PR4401 Datasheet, PDF (6/12 Pages) List of Unclassifed Manufacturers – 0.9V Boost Driver for White LEDs PR4401/4402 Requires Only One External Component

LED DRIVER PR4401/PR4402
Influence of the LED Forward Voltage
measured with 1 LED / 2 LEDs in parallel; Vcc = 1.5V
Circuit
10 µH, 1 LED
10 µH, 2 LEDs ||
22 µH, 1 LED
22 µH, 2 LEDs ||
LED Peak LED Mean Current
Forward Voltage
5.8 V
20 mA
4.6 V
24 mA
4.2 V
13 mA
3.5 V
14 mA
Mean Supply
Current
70 mA
70 mA
33 mA
32 mA
Efficiency
77 %
80 %
82 %
82 %
Peak forward voltages above approx. 5V are often considered as an overload condition
and may lead to a lower LED efficiency.
Application Notes
Selection of PR4401 and PR4402
The circuit type should be selected according to the required LED current.
PR4401 is best operated with inductors between 10 and 22µH.
PR4402 is best operated with inductors between 4.7 and 10µH.
Using lower inductances may lead to erratic behaviour, especially at low supply voltages
and should be avoided.
Operating with higher inductances is possible and will lead to lower supply and LED
current.
However the quiescent current which is independent of the inductance will lead to a lower
overall efficiency. Since PR4402 has about twice the quiescent current of PR4401, it is not
recommended for small LED currents.
LED compatibility
It must be considered that the peak current through the LED is a factor of up to 7 higher
than the mean current. LED lifetime may be affected if operated outside the range
specified by the LED vendor.
Since the emission spectrum of white LEDs usually depends on the current, the light color
may shift to blueish white. High peak currents may also saturate the LED and reduce the
light efficiency of the LED.
If the rated LED peak current is exceeded, it is recommended to use a smoothing
capacitor and diode to provide a continuous output current (see below). With most
standard LEDs, this will improve the overall performance with inductors of 10µH and less,
or mean output currents of 23mA and more.
Note that with especially with the higher currents of PR4402 the current rating of most
standard LEDs is exceeded, and more powerful or multiple LEDs must be used.
Inductor compatibility
While the series resistance of the coil has a small impact on the LED current, it is
important that the saturation current is higher than the maximum peak current over the
supply voltage range. Inductors optimized for DC-DC converters are mostly suitable.
© PREMA Semiconductor GmbH 2006-2008
Page 6/12
Rev 0908