AAT3119 Datasheet, PDF (10/18 Pages) Advanced Analogic Technologies – High Efficiency 2X Charge Pump

Functional Block Diagram
IN
AAT3119
High Efficiency 2X Charge Pump
C1+ C1-
Charge
Pump
Soft Start
1MHz
Oscillator
OUT
EN
Voltage
Reference
GND
Functional Description
The AAT3119 is a 5.0V or 4.5V regulated voltage
doubling charge pump device intended for general
applications that require low noise voltage boost
function from input supplies ranging from 2.7V to
5.5V. The charge pump is capable maintaining the
regulated voltage output for continuous output cur-
rent loads up to 150mA. This makes the AAT3119
ideal for general purpose voltage boost applica-
tions, driving white and RGB color LEDs, as well as
USB OTG V_BUS supplies in portable products. The
AAT3119 charge pump and regulation circuit is
also capable of supplying peak pulse currents up to
250mA for 500ms. This makes the device suitable
for many photo-flash LED applications.
The AAT3119 accomplishes the voltage boost func-
tion by utilizing a voltage doubling (2X) charge
pump. The charge pump block within the device
uses low R_DS MOSFET switches to transfer charge
from the input to output via a flying capacitor (C_FLY).
This switching process is performed over two phas-
es of each clock cycle which is set by the fixed
1.2MHz internal oscillator. On the first phase of
each clock cycle, the flying capacitor is placed in
parallel with the input (IN) and is charged to the
level of the input voltage across C_IN. On the second
10
phase of the switching cycle, the flying capacitor is
reconfigured by the internal switches and placed in
series with the input capacitor. C_IN and C_FLY are
then placed across the output capacitor (C_OUT).
The voltage seen on C_OUT is then two times that of
C_IN. The AAT3119 contains an internal reference
and feedback system that senses the charge pump
output and controls the charge pump function to
maintain an accurate regulated output voltage.
Because of the fixed 1.2MHz high frequency inter-
nal oscillator, the input, output, and flying capaci-
tors are very small. This circuit architecture
requires only one 1μF ceramic capacitor for the
charge pump flying capacitor (C_FLY) and one 1μF
ceramic capacitor for both C_IN and C_OUT.
The AAT3119 has a soft-start circuit to prohibit in-
rush current when the device is enabled. This fea-
ture guarantees a smooth transition to the desired
output voltage when the device is turned on. The
system soft-start circuit is particularly useful in
white LED backlight applications where the use of
a PWM signal is employed as an LED dimming
function. In limiting the input inrush current each
time the device is turned on, the soft-start circuit
helps minimize back-injected switching noise and
transient supply current.
3119.2007.02.1.2