STLD20D Datasheet, PDF (1/8 Pages) STMicroelectronics – WHITE LED POWER SUPPLY

®
STLD20D
ASD™
FEATURES
■ High efficiency above 80%
■ Can drive up to 4 LEDs in series from 2.8V
supply
■ Constant LED current regulation
■ Integrated LED disconnect switch that cuts the
LEDs branch in shutdown mode
■ Constant switching frequency
■ Stable current regulation across the total input
voltage range
■ Supply voltage rejection
■ Inherent soft start by limiting the peak inductor
current
■ Peak inductor current adjustability (STLD20D-
C8 only)
■ Shutdown pin with possibility of PWM dimming
control
■ Over voltage and over temperature protection
with automatic restart
■ Low shutdown current < 1µA
■ Small external inductor (10µH, height < 2mm)
■ Tiny ceramic external capacitor
■ Can be supplied by a Li-ion battery - V_IN range:
2.5Vdc to 5Vdc
WHITE LED POWER SUPPLY
PRELIMINARY DATA
APPLICATION
■ White Led supply for LCD backlight
■ Mobile phone
■ PDA and organizers
■ Any handsets powered from 2.8V to 4.2V
DESCRIPTION
The STLD20D is a constant switching frequency
boost regulator with specific features to supply up
to 4 white LEDs in series. A stable LED current
regulation, from 2.8V to 4.2V, is achieved by sens-
ing the LED current through a low ohmic shunt re-
sistor R_LED (see figure 1). The device also
includes a supply rejection circuit that prevent any
kind of flickering effect on the display during dy-
namic supply voltage variation. A LED disconnect
switch cut the LED branch to reduce the current
consumption in shutdown mode. The maximum
peak inductor current can be programmed. The
STLD20D includes often numerous features and in-
novative design circuit that allows getting an efficien-
cy above 80% across the total supply voltage range.
Figure 1: Basic connection
L = 10µH
D
VBATT
Cin = 2.2µF
Cout = 1µF
SW
VOUT
RSET (*)
RSET
VIN
STLD20D
LDS
ILED = 20mA
SHDN
GND
(*) STLD20D-C8 only
FB
D: STM BAT20J
RLED
L: Murata LQH32CN100K33
Table 1: Order Codes
Part Number
STLD20D-C8
STLD20D-DEF
Marking
L2D
L2D
Package
SOT23-8L
QFN 3x3 8L
Figure 2: Efficiency versus input voltage
(I_LED=20mA; T_amb=25°C)
Efficiency (%)
88
87
86
85
84
83
82
81
80
79
78
2.5
3
3.5
4
4.5
5
Input voltage (Vdc)
October 2004
REV. 2
1/8
This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice.