AAT3123ITP-20-T1 View Datasheet(PDF) - Advanced Analogic Technologies

Part Name

Description

MFG CO.

AAT3123ITP-20-T1

High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications

Advanced Analogic Technologies 

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PRODUCT DATASHEET

AAT3123/23A/24

ChargePumpTM High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications

However, if the diodes are dramatically different in type

comprising a mix of high-VF and low-VF LEDs, the

AAT3124 has the capability to optimally and simultane-

ously drive up to four LEDs of one type and up to two

LEDs of another type. Such a feature can be useful for

driving different color LEDs; driving both display back-

light and photo-flash LEDs; or for driving main-LCD and

sub-LCD display LED backlights from a single charge

pump IC.

For example, when driving independent RGB LEDs, the

green and blue LEDs typically require a high VF to operate

(e.g., 3.7V), while the red LED needs a low forward volt-

age (e.g., 2V). By connecting the green and blue diodes

to outputs D1 to D4 and the red diodes to D5 and D6,

good control and uniformity in brightness are maintained

despite the 2V difference in the diode forward voltages.

The AAT3124 determines if the 1.5X charge pump circuit

is needed based on the voltage on D1 and D5, whichever

is higher. If adequate voltage is available to drive the

higher voltage LED (of output D1 or D5) without the

charge pump running, the IC automatically switches into

step-down (1X) mode to maximize efficiency.

Similarly, if a 4V photo-flash LED array is connected to

outputs D1 through D4 (with the outputs shorted togeth-

er) and two 3.3V sub-LCD-display backlight LEDs are

connected to outputs D5 and D6, then the AAT3124 can

optimally drive each set of LEDs at the programmed cur-

rent level (see application schematics). The photo flash

can be disabled by an N-channel switch connected in

series with the photo-flash LED.

The AAT3123/23A/24 has only one programmed value of

current and does not allow for separate on/off or bright-

ness control of each current source output. This limita-

tion can easily be circumvented by introducing grounded

source N-channel MOSFET switches in series with the

LEDs to turn any given LED (or bank of LEDs) on or off.

The various LEDs can be turned on and off indepen-

dently, simultaneously, or multiplexed to produce any

variety of lighting effects. By reprogramming the current

source (via the serial interface) between switching tran-

sitions, the brightness of individual LEDs or banks of

LEDs can also be controlled.

Charge Pump Compatibility

The four-output AAT3123 is pin compatible with the

AAT3113 in both QFN and TSOPJW packages. The six-

output AAT3124 is pin compatible with the AAT3114 in

the QFN package. Compared to the AAT3113/14, the

AAT3123/23A/24 offers an improved overall efficiency,

wider operating range, and the ability to drive high-VF

LEDs (up to 4.3V) at full current from a 3V input condi-

tion. The AAT3123/23A/24 is well suited for battery-

powered applications using single-cell lithium-ion (li-ion)

batteries (4.2V to 2.8V), lithium-polymer batteries, and

3-series connected dry cells (3.6V).

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3123.2008.03.1.5

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