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HIGH CURRENT SWITCHING REGULATORS
L296
L296P
.
4 A OUTPUT CURRENT
HIGH CURRENT SWITCHING REGULATORS
.
5.1 V TO 40 V OUTPUT VOLTAGE RANGE
.
SWITCHING FREQUENCY UP TO 200 KHz
.
VERY HIGH EFFICIENCY (UP TO 90 %)
.
VERY FEW EXTERNAL COMPONENTS
.
SOFT START
.
RESET OUTPUT
.
EXTERNAL PROGRAMMABLE LIMITING
Multiwatt
)
(15 lead)
.
CONTROL CIRCUIT FOR CROWBAR SCR
.
INPUT FOR REMOTE INHIBIT AND
SYNCHRONUS PWM
CURRENT (L296P)
.
THERMAL SHUTDOWN
ORDERING NUMBERS :
L296 (Vertical)
L296HT (Horizontal)
L296P (Vertical)
L296PHT (Horizontal)
DESCRIPTION
The L296 and L296P are stepdown power switching
regulators delivering 4 A at a voltage variable from
5.1 V to 40 V.
Features of the devices include soft start, remote in-
hibit, thermal protection, a reset output for micro-
processors and a PWM comparator input for syn-
chronization in multichip configurations.
The L296P incudes external programmable limiting
current.
The L296 and L296P are mounted in a 15-lead Mul-
tiwatt
)
plastic power package and requires very few
external components.
Efficient operation at switching frequencies up to
200 KHz allows a reduction in the size and cost of
external filter components. A voltage sense input
and SCR drive output are provided for optional
crowbar overvoltage protection with an external
SCR.
PIN CONNECTION
(top view)
April 1993
1/21
.
0 TO 100 % DUTY CYCLE RANGE
.
PRECISE (
±
2 %) ON-CHIP REFERENCE
L296 - L296P
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
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.
FREQUENCY
COMPENSATION
BLOCK DIAGRAM
2/21
9
L296 - L296P
CIRCUIT OPERATION
(refer to the block diagram)
The L296 and L296P are monolithic stepdown
switching regulators providing output voltages from
5.1V to 40V and delivering 4A.
The regulation loop consists of a sawtooth oscillator,
error amplifier, comparator and the output stage. An
error signal is produced by comparing the output
voltage with a precise 5.1V on-chip reference (zener
zap trimmed to
±
2 %). This error signal is then com-
pared with the sawtooth signal to generate the fixed
frequencypulse width modulatedpulses which drive
the output stage. The gain and frequency stability of
the loop can be adjusted by an external RC network
connectedto pin 9. Closing the loop directly gives an
output voltage of 5.1V. Higher voltages are obtained
by inserting a voltage divider.
Output overcurrents at switch on are prevented by
the soft start function. The error amplifier output is
initially clamped by the external capacitor Css and
allowed to rise, linearly, as this capacitor is charged
by a constant current source.
Output overload protection is provided in the form of
a current limiter. The load current is sensed by an
internal metal resistor connected to a comparator.
When the load current exceeds a preset threshold
this comparator sets a flip flop which disables the
output stage and discharges the soft start capacitor.
A second comparator resets the flip flop when the
voltage across the soft start capacitor has 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 overload condition is still present the
limiter will trigger again when the threshold current
is reached. The average short circuit current is lim-
ited to a safe value by the dead time introduced by
the soft start network.
The reset circuit generates an output signal when
the supply voltage exceeds a threshold pro-
grammed by an external divider. The reset signal is
generated with a delay time programmed by an ex-
ternal capacitor. When the supply falls below the
threshold the reset output goes low immediately.
The reset output is an open collector.
The scrowbar circuit senses the output voltage and
the crowbar output can provide a current of 100mA
to switch on an external SCR. This SCR is triggered
when the output voltage exceeds the nominal by
20%. There is no internal connection between the
output and crowbar sense input therefore the crow-
bar can monitor either the input or the output.
A TTL - level inhibit input is provided for applications
such as remote on/off control. This input is activated
by high logic level and disables circuit operation. Af-
ter an inhibit the L296 restarts under control of the
soft start network.
The thermal overload circuit disables circuit opera-
tion when the junction temperature reaches about
150
°
C and has hysteresis to prevent unstable con-
ditions.
Figure 1 :
Reset Output Waveforms
3/21
L296 - L296P
Figure 2 :
Soft Start Waveforms
Figure 3 :
Current Limiter Waveforms
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Value
Unit
V
i
Input Voltage (pin 3)
50
V
V
i
–V
2
Input to Output Voltage Difference
50
V
V
2
Output DC Voltage
Output Peak Voltage at t = 0.1
m
sec f = 200KHz
–1
–7
V
V
V
1
,V
12
Voltage at Pins 1, 12
10
V
V
15
Voltage at Pin 15
15
V
V
4
,V
5
,V
7
,V
9
,V
13
Voltage at Pins 4, 5, 7, 9 and 13
5.5
V
V
10
,V
6
Voltage at Pins 10 and 6
7
V
V
14
Voltage at Pin 14 (I
14
3
1 mA)
V
i
I
9
Pin 9 Sink Current
1
mA
I
11
Pin 11 Source Current
20
mA
I
14
Pin 14 Sink Current (V
14
< 5 V)
50
mA
P
tot
Power Dissipation at T
case
3
90
°
C
20
W
T
j
,T
stg
Junction and Storage Temperature
– 40 to 150
°
C
4/21
L296 - L296P
THERMAL DATA
Symbol
Parameter
Value
Unit
R
th j-case
Thermal Resistance Junction-case
Max.
3
°
C/W
R
th j-amb
Thermal Resistance Junction-ambient
Max.
35
°
C/W
ELECTRICAL CHARACTERISTICS
(refer to the test circuits T
j
=25
o
C, V
i
= 35V, unless otherwise specified)
Symbol
Parameter
Test Conditions
Min. Typ. Max. Unit Fig.
DYNAMIC CHARACTERISTICS (pin 6 to GND unless otherwise specified)
V
o
Output Voltage Range
V
i
= 46V, I
o
=1A
V
ref
40
V
4
V
i
Input Voltage Range
V
o
=V
ref
to 36V, I
o
3
3A
9
46
V
4
V
i
Input Voltage Range
Note (1), V
o
=V
REF
to 36V I
o
=4A
46
V
4
D
V
o
Line Regulation
V
i
=10V to 40V, V
o
=V
ref
,I
o
=2A
15 50
mV
4
D
V
o
Load Regulation
V
o
=V
ref
I
o
=2Ato4A
I
o
= 0.5A to 4A
mV
4
10
15
30
45
V
ref
Internal Reference Voltage (pin 10) V
i
= 9V to 46V, I
o
= 2A
5
5.1 5.2
V
4
D
V
ref
D
T
Average Temperature Coefficient
of Reference Voltage
T
j
=0
°
C to 125
°
C, I
o
= 2A
0.4
mV/
°
C
V
d
Dropout Voltage Between Pin 2
and Pin 3
I
o
=4A
I
o
=2A
2
1.3
3.2
2.1
V
V
4
4
I
2L
Current Limiting Threshold (pin 2) L296 - Pin 4 Open,
V
i
= 9V to 40V, V
o
=V
ref
to 36V
4.5
7.5
A
4
L296P - V
i
= 9V to 40V, V
o
=V
ref
Pin 4 Open
R
Iim
= 22k
A4
5
2.5
7
4.5
W
I
SH
Input Average Current
V
i
= 46V, Output Short-circuited
60
100
mA
4
h
Efficiency
I
o
=3A
V
o
=V
ref
V
o
= 12V
75
85
%4
SVR
Supply Voltage Ripple Rejection
V
i
=2V
rms
,f
ripple
= 100Hz
V
o
=V
ref
,I
o
=2A
50
56
dB
4
f
Switching Frequency
85 100 115
kHz
4
D
f
Voltage Stability of Switching
Frequency
V
i
= 9V to 46V
0.5
%
4
D
V
i
D
f
Temperature Stability of Switching
Frequency
T
j
=0
°
C to 125
°
C
1
%
4
D
T
j
f
max
Maximum Operating Switching
Frequency
V
o
=V
ref
,I
o
= 1A
200
kHz
–
T
sd
Thermal Shutdown Junction
Temperature
Note (2)
135 145
C–
DC CHARACTERISTICS
I
3Q
Quiescent Drain Current
V
i
= 46V, V
7
= 0V, S1 : B, S2 : B
V
6
=0V
V
6
=3V
mA
66
30
85
40
–I
2L
Output Leakage Current
V
i
= 46V, V
6
= 3V, S1 : B, S2 : A,
V
7
=0V
2A
Note
(1) : Using min. 7 A schottky diode.
(2) : Guaranteed by design, not 100 % tested in production.
5/21
D
°
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