Synchronous Down-Boost White LED Driver

Linear Technology Corporation has introduced the LTC3452, a synchronous buck-boost DC/DC converter that optimizes the use of a single-cell Li-Ion battery to drive two sets of white LEDs . The LTC3452 can drive up to five LEDs in parallel, and each LED has a drive current of up to 25mA, which provides backlighting for the LCD display. The device also drives two LEDs with a drive current of up to 200mA (or one LED and a drive current of 400mA) for camera flash applications. The LTC3452's synchronous buck-boost topology provides up to 90% efficiency over the entire available Li-Ion battery voltage range of 2.7V to 4.2V, maximizing battery run time. The 4mm x 4mm QFN package and constant 1MHz switching frequency ensure a very compact solution footprint for most handheld applications.

Depending on the input voltage and the highest forward voltage drop of the LED, the LTC3452 can operate in either synchronous buck, synchronous buck, or buck-boost mode. Optimal efficiency is achieved by detecting which LED requires the highest forward voltage drop at the programming current and adjusting the common output rail to achieve the lowest differential pressure. The maximum LED current for each display can be programmed with a single external resistor. The dual enable pin allows PWM brightness control of the TFT display while a separate on/off control pin is used for the flash output. Other features include: internal soft-start, open/short LED protection and overtemperature protection.

Performance summary:

High efficiency: ≥ 90% over the entire single-cell lithium battery voltage range
Wide VIN range: 2.7V to 5.5V
Independent main display / camera current control
500mA (total) continuous output current
1MHz constant frequency operation internal soft start open/short LED protection
PWM brightness control overheat protection low shutdown current: 6uA
Small heat-resistant enhanced 16-lead (4mm x 4mm) QFN package