L4960
2.5A POWER SWITCHING REGULATOR
2.5A OUTPUT CURRENT
5.1V TO 40V OPUTPUT VOLTAGE RANGE
PRECISE (
2%) ON-CHIP REFERENCE
HIGH SWITCHING FREQUENCY
VERY HIGH EFFICIENCY (UP TO 90%)
VERY FEW EXTERNAL COMPONENTS
SOFT START
INTERNAL LIMITING CURRENT
THERMAL SHUTDOWN
DESCRIPTION
The L4960 is a monolithic power switching regula-
tor delivering 2.5A at a voltage variable from 5V to
40V in step down configuration.
Features of the device include current limiting, soft
start, thermal protection and 0 to 100% duty cycle
for continuous operation mode.
June 2000
ORDERING NUMBERS: L4960 (Vertical)
L4960H (Horizontal)
HEPTAWATT
BLOCK DIAGRAM
The L4960 is mounted in a Heptawattplastic power
package and requires very few external compo-
nents.
Efficient operation at switching frequencies up to
150KHz allows a reduction in the size and cost of
external filter components.
1/16
PIN CONNECTION (Top view)
2/16
N
NAME
FUNCTION
1
SUPPLY VOLTAGE
Unregulated voltage input. An internal regulator powers the
internal logic.
2
FEEDBACK INPUT
The feedback terminal of the regulation loop. The output is
connected directly to this terminal for 5.1V operation; it is
connected via a divider for higher voltages.
3
FREQUENCY
COMPENSATION
A series RC network connected between this terminal and
ground determines the regulation loop gain characteristics.
4
GROUND
Common ground terminal.
5
OSCILLATOR
A parallel RC network connected to this terminal determines the
switching frequency.
6
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.
7
OUTPUT
Regulator output.
PIN FUNCTIONS
Symbol
Parameter
Value
Unit
V
1
Input voltage
50
V
V
1
- V
7
Input to output voltage difference
50
V
V
7
Negative output DC voltage
-1
V
Negative output peak voltage at t = 0.1
s; f = 100KHz
-5
V
V
3
, V
6
Voltage at pin 3 and 6
5.5
V
V
2
Voltage at pin 2
7
V
I
3
Pin 3 sink current
1
mA
I
5
Pin 5 source current
20
mA
P
to t
Power dissipation at T
case
90
C
15
W
T
j
, T
stg
Junction and storage temperature
-40 to 150
C
ABSOLUTE MAXIMUM RATINGS
L4960
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
DYNAMIC CHARACTERISTICS
V
o
Output voltage range
V
i
= 46V
I
o
= 1A
V
ref
40
V
V
i
Input voltage range
V
o
= V
ref
to 36V
I
o
= 2.5A
9
46
V
V
o
Line regulation
V
i
= 10V to 40V
V
o
= V
ref
I
o
= 1A
15
50
mV
V
o
Load regulation
V
o
= V
ref
I
o
= 0.5A to 2A
10
30
mV
V
ref
Internal reference voltage
(pin 2)
V
i
= 9V to 46V
I
o
= 1A
5
5.1
5.2
V
V
ref
T
Average temperature
coefficient of refer voltage
T
j
= 0
C to 125
C
I
o
= 1A
0.4
mV/
C
V
d
Dropout voltage
I
o
= 2A
1.4
3
V
I
om
Maximum operating load
current
V
i
= 9V to 46V
V
o
= V
ref
to 36V
2.5
A
I
7L
Current limiting threshold
(pin 7)
V
i
= 9V to 46V
V
o
= V
ref
to 36V
3
4.5
A
I
SH
Input average current
V
i
= 46V;
output short-circuit
30
60
mA
Efficiency
f = 100KHz
V
o
= V
ref
75
%
I
o
= 2A
V
o
= 12V
85
%
SVR
Supply voltage ripple
rejection
V
i
= 2V
rms
fripple
= 100Hz
V
o
= V
ref
Io = 1A
50
56
dB
f
Switching frequency
85
100
115
KHz
f
V
i
Voltage stability of
switching frequency
V
i
= 9V to 46V
0.5
%
f
T
j
Temperature stability of
switching frequency
T
j
= 0
C to 125
C
1
%
f
max
Maximum operating
switching frequency
V
o
= V
ref
I
o
= 2A
120
150
KHz
T
sd
Thermal shutdown
junction temperature
150
C
ELECTRICAL CHARACTERISTICS (Refer to the test circuit, T
j
= 25
C, V
i
= 35V, unless otherwise
specified)
Symbol
Parameter
Value
Unit
R
th j-case
Thermal resistance junction-case
max
4
C/W
R
th j-amb
Thermal resistance junction-ambient
max
50
C/W
THERMAL DATA
3/16
L4960
4/16
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
DC CHARACTERISTICS
I
1Q
Quiescent drain current
100% duty cycle
pins 5 and 7 open
V
i
= 46V
30
40
mA
0% duty cycle
15
20
mA
-I
7L
Output leakage current
0% duty cycle
1
mA
SOFT START
I
6SO
Source current
100
140
180
A
I
6SI
Sink current
50
70
120
A
ERROR AMPLIFIER
V
3H
High level output voltage
V
2
= 4.7V
I
3
= 100
A
3.5
V
V
3L
Low level output voltage
V
2
= 5.3V
I
3
= 100
A
0.5
V
I
3SI
Sink output current
V
2
= 5.3V
100
150
A
-I
3SO
Source output current
V
2
= 4.7V
100
150
A
I
2
Input bias current
V
2
= 5.2V
2
10
A
G
v
DC open loop gain
V
3
= 1V to 3V
46
55
dB
OSCILLATOR
-I
5
Oscillator source current
5
mA
ELECTRICAL CHARACTERISTICS (continued)
L4960
CIRCUIT OPERATION (refer to the block diagram)
The L4960 is a monolithic stepdownswitching regu-
lator providing output voltagesfrom 5.1V to 40V and
delivering 2.5A.
The regulation loop consists of a sawtooth oscilla-
tor, error amplifier, comparator and the output
stage. An error signal is produced by comparing the
output voltage with a precise 5.1V on-chip refer-
ence (zener zap trimmed to
2%).
This error signal is thencompared with the sawtooth
signal to generate the fixed frequency pulse width
modulated pulses which drive the output stage.
The gain and frequency stability of the loop can be
adjusted by an external RC network connected to
pin 3. 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 C
ss
and
allowed to rise, linearly, as this capacitor is charged
by a constant current source. Output overload pro-
tection 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 com-
parator 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 limited
to a safe value by the dead time introduced by the
soft start network. The thermal overload circuit dis-
ables circuit operation when the junction tempera-
ture reaches about 150
C and has hysteresis to
prevent unstable conditions.
Figure 1. Soft start waveforms
Figure 2. Current limiter waveforms
5/16
L4960
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