L292

L292 STMICROELECTRONICS | Alldatasheet

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SWITCH-MODE DRIVER FOR DC MOTORS DRIVING CAPABILITY : 2 A, 36 V, 30 KHz

2 LOGIC CHIP ENABLE

EXTERNAL LOOP GAIN ADJUSTEMENT SINGLE POWER SUPPLY (18 TO 36 V) INPUT SIGNAL SYMMETRIC TO GROUND THERMAL PROTECTION

DESCRIPTION

The L292 is a monolithic LSI circuit in 15-lead Multiwatt ® package. It is intended for use, together with L290 and L291, as a complete 3-chip motor positioning system for applications such as car- riage/daisy-wheel position control in type-writes. The L290/1/2 system can be directly controlled by a microprocessor. March 1993 Symbol Parameter Value Unit Vs Power Supply 36 V Vi Input Voltage - 15 to + Vs V Vinhibit Inhibit Voltage 0 to Vs V Io Output Current 2.5 A Ptot Total Power Dissipation (Tcase = 75 °C) 25 W Tstg Storage and Junction Temperature - 40 to + 150 °C ABSOLUTE MAXIMUM RATINGS CONNECTION DIAGRAM (top view) Vinhibit Output Stage Condition Pin 12 Pin 13 L L Disabled L H Normal Operation H L Disabled H H Disabled TRUTH TABLE ORDER CODE : L292 Multiwatt 15

BLOCK DIAGRAM AND TEST CIRCUIT Symbol Parameter Value Unit Rth-j-case Thermal resistance junction-case Max 3 °C/W THERMAL DATA Symbol Parameter Test conditions Min. Typ. Max. Unit Vs Supply Voltage 18 36 V Id Quiescent Drain Current V s = 20 V (offset null) 30 50 mA Vos Input Offset Voltage (pin 6) I o = 0 ±350 mV Vinh Inhibit Low Level (pin 12, 13) 2 V Inhibit High Level (pin 12, 13) 3.2 V Iinh Low Voltage Condition V inh(L) = 0.4 V - 100 µA High Voltage Conditions V inh(H) = 3.2 V 10 µA Ii Input Current (pin 6) V l = -8.8 V Vl = +8.8 V -1.8 0.5 mA mA Vi Input Voltage (pin 6) R s1 = Rs2 = 0.2Ω Io = 2A 9.1 V I o = -2A -9.1 V Io Output Current Vl = ± 9.8 V Rs1 = Rs2 = 0.2 Ω± 2 A VD Total Drop Out Voltage (inluding sensing resistors) Io = 2 A I o = 1 A 3.5 V VRS Sensing Rsistor Voltage Drop Tj = 150°C Io = 2 A 0.44 V Io Vi Transconductance R s1 = Rs2 =0.2Ω 205 220 235 mA/V R s1 = Rs2 = 0.4Ω 120 mA/V fosc Frequency Range (pin 10) 1 30 KHz ELECTRICAL CHARACTERISTICS (Vs = 36 V, Tamb = 25 °C, fosc = 20 KHz unless otherwise specified) L292

Figure 1. System Block Diagram speed, high-accurancy positioning. speed but under closed-loop control. to set the initial position. and are supplied to the FTA/FTB inputs on the L290. VMA and VMB which are fed to the multipliers.

The second input to each multipler consists of the sign of the first input of the other multiplier before differentiation, these are obtained using the compa- rators C s1 and Cs2. The multiplier outputs, CSA and C SB , are summed by A3 to give the final output signal TACHO. The peak-topeak ripple signal of the TACHO can be found from the following expression: V ripple p − p = π 4 ( √ 2 − 1 ) • Vthaco DC The max value of TACHO is: Vtacho max = π 4 √ 2 • Vthaco DC Using the coparators C1 and C2 another two signals from VAA and VAB are derived - the logic signals STA and STB. This signals are used by the microprocessor to determine the position by counting the pulses. The L2910 internal reference voltage is also derived from V AA and VAB : Vref = | VAA | + | VAB | This reference is used by the D/A converter in the L291 to compensate for variations in input levels, temperature changes and ageing. The "one pulse per rotation" opto encoder output is connected to pin 12 of the L290 (FTF) where it is squared to give the STF logic output for the micro- processor. The TACHO signal and V ref are sent to the L291 via filter networks R8 C8 R9 and R6 C7 R7 respectively. Pin 12 of this chip is the main summing point of the system where TACHO and the D/A converter output are compared. The input to D/A converter consists of 5 bit word plus a sign bit supplied by the microprocessor. The sign bit represets the direction of motor rotation. The (analogue) output of the D/A conveter - DAC/OUT - is compared with the TACHO signal and the risulting error signal is amplified by the error amplifier, and subsequently appears on pin 1. The ERRV sognal (from pin 1 , L291) is fed to pin 6 of the final chip, the L292 H-bridge motor-driver. This input signals is bidirectional so it must be converted to a positive signal bacause the L292 uses a single supply voltage. This is accomplished by the first stage - the level shifter, which uses an internally generated 8 V reference. This same reference voltage supplies the triangle wave oscillator whose frequency is fixed by the external RC network (R 20, C17 - pins 11 and 10) where: 1 fosc = 1 2RC (with R ≥ 8.2 K Ω ) The oscillator determines the switching frequency of the output stage and should be in the range 1 to 30 KHz. Motor current is regulated by an internal loop in the L292 which is performed by the resistors R 18, R19 and the differential current sense amplifier, the out- put of which is filtered by an external RC network and fed back to the error amplifier. The choise of the external components in these RC network (pins 5, 7, 9) is determined by the motor type and the bandwidth requirements. The values shown in the diagram are for a 5Ω , 5 MH motor. (See L292 Transfer Function Calculation in Appli- cation Information). The error signal obtained by the addition of the input and the current feedback signals (pin 7) is used to pulse width modulate the oscillator signal by means of the comparator. The pulse width modulated sig- nal controls the duty cycle of the Hbridge to give an output current corresponding to the L292 input signal. The interval between one side of the bridge switch- ing off and the other switching on, τ, is programmed by C 17 in conjuction with an internal resistor Rτ. This can be foud from: τ = Rτ • Cpin 10. (C 17 in the diagram) Since Rτ is approximately 1.5 KΩ and the recom- mended τ to avoid simultaneous conduction is 2.5 µs Cpin 10 should be around 1.5 nF . The current sense resistors R18 and R19 should be high precision types (maximum tolerance ± 2 %) and the recommended value is given by: R max • Io max ≤ 0.44 V It is possible to synchronize two L292 ’s, if desired, using the network shown in fig. 2. Finally, two enable inputs are provited on the L292 (pins 12 and 13-active low and high respectively). Thus the output stage may be inhibited by taking pin 12 high or by taking pin 13 low. The output will also be inhibited if the supply voltage falls below 18 L292

• 1 Rs = 0.044 R s [ A V ] ( 4 ) OPEN-LOOP GAIN AND STABILITY CRITERION For RC = LM / RM , the open loop gain is: Aβ = 1 sR subF C • G mo Rs R 4 R F 1 + s RF CF = G mo Rs R 4 C 1 s (1 + s RF CF) ( 5 ) In order to achieve good stability, the phase margin must be greater than 45° when | Aβ | = 1. That means that, at fF = 1 2 π RF CF must be | Aβ | < 1 (see fig. 7), that is : | A β | f = 1 2 π RF CF = G mo Rs R 4 C RF CF √ 2 < 1 ( 6 )

Figure 7. Open Loop Frequency Response

a) Small - signals analysis.

4 RF CF Gmo Rs

the system response to an input step signal.

4 RF C F

(where Vi is the amplitude of the input step).

2 RF CF

2 RF CF ) Vi

Figure 8. Small Signal Step Response

It is possible to verify that the L292 works in "closed- loop" conditions during the entire motor current rise-time: the voltage at pin 7 inverting input of the error amplifier) is locked to the reference voltage V R , present at the non-inverting input of the same amplifier. The previous linear analysis is correct for this ex- ample. Descresing the ξ value, the rise-time of the current decreases. But for a good stability, from relationship (6), the maximum value of ξ is: CLOSED LOOP SYSTEM BANDWIDTH. A good choice for x is the value 1 / √2. In this case : I M VI (s) = 0.044 R s 1 + s RF CF 1 + 2s RF CF + 2s 2 RF 2 CF 2 The module of the transfer function is : | IM VI | = 0.044 R s The cutoff frequency is derived by the expression (9) by putting | IM VI | = 0.707 • 0.044 R s (−3 dB), from which : ω T = 0.9 R F CF f T = 0.9 2π R F CF ξmin = 1 √ 2 (phase margin = 45°) b) Large signal reponse The large step signal response is limited by slew- rate and inductive load. In this case, during the rise-time of the motor current, The L292 works is open-loop condition. (8) (9) L292

Example : a) Data - Motors characteristics: LM = 5 mH RM = 5 W LM / RM = 1msec - Voltage and current characteristics: V s = 20 V I M = 2 A VI = 9.1 V - Closed loop bandwidth : 3 kHz b) Calculation - From relationship (4) : R s = 0.044 IM VI = 0.2 Ω and from (1) : G mo = 2VS RM VR = 1 Ω −1 - RC = 1 msec [from expression (2) ]. - Assuming ξ = 1/ √2 ; from (7) follows : ξ2 = 1 2 = 400 C 4R F CF • 0.2 - The cutoff frequency is : f T = 143 • 10−3 R F CF = 3 kHz c) Summarising - RC = 1.10-3 sec - 1000 C RF CF = 1 - RF CF ≅ 47 µs C = 47 nF R = 22 KΩ For RF = 510 Ω → CF = 92 nF L292

DIM. mm inch A 5 0.197 B 2.65 0.104 C 1.6 0.063 D 1 0.039 E 0.49 0.55 0.019 0.022 F 0.66 0.75 0.026 0.030 H1 19.6 0.772 H2 20.2 0.795 L2 17.65 18.1 0.695 0.713 L7 2.65 2.9 0.104 0.114 S 1.9 2.6 0.075 0.102 S1 1.9 2.6 0.075 0.102 Dia1 3.65 3.85 0.144 0.152 MULTIWATT15 PACKAGE MECHANICAL DATA L292

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. © 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. L292