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 Quad−Modefractional 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 multi−fractional 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 full−scale LED current is set to 25 mA once the device is enabled. Analog dimming in 32 linear steps is achieved via a 1−wire pulse−dimming 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 Quad−Mode 1.33x charge pump switching architecture is patented.

 CAT3649主要特性:

High Efficiency 1.33x Charge Pump

Quad−mode 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

1−wire 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， 16−pad TQFN Package

This Device is Pb−Free， 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