On Semi公司的CAT3649是具有32种调光亮度的六路四模式LED驱动器，提供4种电荷泵模式(1倍、1.33倍、1.5倍及2倍)， 这种分数型电荷泵支持从2.4 V到5.5 V的宽输入电压范围。LED电流可以通过单线(1-wire)接口以32个线性增量的模拟调光来调节，也可以通过PWM作进一步的调节，广泛用于最新的智能手机及其它消费类手持应用，如数码相机和便携式媒体播放器(PMP)。本文介绍了CAT3649主要特性，功能方框图以及典型应用电路.

 The CAT3649 is a high efficiency QuadModefractional charge pump that can drive up to six LEDs. The inclusion of a 1.33x fractional charge pump mode increases the device efficiency by up to 10% over traditional 1.5x charge pumps with no added external capacitors.

 Low noise input ripple is achieved by operating at a constant switching frequency which allows the use of small external ceramic capacitors. The multifractional charge pump supports a wide range of input voltages from 2.4 V to 5.5 V.

 The LED current can be adjusted in different ways. The fullscale LED current is set to 25 mA once the device is enabled. Analog dimming in 32 linear steps is achieved via a 1wire pulsedimming input (ADIM).

 Further adjustment of the LED current can be done by applying a pulse width modulation (PWM) signal on the PWM input. The PWM dimming control is compatible with content adaptive brightness control (CABC) for a wide range of PWM signal frequency up to 200 kHz.

 The CAT3649 can be shut down by holding the ADIM or PWM input in a logic low condition for greater than 30 ms. ON Semiconductor’s QuadMode 1.33x charge pump switching architecture is patented.

 CAT3649主要特性:

High Efficiency 1.33x Charge Pump

Quadmode Charge Pump: 1x， 1.33x， 1.5x， 2x

Drives up to 6 LEDs at 25 mA Each

PWM Dimming 100 Hz to 200 kHz for CABC

1wire EZDim_ 32 Linear Steps (ADIM)

Power Efficiency up to 92%

Low Noise Input Ripple in All Modes

“Zero” Current Shutdown Mode

Soft Start and Current Limiting

Short Circuit Protection

Thermal Shutdown Protection

3 mm x 3 mm， 16pad TQFN Package

This Device is PbFree， Halogen Free/BFR Free and is RoHS Compliant

CAT3649典型应用:

LCD Display Backlight

Cellular Phones

Digital Still Cameras

Handheld Devices

图1.CAT3649功能方框图