LTC3217_15 Datasheet, PDF (1/12 Pages) Linear Technology – 600mA Low Noise Multi-LED Camera Light Charge Pumps

FEATURES
n _{Charge Pump Provides High Efficiency with}
Automatic Mode Switching
n _{Multimode Operation: 1x, 1.5x, 2x}
n _{Four Low Dropout LED Outputs}
n _{Up to 600mA Total Output Current}
n _{Independent Torch and Flash ISET and Enable Pins}
n _{Low Noise Constant Frequency Operation*}
n _{PWM Brightness Control via the EN2 Pin}
n _{Low Shutdown Current: 4μA}
n _{Internal Soft-Start Limits Inrush Current During}
Start-Up and Mode Switching
n _{Open/Short LED Protection}
n _{No Inductors}
n _{(3mm x 3mm) 16-Lead QFN Plastic Package}
APPLICATIONS
n _{Multi-LED Camera Light Supply for Cellphones/}
DSCs/PDAs
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. *Protected by U.S. Patents including
6411531.
LTC3217
600mA Low Noise
Multi-LED Camera Light
Charge Pumps
DESCRIPTION
The LTC^®3217 is a low noise charge pump DC/DC converter
designed to power four high current LEDs. The LTC3217
requires only four small ceramic capacitors and two cur-
rent set resistors to form a complete LED power supply
and current controller.
Built-in soft-start circuitry prevents excessive inrush cur-
rent during start-up and mode changes. High switching
frequency enables the use of small external capacitors.
Independent high and low current settings are programmed
by two external resistors. Shutdown mode and current
output levels are selected via two logic inputs.
The current through the LEDs is programmed via I_SET1
and I_SET2. In addition, the brightness can be controlled
by pulse width modulation of the EN2 pin.
The charge pump optimizes efficiency based on the volt-
age across the LED current sources. The part powers up
in 1x mode and will automatically switch to boost mode
whenever any enabled LED current source begins to enter
dropout. The first dropout switches the part into 1.5x
mode and a subsequent dropout switches the part into
2x mode. The LTC3217 resets to 1x mode whenever the
part is shut down.
The LTC3217 is available in a low profile 16-lead
(3mm × 3mm × 0.75mm) QFN package.
TYPICAL APPLICATION
C2
2.2μF
C3
2.2μF
VBAT
C1
2.2μF
EN1 (TORCH)
EN2 (FLASH)
C1P C1M C2P C2M
VBAT
CPO
LTC3217
EN1
EN2
ISET1
ISET2
LED1
LED2
LED3
LED4
GND
19.6k
1%
6.49k
1%
C4
2.2μF
AOT-2015HPW-1751B
EN1 EN2
I_LED
0
0 0 (SHUTDOWN)
1
0
25mA/LED
0
1
75mA/LED
1
1
100mA/LED
3217 TA01
Efficiency vs V_BAT
100
100mA _200mA
90
80
400mA
70
60
50
40
30
20
TOTAL OUTPUT CURRENT
10 P_LED/PIN
LED = 2015 HPW AOT
0
3 3.2 3.4 3.6 3.8 4 4.2 4.4
V_BAT (V)
3217 TA01b
3217fa
1