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.

5/16