LED Backlight Driver with 2PWM Inputs

The AS3674 is an inductive highly efficient DCDC boost converter. The DCDC converter operates at a fixed frequency of 2MHz and includes soft startup to allow easy integration into noise sensitive RF systems.

A predictable startup is guaranteed even with very low duty cycle PWM input signals. The voltage on the output capacitor is controlled to minimize ripple and to avoid any acoustic effects for low frequency PWM input signals. The output of the DCDC converter is used for five current sources connected to up to 10 LEDs. If a current source is not required, it can be safely left open – the AS3674 detects this condition and disables this currentsource automatically; this keep the efficiency of the system constantly high.

The AS3674 is controlled by two enable inputs, ON13 and ON45. These input can also be used to connect a PWM input (like DLS or DBC).

The AS3674 includes several protection function like undervoltage lockout, overcurrent and overtemperature. No microvias are required to assemble the AS3674 if only four channels are used and ON13=ON45. The AS3674 is available in a space-saving WL-CSP package measuring only 1.8×1.4×0.6mm and operates over the -30ºC to +85ºC temperature range.

Key Features

• 2 MHz DCDC Boost converter

Small 4.7μH external coil
Very high system efficiency of 90% (DCDC and current sources)
Very low voltage changes on output to avoid acoustic noise on output capacitor even with PWM
Smooth startup even under low duty cycle PWM conditions

• Five Current sources

Low voltage compliance (100mV)
High side current source to simplify layout and thermal management of the LEDs
Automatically detect and disable failing or not used LEDs to keep efficiency high
Current matching <4%
Current accuracy <7.5%

• Excellent LED current output ripple <2%
• Support DLS (Dynamic Luminance Scaling or DBC)
• Undervoltage lockout and overcurrent protection
• Overtemperature protection
• Available in a tiny WL-CSP package

3×4 balls, 0.4mm pitch, 1.8×1.4×0.6mm

Applications

Display backlight driver for mobile phones, digital cameras, PND and PMPs.