L4978
2A STEP DOWN SWITCHING REGULATOR
1
■
■
Features
UP TO 2A STEP DOWN CONVERTER
OPERATING INPUT VOLTAGE FROM 8V TO
55V
PRECISE 3.3V (±1%) INTERNAL
REFERENCE VOLTAGE
OUTPUT VOLTAGE ADJUSTABLE FROM
3.3V TO 50V
SWITCHING FREQUENCY ADJUSTABLE UP
TO 300KHz
VOLTAGE FEEDFORWARD
ZERO LOAD CURRENT OPERATION
INTERNAL CURRENT LIMITING (PULSE-
BYPULSE AND HICCUP MODE)
INHIBIT FOR ZERO CURRENT
CONSUMPTION
PROTECTION AGAINST FEEDBACK
DISCONNECTION
THERMAL SHUTDOWN
SOFT START FUNCTION
Figure 1. Packages
■
DIP-8
SO16W
■
Table 1. Order Codes
Part Number
L4978
L4978D
L4978D013TR
Package
DIP-8
SO16
SO16 in Tape & Reel
■
■
■
■
■
efficency and high switching speed.
A switching frequency up to 300KHz is achievable
(the maximum power dissipation of the packages
must be observed). A wide input voltage range be-
tween 8V to 55V and output voltages regulated
from 3.3V to 50V cover the majority of today’s ap-
plications. Features of this new generations of DC-
DC converter include pulse-by-pulse current limit,
hiccup mode for short circuit protection, voltage
feedforward regulation, soft-start, protection
against feedback loop disconnection, inhibit for
zero current consumption and thermal shutdown.
The device is available in plastic dual in line, DIP-
8 for standard assembly, and SO16W for SMD as-
sembly.
■
■
■
2
DESCRIPTION
The L4978 is a step down monolithic power
switching regulator delivering 2A at a voltage be-
tween 3.3V and 50V (selected by a simple external
divider). Realized in BCD mixed technology, the
device uses an internal power D-MOS transistor
(with a typical R
dson
of 0.25Ω) to obtain very high
Figure 2. Typical Application Circuit
Vi=8V to 55V
5
R
1
20K
3
C
1
220µF
63V
C
7
220nF
C
2
2.7nF
2
7
8
L4978
4
1
6
L1
126µH
(77120)
D1
ST
PS3L60U
C
8
330µF
V
O
=3.3V/2A
C
5
100nF
R
2
9.1K
C
4
22nF
C
6
100nF
D98IN837A
May 2005
Rev. 9
1/13
STMICROELECTRONICS [ STMICROELECTRONICS ]
