White LED Driver in Tiny SC70 Package Delivers High Efficiency
and Uniform LED Brightness – Design Note 315
David Kim
Introduction
The LTВ®1937 step-up white LED driver is an ideal solution for small battery-powered portable devices such as
cellular phones, PDAs and digital cameras. The LT1937
features an internal 36V switch that is capable of driving up to eight LEDs in series, but it is optimized for
Li-Ion powered color display backlight applications that
use two to four white LEDs. The LT1937 guarantees a
constant light intensity and color in each LED, regardless of differences in their forward voltage drops due
to a constant current step-up architecture that directly
regulates the LED current. The constant 1.2MHz switching allows for the use of tiny external components and
minimizes input and output ripple voltage—meeting
the noise level requirements of products with sensitive
wireless circuitry. The superior internal compensation
of LT1937 lowers the output capacitor requirement to a
single 0.22ОјF ceramic, saving space and cost. The low
95mV feedback voltage and an efficient internal switch
minimize power losses in the LT1937. The result is a
typical efficiency of 84%. The LT1937 is available in the
tiny SC70 or 1mm tall ThinSOTв„ў package.
Li-Ion Powered Driver for Three White LEDs
Figure 1 shows a white LED driver circuit that is …