
February 2009
Rev 18
1/28
28
L4973
3.5 A step down switching regulator
Features
■ Up to 3.5 A step down converter
■ Operating input voltage from 8 V to 55 V
■ 3.3 V and 5.1 V (±1%) fixed output, and
adjustable outputs from:
– 0.5 V to 50 V (3.3 type)
– 5.1 V to 50 V (5.1 type)
■ Frequency adjustable up to 300 kHz
■ Voltage feed forward
■ Zero load current operation (min. 1 mA)
■ Internal current limiting (pulse by pulse and
HICCUP mode)
■ Precise 5.1 V (1.5%) reference voltage
externally available
■ Input/output synchronization function
■ Inhibit for zero current consumption (100 mA
typ. at VCC = 24 V)
■ Protection against feedback disconnection
■ Thermal shutdown
■ Output over voltage protection
■ Soft-start function
Description
The L4973 is a step down monolithic power
switching regulator delivering 3.5 A at fixed
voltages of 3.3 V or 5.1 V and using a simple
external divider output adjustable voltage up to
50V. Realized in BCD mixed technology, the
device uses an internal power D-MOS transistor
(with a typical RDS(on) of 0.15 Ω) to obtain very
high efficiency and very fast switching times.
Switching frequency up to 300 kHz are achievable
(the maximum power dissipation of the packages
must be observed).
A wide input voltage range between 8 V to 55 V
and output voltages regulated from 3.3 V to 40 V
cover the majority of the today applications.
Features of this new generation of DC-DC
converter includes pulse by pulse current limit,
hiccup mode for output short circuit protection,
voltage feed forward regulation, soft-start,
input/output synchronization, protection against
feedback loop disconnection, inhibit for zero
current consumption and thermal shutdown.
Packages available are in plastic dual in line, DIP-
18 (12+3+3) for standard assembly, and SO20
(12+4+4) for SMD assembly.
DIP-18 (12+3+3)
SO-20 (12+4+4)
Figure 1.
Internal schematic diagram
L4973
V
CC (8V to 55V)
CIN
C2
ROSC
COSC
D1
L1
COUT
VO(3.3V or 5.1V)
CBOOT
4,5,6,10
13,14,15
7
9
8
1
11
3
D97IN554A
17
RCOMP
CCOMP
CSS
2
16
12