AAT3123 ETC, AAT3123 Datasheet - Page 7
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AAT3123
Manufacturer Part Number
AAT3123
Description
High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
Manufacturer
ETC
Datasheet
1.AAT3123.pdf
(18 pages)
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Functional Block Diagram
Functional Description
The AAT3123/24 is a dual mode Load Switch (1X)
and high efficiency (1.5X) fractional charge pump
device intended for white LED back light applica-
tions. The fractional charge pump consists of a low
dropout linear voltage regulator followed by a 1.5X
charge pump with multiple current-source outputs.
To maximize power conversion efficiency an internal
feedback 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 over all device effi-
ciency when the input voltage level is greater then
the voltage required at the constant current source
outputs. For the AAT3123, the 1X Load Switch / 1.5X
charge pump mode is decided on the voltage sensed
on the output D1. The AAT3124 bases the 1X Load
Switch/1.5X charge pump mode decision is based
on the voltage levels sensed on either the output D1-
D4 output group or the D5-D6 output group, which
ever is greater. Switchover between the 1.5X
(charge-pump) operating mode and the 1X (load
switch) mode occurs automatically (as a function of
input and output voltages) and does not require user
intervention to maintain maximum efficiency.
3123.2003.09.1.1
EN/SET
Interface
S
2
Cwire
Reference
Reference
Soft Start
Oscillator
Voltage
Control
Current
Current
1MHz
32 x 8 bit
ROM
High Efficiency 1X/1.5X Fractional Charge
GND
Pump for White LED Applications
The AAT3123/24 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 (C
ic output capacitor (C
pump output is converted into four (D1 to D4) or six
(D1-D4 and D5-D6) constant current outputs to drive
four or six individual LEDs with a maximum current of
20mA each. The current source output magnitude is
controlled by the EN/SET serial data S
The interface records rising edges of the EN/SET pin,
and decodes them into 32 individual current level set-
tings each 1dB apart (see Current Level Settings
below). Code 32 is full scale, and Code 1 is full scale
attenuated by 31dB. The modulo 32 interface wraps
states back to state 1 after the 32nd clock.
With each EN/SET pulse, the output current increas-
es by 1dB. To decrease the output current by 1dB, 31
EN/SET clock pulses are required. The counter can
be clocked at speeds up to 1MHz, so intermediate
states are not visible. The first rising edge of EN/SET
enables the IC and initially sets the output LED cur-
rent to -31dB, the lowest setting equal to 525µA.
Once the final clock cycle is input for the desired
brightness level, the EN/SET pin is held high to main-
tain the device output current at the programmed
level. The device is disabled 500µs after the EN/SET
pin transitions to a logic low state.
Charge
1x/1.5x
Pump
Output
Output
Quad
DAC
Dual
DAC
VIN
C1+
C1-
C2+
C2-
OUT
D1
D2
D3
D4
D5*
D6*
*AAT 3124 only
IN
) and one 0.33µF to 1µF ceram-
OUT
). The LDO/1.5X charge
2
C interface.
7