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L4960H
2.5A POWER SWITCHING REGULATOR
L49602.5A 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
DESCRIPTIONThe 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
BLOCK DIAGRAMThe L4960 is mounted in a Heptawatt plastic 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
PIN FUNCTIONS
ABSOLUTE MAXIMUM RATINGS
L4960
DYNAMIC CHARACTERISTICS
ELECTRICAL CHARACTERISTICS (Refer to the test circuit, Tj = 25 °C, Vi = 35V, unless otherwise
specified)
THERMAL DATA3/16
L4960
4/16
DC CHARACTERISTICS
SOFT START
ERROR AMPLIFIER
OSCILLATOR
ELECTRICAL CHARACTERISTICS (continued)
L4960
CIRCUIT OPERATION (refer to the block diagram)The L4960 is a monolithic stepdown switching regu-
lator providing output voltages from 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 then compared 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 Css 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 waveforms5/16
L4960
6/16
Figure 4. Quiescent drain
current vs. supply voltage (0%
duty cycle)
Figure 5. Quiescent drain
current vs. supply voltage
(100% duty cycle)
Figure 6. Quiescent drain
current vs. junction tem-
perature (0% duty cycle)
Figure 3. Test and application circuit
L4960
Figure 7. Quiescent drain
current vs. junction tem-
perature (100% duty cycle)
Figure 8. Reference voltage
(pin 2) vs. Vi
Figure 9. Reference voltage
versus junction temperature
(pin 2)
Figure 10. Open loop fre-
quency and phase responde
of error amplifier
Figure 11. Switching fre-
quency vs. input voltage
Figure 12. Switching fre-
quency vs. junction tem-
perature
Figure 13. Switching fre-
quency vs. R2 (see test circuit)
Figure 14. Line transient
response Figure 15. Load transient
response7/16
L4960
8/16
Figure 16. Supply voltage
ripple rejection vs. frequency
Figure 17. Dropout voltage
between pin 1 and pin 7 vs.
current at pin 7
Figure 18. Dropout voltage
between pin 1 and 7 vs.
junction temperature
Figure 19. Power dissipation
derating curve Figure 20. Efficiency vs.
output current
Figure 21. Efficiency vs.
output current
Figure 22. Efficiency vs.
output current
Figure 23. Efficiency vs.
output voltage
L4960
