High power monolithic bridge drivers attractive replacement discrete t

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High power monolithic bridge drivers attractive replacement discrete t

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APPLICATIONS MONOLITHIC BRIDGE DRIVERS
High power monolithic bridge drivers attractive replacement discrete transistors half bridges applications such motor stepper motor driving. This application guide describes three such devices L293, L293E L298 presents practical examples their application.
L293, L293E L298 each contain four pushpull power drivers which used independently more commonly, full bridges. Each driver controlled TTL-level logic input each pair drivers equipped with enable input which controls whole bridge. three devices feature separate logic supply input that logic lower supply voltage, reducing dissipation. This logic supply internally regulated. Additionally, L293E L298 provided with external connections lower emitters each bridge allow connection current sense resistors. L293E separate emitter connections each channel L298 two, each bridge. Figure shows internal structure L293, L293E L298. L293 L293E represented four push pull drivers while internal schematic given L298. Though they drawn differently L293E L298 identical structure L293 differs that does have external emitter connections.
Figure L293, L293E L298 contain four push pull drivers. Each driver controlled logic input each pair bridge) controlled enable input. Additionally, L293E external emitter connections each driver L298 emitter connections each bridge.
AN240/1288
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Figure (continued).
L293 packaged lead POWERDIP package 16-pin with four center leads used conduct heat board copper) handles channel (1.5 peak) voltages L293E, also rated A/36 mounted lead POWERDIP package. 15-lead MULTIWATT plastic power package used L298N which handles channel voltages three devices includes on-chip thermal protection feature high noise immunity. high switching speed makes them particularly suitable switch mode control. PARALLELING OUTPUTS Higher output currents obtained paralleling outputs both bridges. example, outputs L298N connected parallel make single bridge. ensure that current fairly divided between bridges they must connected shown figure other words, channel should paralleled with channel four channel paralleled with channel three. Apart from this rule connection very straightforward inputs, enables, outputs emitters simply connected together. outputs L293 L293E also paralleled this case channel must paralleled with channel channel with channel bridges needed this good idea because L298N used. However, only
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Figure higher currents outputs paralleled. Take care parallel channel with channel channel with channel
bridge required L293 connected single bridge cheaper than underutilized L298N. SHORT CIRCUIT PROTECTION L293 L298N drivers damaged short circuits from output ground supply. Short circuits ground most common protected against circuit shown figure When output short circuited input pulled after delay roughly period determined time constant. upper transistor output stage thus turned off, interrupting short circuit current. When short removed circuit recovers automatically. This shown waveforms figure Note that short circuit removed while high output stays because capacitor charged VIH. system reset falling edge which discharges
Figure This circuit protects driver from output short circuits ground.
Figure Waveforms illustrating short circuit protection provided circuit fig.
MOTOR DRIVING application where rotation always same sense single driver (half bridge) used drive small motor. motor connected either supply ground shown figure only difference between these alternatives that control logic inverted useful fact
remember when minimising control logic. Each device drive four motors connected this way. maximum motor current L293 L298N. However several motors driven continuously care should taken avoid exceeding maximum power dissipation package.
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Each motor this configuration controlled logic input which gives alternatives fast stop (the motor shorted transistors). enable/inhibit inputs also allow free running motor stop turning both transistors driver. Since these inputs common channels (one bridge) this feature only used when both channels disabled together. full bridge configuration used drive motors both directions (figure Using logic inputs channels motor made clockwise, anticlockwise stop rapidly. Figure rotation direction motors driven channel connected supply ground. Figure bridge used bidirectional drive motors.
Inputs Vinh C=L; Vinh
Turn Right Turn Left Fast Motor Stop Free Running Motor Stop
Don't Care
C=X;
High
Vinh
Fast Motor Stop Free Running Motor Stop
High
Fast Motor Stop Free Running Motor Stop
Don't Care
Again, enable/inhibit input used free running stop turns four transistors bridge when low. very rapid stop achieved reversing current, though this requires more careful design stop motor dead. practice tachometer dynamo closed loop control usually necessary. Like previous circuit, this configuration suitable motors with currents (L293/L293E) (L298N). motor speed these examples controlled switching drivers with pulse width modulated squarewaves. This approach particularly suitable microcomputer control. undirectional drive with single channel
control signal applied either channel input appropriate enable input. both cases recirculation path through suppression diode motor, giving fairly slow decay. From practical point view preferable control channel input because circuit response faster. This very convenient because each channel independent input. situation different bidirectional motors driven bridge. this case alternatives have different effects. channel inputs driven signal, with suitable logic, recirculation path through diode, motor transistor (figure 7a), givind slow decay. other hand, enable input controlled recirculation path from ground supply through diodes winding. This path gives faster decay (figure 7b). Figure shows practical example motor speed control. This circuit includes oscillator modulator allows independent regulation speeds motors. channel inputs used control direction. interesting feature this circuit that takes advantage threshold enable/inhibit input economise comparators. TBA820M audio amplifier generates triangle waves, level
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which varied from means Since switching threshold L293's enable/inhibit inputs roughly duty cycle output current (and hence motor speed) controlled setting potentiometer. this circuit switching frequency R1/C1 amplitude oscillator signal divider R2/R3.
Figure current shown solid line interrupted bringing current recirculates round dotted path. Decay slow.
Figure enable input brought interrupt current indicated solid line current recirculates from ground decay faster.
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Figure This circuit illustrates control motor speed. speed each motor controlled independently.
STEPPER MOTOR DRIVING Monolithic bridge drivers extremely useful stepper motor driving because they simplify bipolar motors. This important point since bipolar stepper motor costs less than equivalent unipolar motor fewer windings) gives more torque unit volume, other things being equal. basic configuration bipolar stepper motor driving shown figure this example assumed that suitable translator (phase sequence generator) connected four channel inputs. Either L293 L298N used this circuit L293E would wasted compared L293 because load current regulation, hence sense resistor connection, used. load current requlation highly desirable exploit performance characteristics motor. Using L293E L298N this implemented
adding LM339 quad comparator shown figure This another circuit that requires external translator provides independent chopper regulation current each winding. Looking motor phase one, comparator output initially high, enabling bridge through current motor winding rises until voltage across sensing resistor produces voltage inverting input comparator equal voltage non-inverting input (370 mV). This value produced divider R10/R11 hysteresis determined this point comparator switches, disabling bridge. current winding recirculates through until voltage across falls below lower threshold comparator. comparator then switches again cycle repeats.
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Figure single device used drive phase bipolar stepper motor. operates flip flop. output connected bridge enable inputs (pins normally high, enabling drivers. output current (sensed RS1) reaches double nominal value comparator switches, inhibiting bridges. comparator remains this state until supply interrupted. outputs comparators ORed together that short circuit phase disables both bridges. this circuit should less than voltage input CP1). From value chosen desired phase current sense resistor (and RS2) chosen. current ripple should least avoid spurious triggering CP2. component values indicated motor with resistance /phase, inductance mH/phase current mA/phase. Vref giving when output high when output low. Since current winding reaches peak ripple roughly switching frequency depends hysteresis comparators motor characteristics. this example frequency about kHz. Stepper motor drive circuits simplified using L297 stepper motor controller which contains translator generate phase sequences plus dual chopper regulate phase currents. L297 connects directly L293E L298N shown figure This example drives bipolar stepper motor with winding currents lower currents L293E used more powerful motors driven L298N's with paralleled bridges, giving this configuration motor controlled through L297. step clock moves motor increment, CW/CCW input controls direction HALF/FULL input selects half step normal operation. input Vref connected suitable voltage reference sets peak winding current motor. choppers L297 operate phase lines inhibit lines, depending state logic input called CONTROL. more detailed description L297 "Introducing L297 Stepper Motor Controller".
peak current each winding determined Vref this case switching rate hence average current depends hysteresis comparator R4C4. With component values shown switching frequency roughly kHz. figure circuit uses only half LM339 quad comparator. With adition extra passive components take advantage spare comparators implement short circuit protection. Figure shows this done. before, comparators regulate current windings this case connection different because inhibit/enable inputs used short circuit protection. choppers channel inputs through four clamp diodes D10, D12. This simple trick which allows channel inputs both step sequencing choppers. Comparators realize short circuit protection function. Again looking phase one, compara-
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Figure comparators provide chopper current regulation this bipolar stepper motor drive circuit.
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Figure With quad comparator both current regulation short circuit protection obtained.
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Figure L297 stepper motor controller L298N driver together from complete microprocessorto-stepper motor interface. This circuit drives bipolar stepper motors with winding currents
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Information furnished believed accurate reliable. However, SGS-THOMSON Microelectronics assumes responsibility consequences such information infringement patents other rights third parties which result from use. license granted implication otherwise under patent patent rights SGS-THOMSON Microelectronics. Specifications mentioned this publication subject change without notice. This publication supersedes replaces information previously supplied. SGS-THOMSON Microelectronics products authorized critical components life support devices systems without express written approval SGS-THOMSON Microelectronics. 1995 SGS-THOMSON Microelectronics Rights Reserved SGS-THOMSON Microelectronics GROUP COMPANIES Australia Brazil France Germany Hong Kong Italy Japan Korea Malaysia Malta Morocco Netherlands Singapore Spain Sweden Switzerland Taiwan Thaliand United Kingdom U.S.A.
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High power monolithic bridge drivers attractive replacement discrete t

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