Datasheet TDA7272A Datasheet (SGS Thomson Microelectronics)

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

1/16

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

3/16

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

TDA7272A

The speedn of a k pole motor results :

10.435

n =

C

TkRP

and becomes independent of the resistor RT
which only determines the current level and the
duty cycle which should be 1 : 1 at the nominal
speedfor minimumtorque ripple.

The second fast loop consists of a voltage to cur­rent converter which is driven at pin 8 by the low
pass filter R

. The output current at this stage

L,CL

is injected by a PNP current mirror into the inner
resistor R

. So the driving voltage of the output

B

stage consists of the integrator output voltage
plus the fastloop voltagecontribution across R

.

B

The power output stage realizes different modes
dependingon the logic status at pin 18 and19.

- Normal operation for left and right mode :
each upper TR of the bridge is used as
voltage follower whereas the lower acts as
a switch.

- Stop mode where the upper half is open
and the lower is conductive.

- High impedance status where all power
elementsare switched-off.

The high impedance status is also generated
when the supply voltage overcomes the 5 V to 20
V operating range or when the chip temperature
exceeds150 °C.

A short circuit protection limits the output current
at 1.5 A. Integrated diodes clamp spikes from the
inductiveload both at V

and ground.

CC

The reference voltages are derived from a com­mon bandgap reference. All blocks are widely
suppliedby an internal 3.5 V regulator which pro­videsa maximum supply voltage rejection.

Figure3.

Figure4.

PIN FUNCTION AND APPLICATION INFORMA­TION

PIN 1
Trigger input. Receives a proper voltage which

contains the information of the motor speed. The
waveform can be derived directly by the motor
current (fig. 3). The external resistor generates a
propervoltage drop. Togetherwith the input resis­tance at pin 1 [R
pacitorC

realizea high passfilter which differen-

D

(1) = 500 Ω ] the external ca-

IN

tiates the commutation spikes of the motor
current. Thetrigger level is 0V.

The biasing of the pin 1 is 20 mV with a hystere­sis of 10 mV. So the sensing resistance must be
chosen high enough in order to obtain a negative
spike of the least 30 mV on pin 1, also with mini­mum variationof motor current :

S

∆I

MOT

min.

30mV

≥

R

Such value can be too much high for the preregu­lation stage V-I and it could be necessary to split

6/16

them into 2 series resistors R

=RS1+RS2(see

S

fig. 4) as explained on pin 8 section.
The information can be taken also from an exter-

nal tachogenerator.Fig. 5 shows various sources
connections:

the input signal mustn’t be lower than 0.7 V.

Figure5.

TDA7272A

Pin 2

Timing resistor. An internal reference voltage
(V2 = 0.8 V) gives possibility to fix by an external
resistor (R

), from this pin and ground, the output

T

current amplitudeof the monostable circuit, which
will be reflected into the timing capacitor (pin 3) ;
the typicalvalue would be about 50 µ A.

Figure6.

Pin 3

Timing capacitor. A constant current, determined
by the pin 2 resistor, flowing into a capacitor be­tween pin 3 andground 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 dis­chargedand the pulsewidth is fixed to the value :

= 2.88 RTCT(fig.6)

T

on

Pin 4

Not connected.

Pin 5

Ground.Connected with pins6, 15, 16.

Pin 6

Ground.Connected with pins5, 15, 16.

Pin7

Notconnected.

Pin8

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
negativeresistanceoutput :

R

= −9RS(fig. 7)

out

Figure7.

For compensating the motor resistance and
avoidinginstability:

R

MOTOR

≤

R

S

The optimization of the resistor R

9

for the tacho-

S

metric controlmust not give a voltage too high for
the V/I stage : one solutioncan be to divide in two
parts, as shown in fig.8, with :

R

M

=

R

S2

10

and R

+ RS2≥

S1

30mV

∆ I mot min.

(seepin 1 sect.)

The low pass filter R

must be calculated in

L,CL

order to reduce the ripple of the motor commuta­tion 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 radia­tion.

7/16

TDA7272A

Figure8.

Figure9.

substrate diodes, protect the output from induc­tive vol-tage spikes during the transition phase
(fig.10)

Figure10.

Pin10

Common sense output. From this pin the output
current of the bridge configuration (motor current)
is fed into R

external resistor in order to gener-

S

ate a propervoltagedrop.
The drop is supplied into pin 1 for tachometric

control andinto pin 8 for V/I control (see pin 1 and
pin 8 sections).

Pin 9

Output motor left. The four power transistors are
realized as darlington structures. The arrange­ment is controlled by the logic status at pins 18
and 19.

As beforeexplained (see block description), in the
normal left or right mode one of the lower dar­lington becomes saturated whereas the other re­mains open. The upper half of the bridge oper­ates in the linear mode.

In stop condition both upper bridge darlingtons
are off and both lower are on. In the high output
impedance state the bridge is switched com­pletelyoff.

Connecting the motor between pins 9 and 12
both left or right rotation can be obtained. If only
one rotation sense is used the motor can be con­nectedat only one output, byusing only the upper
bridge half. Two motors can be connected each
at the each output : in such case they will work al­ternatively(see application section).

The internal diodes, together with the collector

8/16

Pin11

Supplyvoltage.

Pin12

Outputmotor right. (seepin 9 section)

Pin13

Output main amplifier. The voltage on this pin re­sults from the tachometric speed control and
feedsthe output stage.

The value of the capacitorC

(fig. 11), connected

F

from pins 13 and 14, must be chosen low enough
in order to obtain a short reaction time of the
tachometricloop, and high enough in order to re­duce the output ripple.

A compromise is reached when the ripple voltage
(peak-to-peak)V

C

F

V

FEM

RIP

=

withV
cle = 50 %. (see pin 2-3 section)

is equal to 0.1 V

ROP

= 2.3

+ I

MOT

C

V

RIP

⋅ R

10

T

( 1 −

MOT

MOTOR

R

T

)

R

P

and with duty cy-

:

TDA7272A

Figure11.

Figure12.

Figure13.

In order to compensate the behaviour of the
whole system regulator-motor-load (considering
axis friction, load torque, inertias moment of the
motor of the load. etc.) a RC series network is
also connected between pins 13 and 14 (fig. 12).
The value of C

and RAmust been chosen ex-

A

perimentallyas follows:

- Increase of 10 % the speed with respect to
the nominal value by connecting in parallel
to R

a resistor with value about 10 time

p

larger.

- Vary the R

and CAvalues in order to ob-

A

tain at pin 13 a voltage signal with shortre­sponse time and without oscillations. Fig.
13 shows the step response at pin 13 ver­sus R

andCAvalues.

A

Pin 14

9/16

TDA7272A

Figure14. Figure15.

Inverting input of main amplifier. In this pin the
current reference programmed at pins 20, 17 is
compared with the current from the monostable
(streamof rectangularpulses).

In steady-state condition (constant motor speed)
the values are equal and the capacitor C

voltage

F

is constant.
This means for the speed n (min 1):

10.435

=

n

C

TkRP

where ”k” is the number of collector segments.
(poles)

The non inverting input of the main amplifier is in­ternallyconnected to a referencevoltage (2.3 V).

Pin 15

Ground.

Pin 16

Ground.

Pin 17

Left speed adjustment. The voltage at this pin is
fixed to a referencevalue of 0.8 V. A resistor from
this pin and ground (fig. 14) fixes the reference
current which will be compared with the medium
output current of the monostablein order to fix the
speed of the motor at the programmed value.The
correct value of R

would be :

p

10.435

=

R

P

C

kn

T

n = motor speed, (min -1)
k = poles number

The control of speed can be done in different
way:

- speed separately programmed in two
sensesofrotation (fig. 14-15) ;

- only one speed for the two senses of rota­tion (fig. 16) ;

Figure16.

Figure17.

- speeds of the two sensesa bit different(i.e.
for compensating different pulley effects)
(fig. 17) ;

- speed programmed with a DC voltage (fig.

18)i.e. with DA converter;

10/16

TDA7272A

- fast forward, by putting a resistor. In this

Figure19.

case it is necessary that also at the higher
speed for the duty cycle to be significately
less than 1 (see value of R

T,CT

on pin 2,

pin 3 sections).

Fig. 19 shows the functioncontrolled with a µP.

Figure18.

Thetypical value of the threshold (L-H) is 1.2 V.

Pin19

Left functioncontrol. (see pin 18 sect).

Pin 18

Right functioncontrol. The voltagesapplied to this

Pin20

Rightspeed adjustment. (seepin 17 sect).

pin and to pin 19 determine the function, as
showed in the table.

CONDITION

Pin 18 Pin 19 Pin 12 Pin 9

L

H

L

H

L

L
H
H

OUTPUT FUNCTION

STOP

LEFT

RIGHT

OPEN

OUTPUT VOLTAGE

LOW
LOW

REG

HIGH IMP.

HIGH IMP.

LOW
REG
LOW

Figure20: Typicalapplication.

11/16

TDA7272A

Figure21: Tachoonly speed regulation.

Figure22: One direction regulatorof one motor , or alternatively of two motors.

12/16

Figure23: P.C.board and componentslayout of the circuits of Figg. 20, 21, 22.

A

TDA7272A

APPLICATIONSUGGESTION (Fig.20,21,22) - (For a 2000 r.p.m. 3 pole DC motor with R

Components

R

S1

R

S2

R

L;CL

C

D

R

T;CT

R

P1;RP2

C

F

R

A;CA

Recommended

value

1Ω Current sensing

1.5Ω Current sensing

22KΩ - 68nF Spike filtering. Slow V/I

Purpose If larger If smaller

Tacho loop do

tacho loop.

V/I loop.

Instability may
occur.

not regulate
Motor regulator;

undercompens.
High output

regulator

ripple.

response.

68nF Pulse transf. 33nF 100nF

15KΩ - 47nF Current source

programming to
obtain a 50%
duty cycle

47KΩ trim. Set of speed. Low speed. High speed 0

Polyester 100nF Optimization of

integrator ripple
and loop
response time.

220KΩ - 220nF Fast response

with no

Lower ripple,
slower tacho
regulator
response.

Depending on electrmechanical
system.

Higher ripple,
faster response.

overshoot.

Allowed range

Min. Max.

67KΩ 30KW

10nF 470nF

10nF 470nF

=16Ω)

M

0

0R

MOT

/9

13/16

TDA7272A

Figure24: Speedregulation vs. supply voltage

(circuit of fig. 20).

Figure26: In connectionwitha PresettableCounter and I/O peripheralthe TDA7271A/TDA7272Acon-

trols the speedthrough a D/A Converter.

TDA7272A

14/16

POWERDIP 20 PACKAGEMECHANICAL DATA

TDA7272A

DIM.

MIN. TYP. MAX. MIN. TYP. MAX.

a1 0.51 0.020

B 0.85 1.40 0.033 0.055
b 0.50 0.020

b1 0.38 0.50 0.015 0.020

D 24.80 0.976

E 8.80 0.346
e 2.54 0.100

e3 22.86 0.900

F 7.10 0.280

I 5.10 0.201
L 3.30 0.130
Z 1.27 0.050

mm inch

15/16

TDA7272A

Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsibility for the
consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from itsuse. No
license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications men­tioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied.
SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without ex­press written approval of SGS-THOMSON Microelectronics.

 1994 SGS-THOMSON Microelectronics - All RightsReserved

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