High Current LED Flash Driver Charge Pump IC
Functional Block Diagram
C1+
C1-
C2+
C2-
AAT3170
VIN
Charge Pump
Section 1
Charge Pump
Section 2
1MHz
Oscillator
Soft Start
Control
OUT
F1
EN/SET
System Control;
AS
2
Cwire;
Timing
F2
GND
CT
Functional Description
The AAT3170 is a high efficiency, low noise, dual
stage tri-mode 1X/1.5X/2X charge pump device
intended for photo-flash LED applications. The
AAT3170 requires only four external components:
two 1.0µF ceramic capacitors for the charge pump
flying capacitors, one 4.7µF ceramic capacitor for
C
IN
, and one 2.2µF ceramic capacitor for C
OUT
.
The charge pump is designed to deliver load cur-
rents up to 600mA. The dual stage charge pump
section contains soft-start circuitry to prevent
excessive in-rush current during start-up. System
efficiency is maximized with a tri-mode, dual stage
charge pump topology. The internal clock oscilla-
tor, which operates at 1MHz, allows the use of
small external components.
The tri-mode charge pump architecture optimizes
power conversion efficiency. Depending upon the
combination of load current, input voltage, and
nominal LED forward voltage, the charge pump will
8
operate in a 1X, 1.5X, or 2X mode to generate the
output voltage required to power the load for a pro-
grammed constant current setting. This results in
significant power savings over voltage doubling
architectures, especially when the LEDs are con-
tinuously operated at lower current levels in movie
viewing or flashlight modes.
Constant Current Channels
The AAT3170 contains two programmable constant
current sinks for integrated flash circuit control.
Efficiency is optimized with the low dropout char-
acteristic of the current sinks. The low dropout per-
formance extends the battery operating range for
1X and 1.5X modes, improving efficiency and
extending battery life. Each constant current sink is
programmable through the AS
2
Cwire serial inter-
face. Independent current settings can be used for
a multistage flash LED control. This feature allows
users to conveniently drive separate dual flash
LEDs directly while achieving good brightness
3170.2006.11.1.1
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
