鈥?/div>
Supplies stable bias current for Light Emitting Diodes (LEDs)
Low Voltage Drop of 0.75V maximizes system DC efficiency
LED drive current adjustable via single external resistor (20 鈥?60 mA range)
Negative temperature coefficient protects LEDs against thermal runaway
Low Cost, Low External Parts Count, Easy-to-Use, Fast Time-To-Market
Small Surface-Mount SOT143R packaging (2.9 x 1.6 x 1.1 mm inc. leads)
1. Introduction
Light-Emitting Diodes (LEDs) and LED displays
suffer from varying illumination levels as a result
of changes in power supply voltages. This is
true for displays used in automotive applications,
battery-operated handheld devices, or fixed
(architectural) installations.
To keep LED
brightness constant, it is necessary to stabilize
the LED鈥檚 current over the anticipated power
supply voltage variation range.
Often a resistor in series with the LED(s) is used
to stabilize current. However, this method has
some serious drawbacks. To achieve good LED
current stability over the varying supply voltage
range, the resistor must take on a large value
(infinite resistance, in the ideal case) to make
the power supply plus series resistor
combination approach the traits of an ideal
constant current source having infinite output
impedance. In such cases, there is a large
voltage drop across this series resistor. For a
particular supply voltage, this voltage drop 1)
reduces the number of LEDs that can be driven
by one resistor, requiring additional parallel
resistors with which to drive a given number of
LEDs, thereby increasing system current
consumption and 2) power is 鈥渂urned鈥?or wasted
as heat in these series resistors.
AN 066 Rev D
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Infineon鈥檚 LED driver family, consisting of
the BCR401R, BCR402R, BCR402U and
BCR405U,
offers an easy, cost-effective and
reliable way to achieve LED current stabilization
while overcoming the drawbacks inherent in
using a series resistor. These LED driver IC鈥檚
cover the most commonly used LED supply
current ranges 鈥?10mA, 20mA, and 50mA.
Refer to
Figures 1 and 2.
In each device, the
nominal drive current may be easily adjusted
upward from the nominal value by adding a
single external resistor 鈥?for BCR401R / 402R,
connect this resistor between pins 3 and 4.
Figure 1. Infineon LED Current Driver Family
Recommended Current Ranges.
Device
BCR401R
BCR402R
BCR402U
BCR405U
Package
SOT143R
SOT143R
SC74
SC74
Recommended
Current Range
10 鈥?60 mA
20 鈥?60 mA
20 鈥?65 mA
50 鈥?65 mA
Maximum
Power
Dissipation
330 mW *
330 mW *
500 mW **
500 mW **
* Soldering Point Temperature T
S
= 87
擄C
** Soldering Point Temperature T
S
= 117
擄C
For selecting the proper resistor value to
increase BCR402 drive current above the
nominal level of 20mA, refer to
Figure 3,
which
16-Jan-2004
INFINEON
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