L296
L296P
April1993
HIGH CURRENT SWITCHING REGULATORS
.4 AOUTPUT CURRENT
.5.1 V TO 40 V OUTPUT VOLTAGERANGE
.0 TO 100 % DUTY CYCLE RANGE
.PRECISE(±2 %)ON-CHIP REFERENCE
.SWITCHING FREQUENCY UP TO 200 KHz
.VERYHIGH EFFICIENCY (UP TO 90 %)
.VERYFEW EXTERNAL COMPONENTS
.SOFTSTART
.RESETOUTPUT
.EXTERNAL PROGRAMMABLE LIMITING
CURRENT (L296P)
.CONTROL CIRCUIT FOR CROWBAR SCR
.INPUT FOR REMOTE INHIBIT AND
SYNCHRONUS PWM
.THERMAL SHUTDOWN
DESCRIPTION
TheL296andL296Parestepdownpowerswitching
regulatorsdelivering 4 Aat a voltagevariable from
5.1 V to 40 V.
Featuresofthedevicesincludesoftstart,remotein-
hibit, thermal protection, a reset output for micro-
processors and a PWM comparator input for syn-
chronizationin multichip configurations.
The L296Pincudesexternalprogrammablelimiting
current.
TheL296and L296Paremountedin a15-leadMul-
tiwattplasticpowerpackageandrequiresveryfew
externalcomponents.
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.
Multiwatt
(15 lead)
ORDERING NUMBERS :
L296 (Vertical) L296HT (Horizontal)
L296P (Vertical) L296PHT (Horizontal)
PIN CONNECTION (top view)
1/21
PIN FUNCTIONS
N°Name Function
1 CROWBAR INPUT Voltage Sense Input for Crowbar Overvoltage Protection. Normally connected to the
feedback input thus triggering the SCR when V out exceeds nominal by 20 %. May
also monitor the input and a voltage divider can be added to increase the threshold.
Connected to ground when SCR not used.
2 OUTPUT Regulator Output
3 SUPPLY VOLTAGE Unrergulated Voltage Input. An internal Regulator Powers the L296s Internal Logic.
4 CURRENT LIMIT A resistor connected between this terminal and ground sets the current limiter
threshold. If this terminal is left unconnected the threshold is internally set (see
electrical characteristics).
5 SOFT START Soft Start Time Constant. A capacitor is connected between this terminal and ground
to define the soft start time constant. This capacitor also determines the average
short circuit output current.
6 INHIBIT INPUT TTL Level Remote Inhibit. A logic high level on this input disables the device.
7 SYNC INPUT Multiple L296s are synchronized by connecting the pin 7 inputs together and omitting
the oscillator RC network on all but one device.
8 GROUND Common Ground Terminal
9 FREQUENCY
COMPENSATION A series RC network connected between this terminal and ground determines the
regulation loop gain characteristics.
10 FEEDBACK INPUT The Feedback Terminal on the Regulation Loop. The output is connected directly to
this terminal for 5.1V operation ; it is connected via a divider for higher voltages.
11 OSCILLATOR A parallel RC networki connected to this terminal determines the switching frequency.
This pin must be connected to pin 7 input when the internal oscillator is used.
12 RESET INPUT Input of the Reset Circuit. The threshold is roughly 5 V. It may be connected to the
feedback point or via a divider to the input.
13 RESET DELAY A capacitor connected between this terminal and ground determines the reset signal
delay time.
14 RESET OUTPUT Open collector reset signal output. This output is high when the supply is safe.
15 CROWBAR OUTPUT SCR gate drive output of the crowbar circuit.
BLOCK DIAGRAM
L296 - L296P
2/21
CIRCUIT OPERATION
(refer to the block diagram)
The L296 and L296P are monolithic stepdown
switching regulatorsprovidingoutputvoltages from
5.1Vto 40V and delivering 4A.
Theregulationloopconsistsofasawtoothoscillator,
erroramplifier,comparatorandtheoutputstage.An
error signal is produced by comparing the output
voltagewithaprecise5.1Von-chipreference(zener
zaptrimmed to±2%).Thiserrorsignalisthencom-
paredwiththesawtoothsignalto generatethe fixed
frequencypulsewidthmodulatedpulseswhichdrive
theoutputstage.Thegainandfrequencystabilityof
theloopcanbeadjustedbyan externalRC network
connectedtopin9.Closingtheloopdirectlygivesan
outputvoltageof5.1V.Highervoltagesareobtained
byinserting a voltagedivider.
Outputovercurrents at switch on are preventedby
the soft start function. The error amplifier output is
initially clamped by the externalcapacitorCss and
allowedto rise, linearly, asthis capacitor is charged
bya constantcurrentsource.
Outputoverloadprotectionis providedin theformof
a current limiter. The load current is sensedby an
internal metal resistor connectedto a comparator.
When the loadcurrent exceedsa preset threshold
this comparator sets a flip flop which disables the
outputstageanddischargesthesoftstartcapacitor.
A second comparator resets the flip flop when the
voltage across the softstart capacitorhas fallen to
0.4V.The output stage is thus re-enabledand the
output voltage rises under control of the soft start
network.If theoverloadcondition is still presentthe
limiterwill triggeragain when the thresholdcurrent
is reached. The averageshort circuit current islim-
ited to a safe value by the dead time introduced by
the softstart network.
The reset circuit generates an output signal when
the supply voltage exceeds a threshold pro-
grammedbyan externaldivider. Theresetsignalis
generatedwitha delaytime programmed byan ex-
ternal capacitor. When the supply falls below the
threshold the reset output goes low immediately.
Thereset outputis anopen collector.
The scrowbar circuit sensesthe output voltageand
the crowbaroutput can providea currentof 100mA
toswitchonanexternalSCR. ThisSCRis triggered
when the output voltage exceeds the nominal by
20%. There is no internal connection between the
outputandcrowbar sense inputthereforethe crow-
bar can monitor either the input or the output.
ATTL -level inhibitinputisprovidedforapplications
suchasremoteon/offcontrol.Thisinputisactivated
byhighlogiclevel anddisablescircuitoperation.Af-
ter an inhibit the L296 restarts under control of the
soft startnetwork.
Thethermaloverload circuit disables circuit opera-
tion when the junction temperature reaches about
150 °C andhashysteresisto preventunstablecon-
ditions.
Figure 1 : Reset Output Waveforms
L296 - L296P
3/21
Figure 2 : SoftStartWaveforms
Figure 3 : CurrentLimiter Waveforms
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
ViInput Voltage (pin 3) 50 V
Vi–V
2Input to Output Voltage Difference 50 V
V2Output DC Voltage
Output Peak Voltage at t = 0.1 µsec f = 200KHz –1
–7 V
V
V
1
,V
12 Voltage at Pins 1, 12 10 V
V15 Voltage at Pin 15 15 V
V4,V
5
,V
7
,V
9
,V
13 Voltage at Pins 4, 5, 7, 9 and 13 5.5 V
V10,V
6Voltage at Pins 10 and 6 7 V
V14 Voltage at Pin 14 (I14 1 mA) Vi
I9Pin 9 Sink Current 1 mA
I11 Pin 11 Source Current 20 mA
I14 Pin 14 Sink Current (V14 < 5 V) 50 mA
Ptot Power Dissipation at Tcase 90 °C20W
T
j
,T
stg Junction and Storage Temperature 40 to 150 °C
L296 - L296P
4/21
THERMAL DATA
Symbol Parameter Value Unit
Rth j-case Thermal Resistance Junction-case Max. 3 °C/W
Rth j-amb Thermal Resistance Junction-ambient Max. 35 °C/W
ELECTRICAL CHARACTERISTICS
(refer to the test circuits Tj=25
o
C, Vi= 35V, unless otherwise specified)
Symbol Parameter Test Conditions Min. Typ. Max. Unit Fig.
DYNAMIC CHARACTERISTICS (pin 6 to GND unless otherwise specified)
VoOutput Voltage Range Vi= 46V, Io=1A V
ref 40 V 4
ViInput Voltage Range Vo=V
ref to 36V, Io3A 9 46 V 4
ViInput Voltage Range Note (1), Vo=V
REF to 36V Io=4A 46 V 4
V
oLine Regulation Vi=10V to 40V, Vo=V
ref,I
o=2A 15 50 mV 4
V
oLoad Regulation Vo=V
ref
Io=2Ato4A
I
o= 0.5A to 4A 10
15 30
45
mV 4
Vref Internal Reference Voltage (pin 10) Vi= 9V to 46V, Io= 2A 5 5.1 5.2 V 4
Vref
TAverage Temperature Coefficient
of Reference Voltage Tj=0°C to 125°C, Io= 2A 0.4 mV/°C
VdDropout Voltage Between Pin 2
and Pin 3 Io=4A
I
o=2A 2
1.3 3.2
2.1 V
V4
4
I2L Current Limiting Threshold (pin 2) L296 - Pin 4 Open,
Vi= 9V to 40V, Vo=V
ref to 36V 4.5 7.5 A 4
L296P - Vi= 9V to 40V, Vo=V
ref
Pin 4 Open
RIim = 22k5
2.5 7
4.5
A4
I
SH Input Average Current Vi= 46V, Output Short-circuited 60 100 mA 4
ηEfficiency Io=3A
V
o=V
ref
Vo= 12V 75
85
%4
SVR Supply Voltage Ripple Rejection Vi=2V
rms,f
ripple = 100Hz
Vo=V
ref,I
o=2A 50 56 dB 4
f Switching Frequency 85 100 115 kHz 4
f
Vi
Voltage Stability of Switching
Frequency Vi= 9V to 46V 0.5 % 4
f
Tj
Temperature Stability of Switching
Frequency Tj=0°C to 125°C1%4
f
max Maximum Operating Switching
Frequency Vo=V
ref,I
o= 1A 200 kHz
Tsd Thermal Shutdown Junction
Temperature Note (2) 135 145 °C–
DC CHARACTERISTICS
I3Q Quiescent Drain Current Vi= 46V, V7= 0V, S1 : B, S2 : B
V6=0V
V
6=3V 66
30 85
40
mA
–I
2L Output Leakage Current Vi= 46V, V6= 3V, S1 : B, S2 : A,
V7=0V 2mA
Note (1) :Using min. 7 A schottky diode.
(2) :Guaranteed by design,not 100 % tested in production.
L296 - L296P
5/21
ELECTRICAL CHARACTERISTICS (continued)
Symbol Parameter Test Conditions Min. Typ. Max. Unit Fig.
SOFT START
I5so Source Current V6= 0V, V5= 3V 80 130 150 µA6b
I
5si Sink Current V6= 3V, V5= 3V 50 70 120 µA6b
INHIBIT
V6L
V6H
Input Voltage
Low Level
High Level
Vi= 9V to 46V, V7= 0V,
S1 : B, S2 : B 0.3
20.8
5.5
V6a
–I
6L
–I
6H
Input Current
with Input Voltage
Low Level
High Level
Vi= 9V to 46V, V7= 0V,
S1 : B, S2 : B
V6= 0.8V
V6=2V 10
3
µA6a
ERROR AMPLIFIER
V9H High Level Output Voltage V10 = 4.7V, I9= 100µA,
S1 : A, S2 : A 3.5 V 6c
V9L Low Level Output Voltage V10 = 5.3V, I9= 100µA,
S1 : A, S2 : E 0.5 V 6c
I9si Sink Output Current V10 = 5.3V, S1 : A, S2 : B 100 150 µA6c
–I
9so Source Output Current V10 = 4.7V, S1 : A, S2 : D 100 150 µA6c
I
10 Input Bias Current V10 = 5.2V, S1 : B
V10 = 6.4V, S1 : B, L296P 2
210
10 µA
µA6c
6c
GvDC Open Loop Gain V9= 1V to 3V, S1 : A, S2 : C 46 55 dB 6c
OSCILLATOR AND PWM COMPARATOR
–I
7Input Bias Current of
PWM Comparator V7= 0.5V to 3.5V 5 µA6a
–I
11 Oscillator Source Current V11 = 2V, S1 : A, S2 : B 5 mA
RESET
V12 R Rising Threshold Voltage Vi= 9V to 46V,
S1 : B, S2 : B
Vref
-150mV Vref
-100mV Vref
-50mV V6d
V
12 F Falling Threshold Voltage 4.75 Vref
-150mV Vref
-100mV V6d
V
13 D Delay Thershold Voltage V12 = 5.3V, S1 : A, S2 : B 4.3 4.5 4.7 V 6d
V13 H Delay Threshold Voltage
Hysteresis 100 mV 6d
V14 S Output Saturation Voltage I14 = 16mA, V12 = 4.7V, S1, S2 : B 0.4 V 6d
I12 Input Bias Current V12 =0VtoV
ref,S1:B,S2:B 1 3 µA6d
–I
13 so
I13 si Delay Source Current
Delay Sink Current
V13 = 3V, S1 : A, S2 : B
V12 = 5.3V
V12 = 4.7V 70
10 110 140 µA
mA
6d
I14 Output Leakage Current Vi= 46V, V12 = 5.3V, S1 : B, S2 : A 100 µA6d
CROWBAR
V1Input Threshold Voltage S1 : B 5.5 6 6.4 V 6b
V15 Output Saturation Voltage Vi= 9V to 46V, Vi= 5.4V,
I15 = 5mA, S1 : A 0.2 0.4 V 6b
I1Input Bias Current V1= 6V, S1 : B 10 µA6b
–I
15 Output Source Current Vi= 9V to 46V, V1= 6.5V,
V15 = 2V, S1 : B 70 100 mA 6b
L296 - L296P
6/21
Figure 4 : DynamicTest Circuit
C7,C8 : EKR(ROE)
L1 : L = 300 µH at8 A Coretype : MAGNETICS58930 - A2 MPP
N°turns :43 Wire Gauge :1 mm (18 AWG) COGEMA 946044
(*) Minimumsuggested value (10 µF) toavoid oscillations. Ripple consideration leads to typical value of 1000 µF or higher.
Figure5 : PC.Board andComponent Layoutof the Circuit of Figure4 (1:1scale)
L296 - L296P
7/21
Figure 6 : DC Test Circuits.
Figure 6a. Figure 6b.
Figure 6c.
Figure 6d.
1 - Set V10 FORV9=1V
2 - Change V10 to obtain V9=3V
3-G
V=DV9=2V
V10 V10
L296 - L296P
8/21
Figure 7 : QuienscentDrain Current vs. Supply
Voltage(0 %Duty Cycle - see fig. 6a). Figure 8 : QuienscentDrain Current vs.Supply
Voltage(100 % Duty Cyclesee fig. 6a).
Figure 9 : QuiescentDrain Current vs. Junction
Temperature (0 % DutyCycle -
seefig.6a).
Figure 10 : QuiescentDrain Current vs. Junction
Temperature(100 % Duty Cycle -
see fig. 6a).
Figure 11 : ReferenceVoltage (pin 10) vs. VI
(seefig. 4). Figure12: ReferenceVoltage(pin 10)vs. Junction
Temperature(see fig. 4).
L296 - L296P
9/21
Figure 13 : OpenLoop FrequencyandPhase
Responseof Error Amplifier
(see fig. 6c).
Figure 14 : Switching Frequency vs. Input
Voltage(see fig.4).
Figure 15 : SwitchingFrequency vs. Junction
Temperature(seefig. 4). Figure 16 : Switching Frequency vs. R1
(see fig. 4).
Figure 17 : LineTransient Response(see fig.4). Figure 18 : Load Transient Response (see fig.4).
L296 - L296P
10/21
Figure 19 : SupplyVoltageRipple Rejectionvs.
Frequency(see fig. 4). Figure 20 : DropoutVoltageBetweenPin3 and
Pin2 vs. Current at Pin 2.
Figure 21 : DropoutVoltageBetweenPin 3 and
Pin 2 vs. Junction Temperature. Figure 22 : Power DissipationDerating Curve.
Figure 23 : PowerDissipation(device only) vs.
Input Voltage. Figure 24 : Power Dissipation(device only)vs.
Inputvoltage.
L296 - L296P
11/21
Figure 25 : PowerDissipation(device only) vs.
OutputVoltage(seefig. 4). Figure 26 : Power Dissipation(device only)vs.
OutputVoltage(see fig. 4).
Figure 28 : Efficiencyvs. OutputCurrent.
Figure 29 : Efficiency vs. OutputVoltage. Figure 30 : Efficiencyvs. OutputVoltage.
Figure27: VoltageandCurrentWaveformsatPin2
(seefig. 4).
L296 - L296P
12/21
Figure 31 : CurrentLimiting Thresholdvs. Rpin 4
(L296Ponly). Figure32: Current LimitingThresholdvs. Junction
Temperature.
Figure 33 : CurrentLimiting Thresholdvs.
SupplyVoltage.
L296 - L296P
13/21
APPLICATION INFORMATION
Figure 34 : TypicalApplicationCircuit.
(*) Minimum value (10 µF) to avoid oscillations ; ripple consideration leadsto typical value of 1000µF orhigher L1 : 58930 - MPP COGEMA
946044 ; GUP 20 COGEMA 946045
SUGGESTED INDUCTOR (L1)
Core Type No Turns Wire Gauge Air Gap
Magnetics 58930 A2MPP 43 1.0 mm
Thomson GUP 20 x 16 x 7 65 0.8 mm 1 mm
Siemens EC 35/17/10 (B6633& G0500 X127) 40 2 x 0.8 mm
VOGT 250 µH Toroidal Coil, Part Number 5730501800
Resistor Values for Standard Output Voltages
V0R8 R7
12 V
15 V
18 V
24 V
4.7 K
4.7 K
4.7 K
4.7 K
6.2 K
9.1 K
12 K
18 K
L296 - L296P
14/21