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Datasheet: L296 (STMicroelectronics)

HIGH CURRENT SWITCHINGREGULATORS

 

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STMicroelectronics
L296
L296P
June 2000
HIGH CURRENT SWITCHING REGULATORS
.
4 A OUTPUT CURRENT
.
5.1 V TO 40 V OUTPUT VOLTAGE RANGE
.
0 TO 100 % DUTY CYCLE RANGE
.
PRECISE (
2 %) ON-CHIP REFERENCE
.
SWITCHING FREQUENCY UP TO 200 KHz
.
VERY HIGH EFFICIENCY (UP TO 90 %)
.
VERY FEW EXTERNAL COMPONENTS
.
SOFT START
.
RESET OUTPUT
.
EXTERNAL PROGRAMMABLE LIMITING
CURRENT (L296P)
.
CONTROL CIRCUIT FOR CROWBAR SCR
.
INPUT FOR REMOTE INHIBIT AND
SYNCHRONUS PWM
.
THERMAL SHUTDOWN
DESCRIPTION
The L296 andL296P are stepdownpower switching
regulators delivering 4 A at a voltage variable from
5.1 V to 40 V.
Featuresof the devices includesoft 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
plasticpower packageand requiresvery 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.
Multi watt
(15 lead)
ORDERING NUMBERS :
L296 (Vertical)
L296HT (Horizontal)
L296P (Vertical)
L296PHT (Horizont al)
PIN CONNECTION (top view)
1/22
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
2/22
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 regulationloop consists of a sawtoothoscillator,
error amplifier, comparatorand the outputstage. An
error signal is produced by comparing the output
voltage with a precise 5.1V on-chipreference(zener
zap trimmed to
2 %). This error signal is then com-
pared with the sawtooth signal to generate the fixed
frequencypulse width modulatedpulseswhich drive
the output stage.The gain and frequencystability of
the loop can be adjusted by an externalRC network
connectedto pin9. Closing the loop directlygives an
outputvoltageof 5.1V.Higher voltagesare 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.
Outputoverloadprotection 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
outputstage 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 externalSCR. This SCR is triggered
when the output voltage exceeds the nominal by
20%. There is no internal connection between the
outputand crowbar sense input thereforethe crow-
bar can monitor either the input or the output.
A TTL - level inhibit input is provided for applications
such as remote on/offcontrol. 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
L296 - L296P
3/22
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
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
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
90
C
20
W
T
j
, T
stg
Junction and Storage Temperature
40 to 150
C
L296 - L296P
4/22
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
3A
9
46
V
4
V
i
Input Voltage Range
Note (1), V
o
= V
REF
to 36V I
o
= 4A
46
V
4
V
o
Line Regulation
V
i
=10V to 40V, V
o
= V
ref
, I
o
= 2A
15
50
mV
4
V
o
Load Regulation
V
o
= V
ref
I
o
= 2A to 4A
I
o
= 0.5A to 4A
10
15
30
45
mV
4
V
ref
Internal Reference Voltage (pin 10) V
i
= 9V to 46V, I
o
= 2A
5
5.1
5.2
V
4
V
ref
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
5
2.5
7
4.5
A
4
I
SH
Input Average Current
V
i
= 46V, Output Short-circuited
60
100
mA
4
Efficiency
I
o
= 3 A
V
o
= V
ref
V
o
= 12V
75
85
%
4
SVR
Supply Voltage Ripple Rejection
V
i
= 2 V
rms
, f
ripple
= 100Hz
V
o
= V
ref
, I
o
= 2A
50
56
dB
4
f
Switching Frequency
85
100
115
kHz
4
f
V
i
Voltage Stability of Switching
Frequency
V
i
= 9V to 46V
0.5
%
4
f
T
j
Temperature Stability of Switching
Frequency
T
j
= 0
C to 125
C
1
%
4
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
66
30
85
40
mA
I
2L
Output Leakage Current
V
i
= 46V, V
6
= 3V, S1 : B, S2 : A,
V
7
= 0V
2
mA
Note
(1) : Using min. 7 A schottky diode.
(2) : Guaranteed by design, not 100 % tested in production.
L296 - L296P
5/22
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