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PDF BCR402 Data sheet ( Hoja de datos )
| Número de pieza | BCR402 | |
| Descripción | Light Emitting Diode (LED) Driver IC Provides Constant LED Current Independent of Supply Voltage Variation | |
| Fabricantes | Infineon Technologies AG | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de BCR402 (archivo pdf) en la parte inferior de esta página. Total 8 Páginas | ||
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Applications Note No. 066
Silicon Discretes
BCR402R: Light Emitting Diode (LED) Driver IC Provides
Constant LED Current Independent of Supply Voltage Variation
• 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 – 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’s 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 “burned” or wasted
as heat in these series resistors.
Infineon’s 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’s
cover the most commonly used LED supply
current ranges – 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 – for BCR401R / 402R,
connect this resistor between pins 3 and 4.
Figure 1. Infineon LED Current Driver Family
Recommended Current Ranges.
Device
BCR401R
BCR402R
Package
SOT143R
SOT143R
Recommended
Current Range
10 – 60 mA
20 – 60 mA
Maximum
Power
Dissipation
330 mW *
330 mW *
BCR402U SC74
20 – 65 mA
BCR405U SC74
50 – 65 mA
* Soldering Point Temperature TS = 87 °C
** Soldering Point Temperature TS = 117 °C
500 mW **
500 mW **
For selecting the proper resistor value to
increase BCR402 drive current above the
nominal level of 20mA, refer to Figure 3, which
AN 066 Rev D
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16-Jan-2004
1 page  
Applications Note No. 066
Silicon Discretes
When used in this way, the BCR402R acts as a
“current sink” for the diodes D1, D2, …, DN on the
top stack of LEDs, and as a “current source” for
the diodes below, e.g. DN+1, DN+2, …, DN+X. As
there is only one current path, stabilization is
maintained for both upper and lower stacks of
LEDs. There is a vanishingly small difference or
“error” in terms of the current difference between
LEDs in the top stack and the bottom stack, this
difference being created by the base current
consumed by the internal PNP transistor in the
BCR402R. This base current, and therefore the
current difference between top and bottom LED
stacks, is only about 400 microamps at a
nominal 20mA LED current. As such, the
human eye will not be able to discern any
differences in brightness in LEDs between top
and bottom stacks due to this effect. In fact,
there is far more variation in brightness between
individual LEDs of the same type, if they are all
driven with identical currents, than could be
attributed to this small “error” current due to the
BCR402R’s PNP transistor base current.
In closing, for either the high voltage application,
or standard application, an external NPN
transistor (Q1) may be used as an ON / OFF
switch for the LED circuit, if desired. Infineon
Technologies markets a broad range of
switching transistors suitable for this purpose,
and the best choice will depend on the voltage
present at pin 1 of the BCR402R, e.g. select a
switching transistor with sufficient collector-
emitter and collector-base breakdown voltages.
Figure 7. Operation of BCR402R at “High” Voltages e.g. > 18V.
+VS
D1
D1, D2, ..., DN:
Use enough LEDs in
"top LED stack" such
that voltage at pin 3 of
BCR402R is < 18V
R1
D2
DN
Note: maximum possible number of LEDs that can be used in
entire circuit depends upon +VS & voltage drop across particular
diode types. Q1 and R2 are optional, if it is desired to switch LED
stack on and off at this point. If switch is not needed, ground pin
1 of BCR402R. Be sure Q1 can handle voltage present at pin 1
of BCR402R given the value of +VS selected. Infineon produces
a broad range of switching transistors suitable for Q1.
ON / OFF
Control
(High = ON)
43
W6s
BCR402R
12
R2
1K
Q1
DN+1
DN+2
DN+X
DN+1, DN+2, ..., DN+X:
Use maximum number of
LEDs in "bottom stack" that
permits sufficient voltage
between pin 2 and ground to
drive them.
AN 066 Rev D
5/ 8
16-Jan-2004
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet BCR402.PDF ] | |
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