High Current, High Efficiency Charge Pump
Functional Block Diagram
C1+
C1-
C2+
C2-
AAT3174
VIN
Charge Pump
Section 1
Charge Pump
Section 2
1MHz
Oscillator
Soft-Start
Control
OUT
FL
EN/SET
System Control;
S
2
Cwire;
Timing
RSET
GND
Functional Description
The AAT3174 is a high efficiency, low noise, dual
stage tri-mode 1X/1.5X/2X charge pump device
intended for photo-flash LED applications. The
device requires only four external components: two
ceramic capacitors for the charge pump flying
capacitors, one ceramic capacitor for C
IN
, and one
ceramic capacitor for C
OUT
.
The charge pump is designed to deliver regulated
load currents up to 800mA. The dual stage charge
pump section contains soft-start circuitry to pro-
hibit excessive inrush current during start-up.
System efficiency is maximized with a tri-mode,
dual stage charge pump topology. The internal
clock oscillator at 1MHz allows the use of small
external components.
The tri-mode charge pump operation further opti-
mizes power conversion efficiency. Depending
upon the variance of load current (at different
modes), input voltage, and nominal LED forward
voltage, the charge pump will operate in a 1X, 1.5X,
or 2X mode to generate the output voltage required
to power the load for a given controlled constant
current. This results in significant power savings
over voltage doubling architectures, especially
when the LEDs are also operated at lower current
levels in movie, viewing, or flashlight modes.
S
2
Cwire Serial Interface
The AAT3174 utilizes Analogic Tech's single wire
S
2
Cwire interface to enable/disable the charge
pump and adjust the output current at 16 current
levels. Each code defines the output current to be
a percentage of the maximum current set by the
resistor at the R
SET
pin (see Table 1).
3174.2006.05.1.2
8
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
