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TDA7272A
HIGH PERFORMANCE MOTOR SPEED REGULATOR
TACHIMETRIC SPEED REGULATION WITH NO NEED FOR AN EXTERNAL SPEED PICKUP V/I SUPPLEMENTARY PREREGULATION DIGITAL CONTROL OF DIRECTION AND MOTOR STOP SEPARATE SPEED ADJUSTMENT 5.5V TO 18V OPERATING SUPPLY VOLTAGE 1A PEAK OUTPUT CURRENT OUTPUT CLAMP DIODES INCLUDED SHORT CIRCUIT CURRENT PROTECTION THERMAL SHUT DOWN WITH HYSTERESIS DUMP PROTECTION (40V) ESD PROTECTION DESCRIPTION TDA7272A are high performance motor speed controller for small power DC motors as used in cassette players. BLOCK DIAGRAM
Powerdip(16+2+2) ORDERING NUMBER: TDA7272A
Using the motor as a digital tachogenerator itself the performance of true tacho controlled systems is reached. A dual loop control circuit provides long term stability 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.
June 1992
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TDA7272A
ABSOLUTE MAXIMUM RATINGS
Symbol VS VS IO Ptot Top Tstg DC Supply Voltage Dump Voltage (300ms) Output Current Power Dissipation at Tpins = 90C at Tamb = 70C Operating Temperature Range Storage Temperature Parameter Value 24 40 Internally limited 4.3 1 -40 to 85 -40 to 150 W W C C Unit V V
PIN CONNECTION (Top view)
THERMAL DATA
Symbol Rth j-amb R th j-pins Parameter Thermal Resistance Junction-ambient Thermal Resistance Junction-pins max. max. Value 80 14 Unit C/W C/W
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TDA7272A
TEST CIRCUIT
A
ELCTRICAL CHARACTERISTICS (Tamb = 25C; VS = 13.5V unless otherwise specified)
Symbol VS IS Parameter Operating Supply Voltage Supply Current No load Test Conditions Min. 5.5 5 Typ. Max. 18 12 Unit V mA
OUTPUT STAGE IO IO V10,9,12 V11,9,12 Output Currente Pulse Output Currente Continuous Voltage Drop Voltage Drop IO = 250mA IO = 250mA 1 250 1.2 1.7 1.5 2 A mA V V
MAIN AMPLIFIER R14 Ib VOFF VR Input Resistance Bias Current Offset Voltage Reference Voltage Internal at non inverting input 100 50 1 2.3 5 K nA mV V
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TDA7272A
ELECTRICAL CHARACTERISTICS (Continued)
Symbol R8 GL VIN1 RIN1 VT Low VT B VT H V2 REF V18,19 Low V18,19 High I18,19 V17,20 REF Parameter Input Resistance Loop Gain Input Allowed Voltage Input Resistance Trigger Level Bias Voltage (pin 1) Trigger Histeresis Reference Voltage Input Low Level Input High Level Input Current Reference Voltage 0 < V18,19 < VS 735 2 2 800 865 750 15 -0.7 500 0 20 10 800 850 0.7 25 Test Conditions Min. 100 9 3 V V mV mV mV V V A mV Typ. Max. Unit K
CURRENT SENSE AMPLIFIER
TRIGGER AND MONOSTABLE STAGE
SPEED PROGRAMMING, DIRECTION CONTROL LOGIC AND CURRENT SOURCE PROGRAMMING
ter, this control principle offers a poor reaction The TDA7272A novel applied solution is based time for motors with a low number of poles. The on a tachometer control system without using realized circuit is extended by a second feed forsuch extra tachometer system. The information of ward loop in order to improve such system by a the actual motor speed is extracted from the mofast auxiliary control path. tor itself. A DC motor with an odd number of poles generates a motor current which contains a fixed This additional path senses the mean output curnumber of discontinuities within each rotation. (6 rent and varies the output voltage according to for the 3 pole motor example on fig. 1) the voltage drop across the inner motor resistance. Apart from a current averaging filter, there Deriving this inherent speed information from the is no delay in such loop and a fast settling behavmotor current, it can be used as a replacement of iour is reached in addition to the long term speed a low resolution AC tachometer system. Because motor accuracy. the settling time of the control loop is limited on principle by the resolution in time of the tachomeFigure 1: Equivalent of a 3 Pole DC Motor (a) and Typical motor Current Waveform (b).
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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 RS ; capacitor CD together with the input impedance of 500 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 hysteresis improves 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 exFigure 2: Application Circuit. 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 logical 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 current matches the mean value of the pulsed monostable current. In this condition the charge of the feedback capacitor becomes constant.
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TDA7272A
The speed n of a k pole motor results : 10.435 n= CT k RP 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 speed for minimum torque ripple. The second fast loop consists of a voltage to current converter which is driven at pin 8 by the low pass filter RL, CL. The output current at this stage is injected by a PNP current mirror into the inner resistor RB. So the driving voltage of the output stage consists of the integrator output voltage plus the fast loop voltage contribution across RB. The power output stage realizes different modes depending on the logic status at pin 18 and 19. - 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 elements are 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 exceeds 150 C. A short circuit protection limits the output current at 1.5 A. Integrated diodes clamp spikes from the inductive load both at VCC and ground. The reference voltages are derived from a common bandgap reference. All blocks are widely supplied by an internal 3.5 V regulator which provides a maximum supply voltage rejection. 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 proper voltage drop. Together with the input resistance at pin 1 [RIN(1) = 500 ] the external capacitor CD realize a high pass filter which differentiates the commutation spikes of the motor current. The trigger 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 variation of motor current : 30mV RS IMOT min. Such value can be too much high for the preregulation stage V-I and it could be necessary to split
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Figure 3.
Figure 4.
them into 2 series resistors RS = RS1 + RS2 (see fig. 4) as explained on pin 8 section. The information can be taken also from an external tachogenerator. Fig. 5 shows various sources connections : the input signal mustn't be lower than 0.7 V.
TDA7272A
Figure 5.
Pin 2 Timing resistor. An internal reference voltage (V2 = 0.8 V) gives possibility to fix by an external resistor (RT), from this pin and ground, the output current amplitude of the monostable circuit, which will be reflected into the timing capacitor (pin 3) ; the typical value would be about 50 A. Figure 6.
Pin 7 Not connected. Pin 8 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 negative resistance output : Rout = - 9 RS (fig. 7) Figure 7.
Pin 3 Timing capacitor. A constant current, determined by the pin 2 resistor, flowing into a capacitor between pin 3 and ground 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 discharged and the pulse width is fixed to the value : Ton = 2.88 RT CT (fig. 6) Pin 4 Not connected. Pin 5 Ground. Connected with pins 6, 15, 16. Pin 6 Ground. Connected with pins 5, 15, 16.
For compensating the motor resistance and avoiding instability : RMOTOR RS 9 The optimization of the resistor RS for the tachometric control must not give a voltage too high for the V/I stage : one solution can be to divide in two parts, as shown in fig. 8, with : RM 30mV and RS1 + RS2 RS2 = 10 I mot min. (see pin 1 sect.) The low pass filter RL, CL must be calculated in 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.
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TDA7272A
Figure 8. substrate diodes, protect the output from inductive vol-tage spikes during the transition phase (fig. 10) Figure 10.
Figure 9.
Pin 10 Common sense output. From this pin the output current of the bridge configuration (motor current) is fed into RS external resistor in order to generate a proper voltage drop. The drop is supplied into pin 1 for tachometric control and into pin 8 for V/I control (see pin 1 and pin 8 sections). Pin 11 Supply voltage. 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 before explained (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 completely off. 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 connected at only one output, by using 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
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Pin 12 Output motor right. (see pin 9 section) Pin 13 Output main amplifier. The voltage on this pin results from the tachometric speed control and feeds the output stage. The value of the capacitor CF (fig. 11), connected from pins 13 and 14, must be chosen low enough in order to obtain a short reaction time of the tachometric loop, and high enough in order to reduce the output ripple. A compromise is reached when the ripple voltage (peak-to-peak) VROP is equal to 0.1 VMOTOR : CT RT (1- ) CF = 2.3 VRIP RP VFEM + IMOT RMOT and with duty cywith V RIP = 10 cle = 50 %. (see pin 2-3 section)
TDA7272A
Figure 11. Figure 13.
Figure 12.
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 CA and RA must been chosen experimentally as follows: - Increase of 10 % the speed with respect to the nominal value by connecting in parallel to Rp a resistor with value about 10 time larger. - Vary the RA and CA values in order to obtain at pin 13 a voltage signal with short response time and without oscillations. Fig. 13 shows the step response at pin 13 versus RA and C A values. Pin 14
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TDA7272A
Figure 14. Figure 15.
Inverting input of main amplifier. In this pin the current reference programmed at pins 20, 17 is compared with the current from the monostable (stream of rectangular pulses). In steady-state condition (constant motor speed) the values are equal and the capacitor CF voltage is constant. This means for the speed n (min 1): 10.435 n= CT k RP where "k" is the number of collector segments. (poles) The non inverting input of the main amplifier is internally connected to a reference voltage (2.3 V). Pin 15 Ground.
Figure 16.
Figure 17. Pin 16 Ground. Pin 17 Left speed adjustment. The voltage at this pin is fixed to a reference value 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 monostable in order to fix the speed of the motor at the programmed value. The correct value of Rp would be : 10.435 RP = CT k n n = motor speed, (min -1) k = poles number The control of speed can be done in different way: - speed separately programmed in two senses of rotation (fig. 14-15) ; - only one speed for the two senses of rotation (fig. 16) ;
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- speeds of the two senses a bit different (i.e. for compensating different pulley effects) (fig. 17) ; - speed programmed with a DC voltage (fig. 18) i.e. with DA converter ;
TDA7272A
- fast forward, by putting a resistor. In this case it is necessary that also at the higher speed for the duty cycle to be significately less than 1 (see value of RT, CT on pin 2, pin 3 sections). Fig. 19 shows the function controlled with a P. Figure 18. Figure 19.
The typical value of the threshold (L-H) is 1.2 V. Pin 19 Left function control. (see pin 18 sect). Pin 20 Right speed adjustment. (see pin 17 sect).
Pin 18 Right function control. The voltages applied to this pin and to pin 19 determine the function, as showed in the table.
CONDITION Pin 18 L H L H Pin 19 L L H H
OUTPUT FUNCTION STOP LEFT RIGHT OPEN
OUTPUT VOLTAGE Pin 12 Pin 9 LOW LOW REG LOW LOW REG HIGH IMP. HIGH IMP.
Figure 20: Typical application.
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Figure 21: Tacho only speed regulation.
Figure 22: One direction regulator of one motor , or alternatively of two motors.
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TDA7272A
Figure 23: P.C. board and components layout of the circuits of Figg. 20, 21, 22.
A
APPLICATION SUGGESTION (Fig. 20,21,22) - (For a 2000 r.p.m. 3 pole DC motor with RM = 16)
Components R S1 R S2 RL; CL Recommended value 1 1.5 22K - 68nF Purpose Current sensing tacho loop. Current sensing V/I loop. Spike filtering. Instability may occur. Slow V/I regulator response. If larger If smaller Tacho loop do not regulate Motor regulator; undercompens. High output ripple. 33nF 67K 100nF 30KW Allowed range Min. 0 0 R MOT/9 Max.
CD R T; CT
68nF 15K - 47nF
Pulse transf. Current source programming to obtain a 50% duty cycle Set of speed. Optimization of integrator ripple and loop response time. Fast response with no overshoot. Low speed. Lower ripple, slower tacho regulator response. High speed Higher ripple, faster response.
R P1; RP2 CF
47K trim. Polyester 100nF
0 10nF 470nF
RA; CA
220K - 220nF
Depending on electrmechanical system.
10nF
470nF
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TDA7272A
Figure 24: Speed regulation vs. supply voltage (circuit of fig. 20).
Figure 26: In connection with a Presettable Counter and I/O peripheral the TDA7271A/TDA7272Acontrols the speed through a D/A Converter.
TDA7272A
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POWERDIP 20 PACKAGE MECHANICAL DATA
DIM. MIN. a1 B b b1 D E e e3 F I L Z 3.30 1.27 8.80 2.54 22.86 7.10 5.10 0.130 0.050 0.38 0.51 0.85 0.50 0.50 24.80 0.346 0.100 0.900 0.280 0.201 0.015 1.40 mm TYP. MAX. MIN. 0.020 0.033 0.020 0.020 0.976 0.055 inch TYP. MAX.
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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 its use. 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. (c) 1994 SGS-THOMSON Microelectronics - All Rights Reserved SGS-THOMSON Microelectronics GROUP OF COMPANIES Australia - Brazil - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco - The Netherlands - Singapore Spain - Sweden - Switzerland - Taiwan - Thaliand - United Kingdom - U.S.A.
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