L4978_05 Datasheet, PDF (1/13 Pages) STMicroelectronics – 2A STEP DOWN SWITCHING REGULATOR

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
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 1. Packages
DIP-8
Table 1. Order Codes
Part Number
L4978
L4978D
L4978D013TR
SO16W
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.
Figure 2. Typical Application Circuit
Vi=8V to 55V
C₁
220µF
63V
C₇
220nF
R₁
20K
C₂
2.7nF
C₅
100nF
5
8
L4978
3
4
2
7
16
L1
126µH
(77120)
V_O=3.3V/2A
R₂
9.1K
C₄
22nF
C₆
100nF
D1
ST
PS3L60U
C₈
330µF
May 2005
D98IN837A
Rev. 9
1/13