutput current.
For the correct motor speed, the reference current matches the mean value of the pulsed
monostable current. In this condition the charge
of the feedbackcapacitorbecomes constant.
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