PR4401 Datasheet, PDF (8/12 Pages) List of Unclassifed Manufacturers – 0.9V Boost Driver for White LEDs PR4401/4402 Requires Only One External Component

LED DRIVER PR4401/PR4402
Operation of LED with smoothed current (rectifier)
With a diode (preferably a Schottky diode) and a smoothing capacitor the voltage at the
LED can be buffered if necessary. The capacitance must be small enough so that the
voltage at the capacitor will exceed a voltage of 2.5V in the first cycle, otherwise the circuit
may not start up. In most cases, values between 100nF and 1µF are appropriate.
Due to different load characteristics, output current and efficiency are typically higher than
without capacitor, especially in the high-current range.
Vbat =1.2V or 1.5V ^L1
S
Vcc
Vout
Gnd
PR4401/02
White
LED
Recommended configuration for higher LEDs currents
While for lower LED currents it is possible to operate PR4401 with the minimum number
of components, it is recommended to provide both rectifier circuit a the output and buffer
capacitor at the input at high LED currents, to achieve the best performance.
Vbat =1.2V or 1.5V
L1
S
Vcc
Vout
Gnd
PR4401/02
White
LED
Whether the extra components are necessary or not depends largely on the performance
of the components used, most importantly the peak current of the LED, the internal
resistance of the battery and the resistance of the battery cables. If by adding the extra
components the mean LED current increases significantly, it is usually advisable to add
them permanently to achieve a high efficiency.
As a rule of thumb, with a 22µH inductor the extra components will usually not increase
the current significantly, while for inductors below 10µH they will usually improve the
performance noticeably.
Buffer capacitor and rectifier circuit are independent measures. For powerful LEDs, or two
or more LEDs in parallel at the output, the rectifier may not be necessary, but the buffer
capacitor will still prevent high voltage drops along the supply wire.
For the buffer capacitor, values between 220nF and 1µF are common.
© PREMA Semiconductor GmbH 2006-2008
Page 8/12
Rev 0908