AAT3119
High Efficiency 2X Charge Pump
Functional Block Diagram
C1+ C1-
IN
Charge
Pump
OUT
Soft Start
1MHz
Oscillator
Voltage
Reference
EN
GND
phase of the switching cycle, the flying capacitor is
reconfigured by the internal switches and placed in
series with the input capacitor. CIN and CFLY are
then placed across the output capacitor (COUT).
The voltage seen on COUT is then two times that of
CIN. 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.
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 VBUS 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.
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 (CFLY) and one 1µF
ceramic capacitor for both CIN and COUT
.
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.
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 RDS MOSFET switches to transfer charge
from the input to output via a flying capacitor (CFLY).
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 CIN. On the second
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