AAT3166 データシートの表示（PDF） - Analog Technology Inc

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AAT3166

High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications

Analog Technology Inc 

AAT3166

High Efficiency 1X/1.5X/2X Charge

Pump for White LED Applications

AS2Cwire Serial Interface Timing

EN/SET

Address

Address

THI

TLO

TLAT

1

2

17

18

0

Data

TLAT

1

2 . . . n <= 16

1

Data Reg 1

Data Reg 2

0

n-1

0

Applications Information

LED Selection

Although the AAT3166 is designed for driving white

LEDs, the device also can be used to drive most

types of LEDs with forward voltage specifications

ranging from 2.0V to 4.7V. LED applications may

include main and sub-LCD display backlighting,

camera photo-flash applications, color (RGB)

LEDs, infrared (IR) diodes for remotes, and other

loads benefiting from a controlled output current

generated from a varying input voltage. Since the

D1 to D4 input current sinks are matched with neg-

ligible voltage dependence, the LED brightness will

be matched regardless of the specific LED forward

voltage (VF) levels.

In some instances (e.g., in high-luminous-output

applications such as photo flash), it may be neces-

sary to drive high-VF type LEDs. The low-dropout

current sinks in the AAT3166 make it capable of

driving LEDs with forward voltages as high as 4.7V

at full current from an input supply as low as 3.0V.

Outputs can be paralleled to drive high-current

LEDs without complication.

Device Switching Noise Performance

The AAT3166 operates at a fixed frequency of

approximately 1MHz to control noise and limit har-

monics that can interfere with the RF operation of

cellular telephone handsets or other communica-

tion devices. Back-injected noise appearing on the

input pin of the charge pump is 20mV peak-to-

peak, typically ten times less than inductor-based

DC/DC boost converter white LED backlight solu-

tions. The AAT3166 soft-start feature prevents

noise transient effects associated with inrush cur-

rents during start-up of the charge pump circuit.

Capacitor Selection

Careful selection of the four external capacitors

(CIN, C1, C2, COUT) is important because they will

affect turn-on time, output ripple, and transient per-

formance. Optimum performance will be obtained

when low equivalent series resistance (ESR)

ceramic capacitors are used; in general, low ESR

may be defined as less than 100mΩ. A value of

1µF for all four capacitors is a good starting point

when choosing capacitors. If the LED current

sources are programmed only for light current lev-

els, then the capacitor size may be decreased.

3166.2006.05.1.2

11

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