AAT3134
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
Functional Block Diagram
VIN
Soft-Start
Control
C1+
C1-
1X/1.5X
Charge
Pump
C2+
1MHz
Oscillator
C2-
Voltage
Reference
OUT
D1
D2
D3
D4
Current
Reference
Quad
Output
DAC
32x16 bit
ROM
S2Cwire
Interface
Dual
Output
DAC
D5
D6
EN/SET
32x16 bit
ROM
GND
automatically (as a function of input and output volt-
ages) and does not require user intervention to main-
tain maximum efficiency.
Functional Description
The AAT3134 is a dual mode load switch (1X) and
high efficiency (1.5X) fractional charge pump device
intended for white LED backlight applications. The
fractional charge pump consists of a low dropout lin-
ear voltage regulator followed by a 1.5X charge
pump with multiple current source outputs. To maxi-
mize power conversion efficiency, an internal feed-
back control sensing circuit monitors the voltage
required on the constant current source outputs.
This control circuit then sets the load switch and
charge pump functions based upon the input voltage
level versus the output voltage level needed. This
function significantly enhances overall device effi-
ciency when the input voltage level is greater than
the voltage required at the constant current source
outputs. The 1X load switch/1.5X charge pump
mode decision is based on the voltage levels sensed
on either the D1 or D5 output, whichever is greater.
Switchover between the 1.5X (charge pump) operat-
ing mode and the 1X (load switch) mode occurs
The AAT3134 requires only four external compo-
nents: two 1µF ceramic capacitors for the charge
pump flying capacitors (C1 and C2), one 1µF ceram-
ic input capacitor (CIN), and one 0.33µF to 1µF
ceramic output capacitor (COUT). The LDO/1.5X
charge pump output is converted into four (D1 to D4)
constant current outputs to drive four individual LEDs
with a maximum current of 20mA each and two (D5
and D6) constant current outputs with a maximum
current of 20mA. The current source output magni-
tude is controlled by the EN/SET serial data interface.
The interface records rising edges of the EN/SET pin
and decodes them into 32 addresses corresponding
to individual current level settings. The 32 addresses
are divided up such that outputs D1 to D4 can be
controlled independently of outputs D5 to D6. For
Addresses 1 to 6, 7 to 12, 13 to 18, 19 to 24, and 25
to 30, outputs D1 to D4 start at 0mA and increase
from 1mA to 20mA in four steps. Outputs D5 and D6
3134.2005.12.1.1
7
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
