Efficient operation at switching frequencies up to
200 KHz allows a reductionin the size and costof
external filter components. A voltage sense input
and SCR drive output are provided for optional
crowbar overvoltage protection with an external
SCR.
PIN C ONNE CTION (top view)
June 2000
1/22
L296 - L296P
PIN FUNCTIONS
N
°
1CROWBAR INPUTVoltage Sense Input for Crowbar Overvoltage Protection. Normally connected to the
2OUTPUTRegulator Output
3SUPPLY VOLTAGEUnrergulated Voltage Input. An internal Regulator Powers the L296s Internal Logic.
4CURRENT LIMITA resistor connected between this terminal and ground sets the current limiter
5SOFT STARTSoft Start Time Constant. A capacitor is connected between this terminal and ground
6INHIBIT INPUTTTL – Level Remote Inhibit. A logic high level on this input disables the device.
7SYNC INPUTMultiple L296s are synchronized by connecting the pin 7 inputs together and omitting
8GROUNDCommon Ground Terminal
9FREQUENCY
10FEEDBACK INPUTThe Feedback Terminal on the Regulation Loop. The output is connected directly to
11OSCILLATORA parallel RC networki connected to this terminal determines the switching frequency.
12RESET INPUTInput of the Reset Circuit. The threshold is roughly 5 V. It may be connected to the
13RESET DELAYA capacitor connected between this terminal and ground determines the reset signal
14RESET OUTPUTOpen collector reset signal output. This output is high when the supply is safe.
15CROWBAR OUTPUT SCR gate drive output of the crowbar circuit.
NameFunction
feedback input thus triggering the SCR when V
also monitor the input and a voltage divider can be added to increase the threshold.
Connected to ground when SCR not used.
threshold. If this terminal is left unconnected the threshold is internally set (see
electrical characteristics).
to define the soft start time constant. This capacitor also determines the average
short circuit output current.
the oscillator RC network on all but one device.
COMPENSATION
A series RC network connected between this terminal and ground determines the
regulation loop gain characteristics.
this terminal for 5.1V operation ; it is connected via a divider for higher voltages.
This pin must be connected to pin 7 input when the internal oscillator is used.
feedback point or via a divider to the input.
delay time.
exceeds nominal by 20 %. May
out
BLOCK DIAGRAM
2/22
L296 - L296P
CIRCUIT OPERATION
(refer to the block diagram)
The L296 and L296P are monolithic stepdown
erroramplifier,comparatorandtheoutputstage.An
error signal is produced by comparing the output
voltagewithaprecise5.1Von-chipreference(zener
zaptrimmedto ±2%).Thiserrorsignalisthencomparedwiththe sawtoothsignalto generatethefixed
frequencypulsewidthmodulatedpulseswhichdrive
theoutputstage.The gainandfrequencystabilityof
theloopcanbeadjustedby anexternalRCnetwork
connectedtopin9.Closingtheloopdirectlygivesan
outputvoltageof5.1V.Highervoltagesareobtained
by insertinga voltagedivider.
Outputovercurrentsat switch on areprevented by
the soft start function. The error amplifier output is
initially clamped by the externalcapacitorCss and
allowedto rise,linearly,as thiscapacitorischarged
by a constantcurrent source.
Outputoverloadprotectionisprovidedintheformof
a current limiter. The load current is sensed by an
internalmetal resistor connected to a comparator.
Whenthe load current exceedsa presetthreshold
this comparator sets a flip flop which disables the
outputstageanddischargesthesoftstartcapacitor.
A second comparator resetsthe flip flop when the
voltageacross the soft start capacitorhas fallen to
0.4V. The output stage is thus re-enabled and the
output voltage rises under control of the soft start
network.If the overloadconditionisstill presentthe
limiterwill trigger againwhen the thresholdcurrent
is reached.The averageshort circuitcurrent islimitedto a safevalue bythe deadtime introducedby
the softstart network.
The reset circuit generates an output signal when
the supply voltage exceeds a threshold programmed byan externaldivider.Thereset signalis
generatedwitha delaytimeprogrammedby an external capacitor. When the supply falls below the
threshold the reset output goes low immediately.
The resetoutput isan opencollector.
Thescrowbarcircuitsensestheoutputvoltage and
the crowbar outputcan providea currentof 100mA
toswitchonan externalSCR.ThisSCRistriggered
when the output voltage exceeds the nominal by
20%. There is no internal connectionbetween the
outputand crowbarsenseinputthereforethe crowbarcan monitoreitherthe inputor theoutput.
ATTL- levelinhibitinputis providedforapplications
suchasremoteon/offcontrol.Thisinputis activated
byhighlogiclevelanddisablescircuitoperation.After an inhibitthe L296 restartsunder controlof the
softstart network.
The thermaloverloadcircuit disablescircuitoperation when the junction temperature reaches about
150°Candhas hysteresistopreventunstableconditions.
Figure 1 :Reset OutputWaveforms
3/22
L296 - L296P
Figure 2 :Soft StartWaveforms
Figure 3 :CurrentLimiter Waveforms
ABSOLUTE MAXIMUM RATINGS
SymbolParameterValueUnit
V
i
V
i–V2
V
2
V
1,V12
V
15
,V5,V7,V9,V13Voltage at Pins 4, 5, 7, 9 and 135.5V
V
4
,V
V
10
6
V
14
I
9
I
11
I
14
P
tot
,T
T
j
stg
4/22
Input Voltage (pin 3)50V
Input to Output Voltage Difference50V
Output DC Voltage
Output Peak Voltage at t = 0.1µsec f = 200KHz
–1
–7
Voltage at Pins 1, 1210V
Voltage at Pin 1515V
Voltage at Pins 10 and 67V
Voltage at Pin 14 (I14≤ 1 mA)V
i
Pin 9 Sink Current1mA
Pin 11 Source Current20mA
Pin 14 Sink Current (V14< 5 V)50mA
Power Dissipation at T
APPLICATION INFORMATION
Figure 34 : TypicalApplicationCircuit.
(*)Minimumvalue(10 µF) toavoidoscillations; rippleconsideration leads to typicalvalue of 1000 µF or higher L1 : 58930- MPP COGEMA
946044 ; GUP 20 COGEMA946045
SUGGESTEDINDUCTOR
Magnetics 58930 – A2MPP431.0 mm–
Thomson GUP 20 x 16 x 7650.8 mm1 mm
Siemens EC 35/17/10 (B6633& – G0500 – X127)402 x 0.8 mm–
VOGT 250µH Toroidal Coil, Part Number 5730501800
V
0
12 V
15 V
18 V
24 V
(L1)
Core TypeNo TurnsWire GaugeAir Gap
Resistor Values for Standard Output Voltages
R8R7
4.7 KΩ
4.7 K
4.7 K
4.7 K
Ω
Ω
Ω
6.2 KΩ
9.1 K
12 K
Ω
18 K
Ω
Ω
14/22
Figure 35 : P.C.Board and ComponentLayoutof theCircuitof fig.34 (1:1 scale)
L296 - L296P
SELECTIONOF COMPONENT VALUES (see fig. 34)
Component
R1
R2
Recommended
Value
–
100 k
Ω
Purpose
Set Input Voltage
Threshold for Reset.
R34.3 kΩSets Switching Frequency1 kΩ100kΩ
R410 kΩPull-down Resistor22kΩMay be omitted and pin 6 grounded
R515 k
Ω
Frequency Compensation10k
R6Collector Load For Reset
Output
R
R7
R8
iim
–
4.7 kΩ
Divider to Set Output
Voltage
–Sets Current Limit Level7.5kΩIf R
C110µFStability2.2µF
C22.2µFSets Reset Delay––Omitted if reset function not used.
C32.2 nFSets Switching Frequency1 nF3.3nF
C42.2 µFSoft Start1 µF–Also determines average short
C533 nFFrequency Compensation
C6390 pFHigh Frequency
Compensation
C7, C8
L1
100µF
300µH
Output Filter–
Q1Crowbar ProtectionThe SCR must be able to withstand
D1Recirculation Diode7A Schottky or 35 ns t
Allowed Rage
Min.Max.
–
220k
Ω
R1/R2
Notes
V
i min
1
−
5
If output voltage is sensed R1 and
R2 may be limited and pin 12
connected to pin 10.
if inhibit not used.
Ω
V
O
Omitted if reset function not used.
0.05A
–
–
–
R7/R8 =
1kΩ
iim
the current limit is internally fixed.
circuit current.
––Not required for 5 V operation.
–
100µH
the peak discharge current of the
output capacitor and the short
circuit current of the device.
− V
V
O
REF
REF
-
V
is omitted and pin 4 left open
Diode.
rr
15/22
L296 - L296P
Figure 36 : AMinimal5.1 V FixedRegulator.VeryFew Componentsare Required.
Figure 37 : 12V/10 A PowerSupply.
16/22
Figure38 : ProgrammablePower Supply.
Vo= 5.1to 15 V
I
= 4 A max. (min.load current= 100 mA)
o
ripple ≤ 20 mV
loadregulation (1 A to4 A) = 10 mV (V
line regulation(220 V ± 15 % and toI
= 5.1V)
o
= 3 A) = 15 mV (Vo= 5.1 V)
o
L296 - L296P
Figure 39 :
Preregulatorfor Distributed Supplies.
(*)L2 and C2 are necessary to reducethe switching frequency spikes.
17/22
L296 - L296P
Figure 40 : InMultipleSuppliesSeveralL296s
Figure 41 : VoltageSensingforRemote Load.
canbe SynchronizedAs Shown.
Figure 42 : A5.1 V/15 V/24 V MultipleSupply.Note the Synchronizationof theThree L296s.
18/22
L296 - L296P
Figure 43 : 5.1V/2APowerSupply usingExternal
LimitingCurrentResistorand CrowbarProtectionon the SupplyVoltage
(L296Ponly)
SOFT-START AND REPETITIVE POWER-ON
Whenthedeviceisrepetitivelypowered-on,thesoftstart capacitor, C
Information furnished is believed to be accurate and reliable. However, STMicroelectronics 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 STMicroelectronics. Specification mentioned in this
publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written
approval of STMicroelectronics.
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22/22
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