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HIGH CURRENT SWITCHING REGULATOR
L4964
HIGH CURRENT SWITCHING REGULATOR
.
4 A OUTPUT CURRENT
.
5.1 V TO 28 V OUTPUT VOLTAGE RANGE
.
SWITCHING FREQUENCY UP TO 120 KHz
.
VERY HIGH EFFICIENCY (UP TO 90 %)
.
VERY FEW EXTERNAL COMPONENTS
.
SOFT START
.
RESET OUTPUT
.
CURRENT LIMITING
.
INPUT FOR REMOTE INHIBIT AND SYN-
CHRONUS PWM
MUL TIW AT T15 Verti cal
(Plastic Package)
.
THERMAL SHUTDOWN
ORDERING NUMBER : L4964
DESCRIPTION
The L4964 is a stepdown power switching regulator
delivering 4A at a voltage variable from 5.1V to 28V.
Features of the device include overload protection,
soft start, remote inhibit, thermal protection, a reset
output for microprocessors and a PWM comparator
input for synchronization in multichip configurations.
The L4964 is mounted in a 15-lead Multiwatt
)
plas-
tic power package and requires very few external
components.
Efficient operation at switching frequencies up to
120kHz allows a reduction in the size and cost of ex-
ternal filter components.
MULTIWATT15 Horizontal
(Plastic Package)
ORDERING NUMBER : L4964HT
PIN CONNECTION
(top view)
Pins 1, 4, 15 must not be connected. Leave open circuit.
April 1993
1/13
.
0 TO 100 % DUTY CYCLE RANGE
.
PRECISE (
±
3 %) ON-CHIP REFERENCE
L4964
PIN FUNCTIONS
N
°
Name
Function
1
N.C.
Must not be connected. Leave open circuit.
2
Output
Regulator Output.
3
Supply Voltage
Unregulated Voltage Input. An internal regulator powers the L4964’s internal logic.
4
N.C.
Must not be connected. Leave open circuit.
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 L4964.
7
Sync Input
Multiple L4964’s 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 of the Regulation Loop. The output is connected directly to
this terminal for 5.1 V operation ; it is connected via a divider for higher voltages.
11
Oscillator
A parallel RC network connected to this terminal determines the switching frequency.
The 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
beedback 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
N.C.
Must not be connected. Leave open circuit.
BLOCK DIAGRAM
2/13
L4964
CIRCUIT OPERATION
(refer to the block diagram)
The L4964 is a monolithic stepdown switching regu-
lator providing output voltages from 5.1 V to 28 V
and delivering 4A.
The regulation loop consists of asawtooth oscillator,
error amplifier, comparator and the output stage. An
error signal is produced by comparing the output
voltage with a precise 5.1 V on-chip reference
(zener zap trimmed to
±
3 %). This error signal is
then compared with the sawtooth signal to generate
the fixed frequency pulse width modulated pulses
which drive the output stage. The gain and fre-
quency stability of the loop can be ajusted by an ex-
ternal RC network connected to pin 9. Closing the
loop directly gives an output voltage of 5.1 V. 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 C
ss
and al-
lowed 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
0.4 V. The output stage is thus re-enable and the
outputvoltage rises undercontro of the soft startnet-
work. If the overload condition is still present the
limiter will trigger again when the thershold 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.
A TTL - level input is provided for applications such
as remote on/off control. This input is activated by
high level and disables circuit operation. After an in-
hibit the L4964 restarts under control of the soft start
network.
The thermal overload circuit disables circuit opera-
tion when the junction temperature reaches about
150 and has hysteresis to prevent unstable condi-
tions.
Figure 1 :
Reset Output Waveforms
3/13
L4964
Figure 2 :
Soft Start Waveforms
Figure 3 :
Current Limiter Waveforms
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Value
Unit
V
i
Input Voltage (pin 3)
36
V
V
i
–V
2
Input to Output Voltage Difference
38
V
V
2
Output DC Voltage
Output Peak Voltage at t = 0.1
m
sec f = 100 kHz
–1
–7
V
V
V
12
Voltage at Pin 12
10
V
V
5
,V
7
,V
9
Voltage at Pins 5, 7 and 9
5.5
V
V
10
,V
6
,V
13
Voltage at Pins 10, 6 and 13
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
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
4/13
L4964
ELECTRICAL CHARACTERISTICS
(refer to the test circuits T
j
=25
o
C, V
i
= 25V, 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
= 36V, I
o
=1A
V
ref
28
V
4
V
i
Input Voltage Range
V
o
=V
ref
to 28V, I
o
=3A
9
36
V
4
D
V
o
Line Regulation
V
i
= 10V to 30V, V
o
=V
ref
,I
o
=2A
15 70
mV
4
D
V
o
Load Regulation
I
o
=1Ato2A
I
o
= 0.5A to 3A, V
o
=V
ref
10
15
30
50
mV
mV
4
4
V
ref
Internal Reference Voltage (Pin 10) V
i
= 9V to 36V, I
o
= 2A
4.95 5.1 5.25
V
4
D
V
ref
D
Average Temperature Coefficient
of Reference Voltage
T
j
=0
°
C to 125
°
C, I
o
= 2A
0.4
mV/
°
C
T
V
d
Dropout Voltage between Pin 2
and Pin 3
I
o
=3A
I
o
=2A
2
1.5
3.2
2.4
V
V
4
4
Io
m
Maximum Operating Load Current V
I
= 9V to 36V, V
o
=V
ref
to 28V
4
A
4
I
2L
Current Limiting Threshold (Pin 2) V
i
= 9V to 36V, V
o
=V
re
f to 28V
4.5
8
A
4
I
SH
Input Average Current
V
i
= 36V, Output Short-circuited
80
140
mA
4
h
Efficiency
I
o
=3A
V
o
=V
ref
V
o
= 12V
75
85
%
%
4
4
SVR
Supply Voltage Ripple Rejection
V
I
=2V
rms
,f
ripple
= 100Hz
V
o
=V
ref
,I
o
=2A
46
56
–
dB
4
f
Switching Frequency
40
50
60
kHz
4
D
f
Voltage Stability of Switching
Frequency
V
i
= 9V to 36V
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
120
kHz
–
T
sd
Thermal Shutdown Junction
Temperature
135 145
°
C–
DC CHARACTERISTICS
I
3Q
Quiescent Drain Current
V
i
= 36V, V
7
= 0V, S1 : B, S2 : B
V
6
=0V
V
6
=3V
mA
6a
66
30
100
50
–I
2L
Output Leakage Current
V
i
= 36V, V
6
= 3 V, V
7
=0V
S1 : B, S2 : A
2
A6a
SOFT START
I
5so
Source Current
V
6
= 0V, V
5
= 3V
80 130 180
m
Ab
I
5si
Sink Current
V
6
= 3V, V
5
= 3V
40
70
140
m
Ab
INHIBIT
V
6L
Low Input Voltage
V
i
= 9V to 36V, V
7
=0V
S1 : B, S2 : B
- 0.3
0.8
V
6a
V
6H
High Input Voltage
2
5.5
V
6a
Input Current with Input Voltage
V
i
= 9V to 36V, V
7
=0V
S1 : B, S2 : B
V
6
= 0.8V
V
6
=2V
m
Aa
–I
6L
–I
6H
Low Level
High Level
20
10
ERROR AMPLIFIER
V
9H
High Level Output Voltage
V
10
= 4.7V, I
9
= 100
m
A, S1 : A,
3.4
V
6c
S2 : A
V
9L
Low Level Output Voltage
V
10
= 5.3V, I
9
= 100
m
A, S1 : A,
0.6
V
6c
S2 : E
I
9si
Sink Output Current
V
10
= 5.3V, S1 : A, S2 : B
100 150
m
Ac
–I
9so
Source Output Current
V
10
= 4.7V, S1 : A, S2 : D
100 150
m
Ac
5/13
D
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