A super-high efficiency dc/dc boost converter for driving white LEDs and biasing Notebook PC LCD panels is now available from Micrel Semiconductor, an industry leader in analog and power management integrated circuits.

With a 2.4V to 16V input voltage range, and a low shutdown current of only <1uA, the MIC2145 is ideal for portable, low input voltage applications.

Leading edge cell phones and PDAs are using white LEDs as the solution of choice for backlighting color LCDs. With an integrated 1.5A switch, the MIC2145 can easily drive four white LEDs for cellular applications, or up to 10 white LEDs for larger panel PDA applications.

A unique peak-current-set feature allows designers to program the peak switch current to the level, which allows maximum efficiency. This feature allows the MIC2145 to be highly efficient in a wide range of applications and load currents.

In Notebook PC applications, the MIC2145 efficiently boosts the readily available 3.3V or 5V supply to provide the required LCD bias for TFT displays. A soft-start feature reduces power supply noise associated with in-rush current. Separate analog and power grounds further minimize noise.

There have been a few parts already released for what, so far, has been mainly a Far East market for backlit color LCDs. What is special here is that the output power is increased by a dramatic degree to 2.5 W. This will considerably reduce the component count on the larger PDA applications.

Output voltage is set with a potential divider on the output providing a feedback voltage to be compared to the on-chip reference. Soft start is engineered to reduce noise and there are both current limit and thermal shutdown protections. With an input voltage range of 2.4 to 16 V, the part can be used from a single Li-Ion up to a 3/4-cell NiCd/NiMH combination; the output can be set up to 16 V so the part can therefore be used for the standard 10 to 15 V range for the LEDs as well as being useful for local 3.3 to 5-V conversions. Efficiencies approaching 90% can be achieved with careful design at higher loads and the typical 450 kHz operation is high enough to allow for an inductor of only 10 uH; a Schottky is recommended as the output diode to increase efficiency and the configuration should be bootstrapped for loads higher than 70 mA. The quiescent current is 200 uA with a shutdown of typically 0.5 uA.