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L4978-L4978D
2A STEP DOWN SWITCHING REGULATOR
gerTpra'
2A STEP DOWN SWITCHING REGULATOR
UP TO 2A STEP DOWN CONVERTER
OPERATING INPUT VOLTAGE FROM 8V TO
n PRECISE 3.3V (i1%) INTERNAL REFER-
ENCE VOLTAGE
n OUTPUT VOLTAGE ADJUSTABLE FROM
3.3V TO 50V
n SWITCHING FREQUENCY ADJUSTABLE UP
TO 300KHZ
n VOLTAGE FEEDFORWARD
n ZERO LOAD CURRENT OPERATION
n INTERNAL CURRENT LIMITING (PULSE-BY-
PULSE AND HICCUP MODE)
.1 INHIBIT FOR ZERO CURRENT CONSUMP-
n PROTECTION AGAINST FEEDBACK DIS-
CONNECTION
n THERMAL SHUTDOWN
n SOFT START FUNCTION
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 exter-
nal divider). Realized in BCD mixed technology,
the device uses an internal power D-MOS transis-
tor (with a typical Rdson of 0.259) to obtain very
high eNcency and high switching speed.
TYPICAL APPLICATION CIRCUIT
'iiiiiiii)ti;;;;;i)r,
Minidip SO16W
ORDERING NUMBERS: L4978 (Minidip)
L4978D (SO16)
A switching frequency up to 300KHz is achiev-
able (the maximum power dissipation of the pack-
ages must be observed).
A wide input voltage range between 8V to 55V
and output voltages regulated from 3.3V to 50V
cover the majority of today's applications.
Features of this new generations of DC-DC con-
verter include pulse-by-pulse current limit, hiccup
mode for short circuit protection, voltage feedfor-
ward regulation, soft-start, protection against
feedback loop disconnection, inhibit for zero cur-
rent consumption and thermal shutdown.
The device is available in plastic dual in line,
MINIDIP 8 for standard assembly, and SO16W
for SMD assembly.
Vi=8Vto 55V
7 1 6 LI V =3.3V/2A
220 A A A 126pH C)
63V " I I (77120)
Ce '==,
R2 100nF --
9.1K Ca
T 22nF
DQBIN83 TA
October 2001
BLOCK DIAGRAM
THERMAL - VOLTAGES I
SHUTDOWN MONITOR
I CBOOT
CHARGE
2 INTERNAL INTERNAL
SS_INH _ INHIBIT - SOFTSTART o- REFERENCE - SUPPLY Tfl, l
3.3V .
COMP 7 - - e
FB PWM R
o - CBOOT
3.3V l" S :} CHARGE
DRIVE AT LIGHT
OSCILLATOR I
l 3 l 4
OSC GND OUT D97iN594
PIN CONNECTIONS
N.C. CI: 1 16 D N.C.
GND U: 2 15 CIC) N.C.
V INH 14 FB
GND E 1 8 Cl F B ss, g 3 g
OSC 4 13 COMP
SS_INH E 2 7 Cl COMP OUT CE 5 12 D BOOT
OSC l: 3 6 Cl BOOT
OUT I: 4 5 Cl VCC OUT Cl: 6 11 CIC) VCC
N.C. CE 7 10 ID NO.
D97IN595 N.C. UE 8 9 CIC) NC.
D97IN596
Minidip SO16W
PIN FUNCTIONS
DIP SO (*) Name Function
1 2 GND Ground
2 3 SS_INH A logic signal (active low) disables the device (sleep mode operation).
A capacitor connected between this pin and ground determines the soit start time.
When this pin is grounded disables the device (driven by open collector/drain).
3 4 OSC An external resistor connected between the unregulated input voltage and this pin and
a capacitor connected from this pin to ground fix the switching frequency. (Line feed
forward is automatically obtained)
4 5, 6 OUT Stepdown regulator output
5 11 Vcc Unregulated DC input voltage
6 12 BOOT A capacitor connected between this pin and OUT allows to drive the internal DMOS
Transistors
7 13 COMP E/A output to be used for frequency compensation
8 14 FB Stepdown feedback input. Connecting directly to this pin results in an output voltage of
3.3V. An external resistive divider is required for higher output voltages.
(*) Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die.
2/12 £77
