LTC3452 Datasheet, PDF (1/16 Pages) Linear Technology – Synchronous Buck-Boost MAIN/CAMERA White LED Driver

LTC3452
Synchronous Buck-Boost
MAIN/CAMERA White LED Driver
FEATURES
■ _{High Efficiency: ≥85% Over Entire Li-Ion Battery}
Range
■ _{Wide VIN Range: 2.7V to 5.5V}
■ _{Independent MAIN/CAMERA Current Control}
■ _{Up to 425mA Continuous Output Current}
■ _{Internal Soft-Start}
■ _{Open/Shorted LED Protection}
■ _{PWM Brightness Control}
■ _{LED Current Matching Typically <2.5%}
■ _{Constant Frequency 1MHz Operation}
■ _{Low Shutdown Current: 6.5µA}
■ _{Overtemperature Protection}
■ _{Small Thermally Enhanced 20-Lead}
(4mm × 4mm) QFN Package
U
APPLICATIO S
■ _{Cell Phones}
■ _{Digital Cameras}
■ _PDAs
■ _{Portable Devices}
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
DESCRIPTIO
The LTC^®3452 is a synchronous buck-boost DC/DC con-
verter optimized for driving two banks of white LEDs from
a single Li-Ion battery input. Five parallel LEDs can be
driven at up to 25mA each in the low power LED bank,
while two LEDs can be driven at up to 150mA each (or a
single LED at 300mA) in the high power LED bank. The
regulator operates in either synchronous buck, synchro-
nous boost or buck-boost mode, depending on input
voltage and LED maximum forward voltage. Optimum
efficiency is achieved by sensing which LED requires the
largest forward voltage drop at its programmed current,
and regulating the common output rail for lowest dropout.
Efficiency of 85% can be achieved over the entire usable
range of a Li-Ion battery (2.7V to 4.2V).
Maximum LED current for each LED display is program-
mable with a single external resistor. Dual enable pins
allow for PWM brightness control in the low power bank
and independent on/off control for the high current bank
(optimal for LED camera flash). In shutdown, the supply
current is only 6.5µA.
A high constant operating frequency of 1MHz allows the
use of a small external inductor. The LTC3452 is offered
in a low profile (0.75mm) thermally enhanced 20-lead
(4mm × 4mm) QFN package.
TYPICAL APPLICATIO
V_IN
SINGLE
+
Li-Ion CELL
2.7V TO 4.2V
5 × 20mA White LED Display + 200mA Camera Light Driver
L
4.7µH
2.2µF
V_IN PV_IN SW1
EN_H
SW2 V_OUT
D1
CAM
LED_H1
200mA
I_SETH
LED_H2
6.19k
V_C
0.1µF
EN_L
I_SETL
1MHz
BUCK/BOOST
LTC3452
LED_L1
LED_L2
LED_L3
LED_L4
LED_L5
D2
0mA TO
20mA
D3
0mA TO D4
20mA
0mA TO D5
20mA
0mA TO D6
20mA
0mA TO
20mA
4.7µF
10.2k
GND
GND
PGND EXPOSED PAD
MAIN DISPLAY LED BACKLIGHT
D1: AOT 2015
D2 TO D6: NICHIA NSCW100
L: COILCRAFT DO3314-472
3452 TA01a
Torch and Flash Mode Efficiency
95
93
91
T_A = 25°C
EFFICIENCY
=
Σ
(V_OUT
– V_LEDx) •
V_IN • I_IN
I_LEDx
89 _{TORCH MODE AT 100mA}
87
85
83
81 ^{FLASH MODE AT 200mA}
79
77
75
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
V_IN (V)
3452 TA01b
3452f
1