Datasheet
BCR420UW6 / BCR421UW6
Document number: DS37667 Rev. 3 - 2
9 of 13
www.diodes.com
November 2015
© Diodes Incorporated
BCR420UW6 / BCR421UW6
Application Information
Figure 1 Typical Application Circuit for
Linear Mode Current Sink LED Driver
Figure 2 Application Circuit for Increasing LED Current
The BCR420/1 are designed for driving low current LEDs with typical
LED currents of 10mA to 350mA. They provide a cost-effective way for
driving low current LEDs compared with more complex switching
regulator solutions. Furthermore, they reduce the PCB board area of the
solution as there is no need for external components like inductors,
capacitors and switching diodes.
Figure 1 shows a typical application circuit diagram for driving an LED
or string of LEDs. The device comes with an internal resistor (R
INT
) of
typically 95Ω, which in the absence of an external resistor, sets an LED
current of 10mA (typical) from a V
EN
= 3.3V and V
OUT
= 1.4V for
BCR421; or V
EN
= 24V and V
OUT
= 1.4V for BCR420. LED current can
be increased to a desired value by choosing an appropriate external
resistor, R
EXT.
The R
EXT
Vs I
OUT
graphs should be used to select the appropriate
resistor. Choosing a low tolerance R
EXT
will improve the overall
accuracy of the current sense formed by the parallel connection of R
INT
and R
EXT.
Two or more BCR420/1s can be connected in parallel to construct
higher current LED strings as shown in Figure 2. Consideration of the
expected linear mode power dissipation must be factored into the
design, with respect to the BCR420/1’s thermal resistance. The
maximum voltage across the device can be calculated by taking the
maximum supply voltage and subtracting the voltage across the LED
string.
V
OUT
= V
S
– V
LED
P
D
= (V
OUT
× I
LED
)
+ (V
EN
× I
EN
)
As the output current of BCR420/1 increases, it is necessary to provide
appropriate thermal relief to the device. The power dissipation
supported by the device is dependent upon the PCB board material, the
copper area and the ambient temperature. The maximum dissipation
the device can handle is given by:
P
D
= ( T
J(MAX)
- T
A
) / R
θJA
Refer to the thermal characteristic graphs on Page 4 for selecting the
appropriate PCB copper area.