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L4963-L4963D013TR
1.5A SWITCHING REGULATOR
L4963
L4963D1.5A SWITCHING REGULA TOR
1.5A OUTPUT LOAD CURRENT
5.1 TO 36V OUTPUT VOLTAGE RANGE
DISCONTINUOUS VARIABLE FREQUENCY
MODE
PRECISE (+/–2%) ON CHIP REFERENCE
VERY HIGH EFFICIENCY
VERY FEW EXTERNAL COMPONENTS
NO FREQ. COMPENSATION REQUIRED
RESET AND POWER FAIL OUTPUT FOR MI-
CROPROCESSOR
INTERNAL CURRENT LIMITING
THERMAL SHUTDOWN
DESCRIPTIONThe L4963 is a monolithic power switching regulator
delivering 1.5A at 5.1V. The output voltage is adjust-
able from 5.1V to 36V , working in discontinuous
variable frequency mode. Features of the device
include remote inhibit, internal current limiting and
thermal protection, reset and power fail outputs for
microprocessor.
BLOCK DIAGRAMThe L4963 is mounted in a 12+3+3 lead Powerdip
(L4963) and SO20 large (L4963D) plastic pack-
ages and requires very few external components.
June 2000 1/17
ABSOLUTE MAXIMUM RATINGS
PIN CONNECTION (top view)
L4963 - L4963D
PIN FUNCTIONS
THERMAL DATA(*) See Fig. 28
L4963 - L4963D3/17
CIRCUIT DESCRIPTION (Refer to Block Dia-
gram)The L4963 is a monolithic stepdown regulator pro-
viding 1.5A at 5.1V working in discontinuous vari-
able frequency mode. In normal operation the
device resonates at a frequency depending primar-
ily on the inductance value, the input and output
voltage and the load current. The maximum switch-
ing however can be limited by an internal oscillator,
which can be programmed by only one external
resistor.
The fondamental regulation loop consists of two
comparators, a precision 5.1V on-chip reference
and a drive latch. Briefly the operation is as follows:
when the choke ends its discharge the catch free-
wheeling recirculation filter diode begins to come
out of forward conduction so the output voltage of
the device approaches ground. When the output
voltage reaches –0.1V the internal comparator sets
the latch and the power stage is turned on. Then
the inductor current rises linearly until the voltage
sensed at the feedback input reaches the 5.1V
reference.
The second comparator then resets the latch and
the output stage is turned off. The current in the
choke falls linearly until it is fully discharged, then
the cycle repeats. Closing the loop directly gives an
output voltage of 5.1V. Higher output voltages are
obtained by inserting a voltage divider and this
method of control requires no frequency compen-
sation network. At output voltages greater than
5.1V the available output current must be derated
due to the increased power dissipation of the de-
vice.
Output overload protection is provided by an inter-
nal current limiter. The load current is sensed by a
on-chip metal resistor connected to a comparator
which resets the latch and turns off the power stage
in overload condition. The reset circuits (see fig. 1)
generates an output high signal when the output
voltage value is correct. It has an open collector
output and the output signal delay time can be
programmed with an external capacitor. A power-
fail circuit is also available and is used to monitor
the supply voltage. Its output goes high when the
supply voltage reaches a pre-programmed treshold
set by a voltage divider to its input from the supply
to ground. With the input left open the threshold is
approximately equal to 5.1V. The output of the
power fail is an open collector.
A TTL level inhibit is provided for applications such
as remote on/off control. This input is activated by
a low logic level and disables circuits operation.
The thermal overload circuit disables the device
when the junction temperature is about 150°C and
has hysteresis to prevent unstable conditions.
Figure 1: Reset and Power Fail Function
L4963 - L4963D
ELECTRICAL CHARACTERISTIC (Refer to the test circuit Vi = 30V Tj = 25°C unless otherwise specified )
DYNAMIC CHARACTERISTICS
DC CHARACTERISTICS
INHIBIT
L4963 - L4963D5/17
