ANX6929

     The ANX6929 is a highly compact white LED driver especially optimized for thin-film transistor (TFT) liquid crystal displays (LCDs) backlight. The chip can drive up to six strings of LEDs and up to 12 LEDs in series per string. Wide input

voltage range from 2.7V to 24V makes ANX6929 well suited for applications ranging from a one-

cell lithium-ion battery tablet PC to a full-size notebook PC.

     The ANX6929 controls LED dimming through selectable dimming mode, the direct PWM dimming, the analog/PWM mixed dimming, and pure analog dimming. During direct PWM mode, the LED current is turned on and off in response to the duty cycle and frequency applied at the PWM pin. During analog and PWM mixed dimming mode, the input PWM signal is translated to analog signal to control the LED current linearly over 25% to 100% duty. Below 25%, the analog signal will translate to PWM duty cycle information to control the on/off of LED current and average the current down to 1%, the frequency is same as the input PWM frequency for Mode 1, and the frequency is 26kHz for Mode 2. During the analog dimming the LED current of each channel varies linearly depending on the duty cycle of input PWM signal.

     The ANX6929 offers a built-in high efficiency current mode boost converter. The six integrated current sink regulators provide high precision current regulation and matching for LED currents up to 25mA. The feedback loop senses LED current sink voltages and compensates for the non-uniformity of the LED forward voltage accumulated on the LED strings. To minimize the power loss, the output voltage of the boost converter is automatically adjusted by monitoring the highest forward voltage of the LED strings. An unused LED channel can be disabled by connecting the channel to ground.

     The ANX6929 features several protection functions including overcurrent protection (OCP), overtemperature protection (OTP), overvoltage protection (OVP), and LED string open and short detection.