BCR420UW6 / BCR421UW6
LINEAR LED CONSTANT CURRENT REGULATOR IN SOT26
Description
Features
The BCR420U and BCR421U monolithically integrate transistors,
diodes and resistors to function as a Constant Current Regulator
(CCR) for linear LED driving. The device regulates with a preset
10mA nominal that can be adjusted with an external resistor up to
350mA. It is designed for driving LEDs in strings and will reduce
current at increasing temperatures to self-protect. Operating as a
series linear CCR for LED string current control, it can be used in
multiple applications, as long as the maximum supply voltage to the
device is < 40V.
With the low-side control, the BCR421U has an Enable (EN) pin
which can be pulse-width modulated (PWM) up to 25kHz by a microcontroller for LED dimming.
With no need for additional external components, this CCR is fully
integrated into an SOT26 (SC74R) minimizing PCB area and
component count.
LED Constant Current Regulator using NPN Emitter-Follower with
Emitter Resistor to Current Limit
IOUT – 10mA ± 10% Constant Current (Preset)
IOUT up to 350mA Adjustable with an External Resistor
(BCR421U)
VOUT – 40V Supply Voltage
PD up to 1W in SOT26 (SC74R)
Low-Side Control Enabling PWM Input < 25kHz (BCR421U)
Negative Temperature Coefficient (NTC) Reduces IOUT with
Increasing Temperature
Parallel Devices to Increase Regulated Current
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
Qualified to AEC-Q101 Standards for High Reliability
Automotive-Compliant Parts are Available Under Separate
Datasheet (BCR420UW6Q/BCR421UW6Q)
Mechanical Data
Applications
Constant Current Regulation (CCR) in:
Automotive Interior Lighting
Emergency Lighting
Signage, Advertising, Decorative and Architectural Lighting
Retail Lighting in Fridges, Freezer Cases and Vending Machines
SOT26 (SC74R)
EN
Case: SOT26 (SC74R)
Case Material: Molded Plastic. ―Green‖ Molding Compound.
UL Flammability Rating 94V-0
Moisture Sensitivity: Level 1 per J-STD-020
Terminals: Finish - Matte Tin Plated Leads. Solderable per MILSTD-202, Method 208
Weight: 0.018 grams (Approximate)
OUT
BCR420U
BCR421U
Rext
R
EXT
(Optional)
(Optional)
EN
REXT
Pin Name
OUT
OUT
OUT
EN
OUT
GND
REXT
GND
GND
Top View
Internal Device
Schematic
Pin Function
Regulated Output Current
Enable for Biasing
Transistor
External Resistor for
Adjusting Output Current
Power Ground
Top View
Pin-Out
Ordering Information (Note 4)
Product
BCR420UW6-7
BCR421UW6-7
Notes:
Compliance
AEC-Q101
AEC-Q101
Marking
420
421
Reel Size (inches)
7
7
Tape Width (mm)
8
8
Quantity per Reel
3,000
3,000
1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.
2. See http://www.diodes.com/quality/lead_free.html for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green"
and Lead-free.
3. Halogen- and Antimony-free "Green" products are defined as those which contain 2.0V; VEN = 24V
VOUT > 2.0V; VEN = 3.3V
VOUT > 2.0V; VEN = 24V
VOUT > 2.0V; VEN = 3.3V
June 2017
© Diodes Incorporated
BCR420UW6 / BCR421UW6
1.4
800
1.2
700
Rth(JA) ( C/W)
Max Power Dissipation (W)
Typical Thermal Characteristics BCR420/1U (@TA = +25°C, unless otherwise specified.)
50mm * 50mm
1oz Cu
1.0
o
0.8
0.6
0.4
25mm * 25mm
1oz Cu
0.2
600
500
400
300
200
100
0.0
0
50
100
0
150
100
1000
2
o
Temperature ( C)
Copper Area (mm )
Derating Curve
Rth(JA) VS Cu Area
75
50
Maximum Power (W)
o
T amb=25 C
100
o
Thermal Resistance ( C/W)
125
50mm * 50mm
1oz Cu
D=0.5
Single Pulse
D=0.2
D=0.05
25
D=0.1
0
100μ
µ 1m
10m 100m
1
10
100
o
T amb=25 C
10
1
100μµ 1m
1k
Pulse Width (s)
1
10
100
1k
Pulse Power Dissipation
150
o
125
100
Maximum Power (W)
o
10m 100m
Pulse Width (s)
Transient Thermal Impedance
Thermal Resistance ( C/W)
Single Pulse
50mm * 50mm
1oz Cu
T amb=25 C
25mm * 25mm
1oz Cu
D=0.5
75
50 D=0.2
Single Pulse
D=0.05
25
D=0.1
0
µ
100μ
1m
10m 100m
1
10
100
1k
Single Pulse
o
10
T amb=25 C
25mm * 25mm
1oz Cu
1
100μµ 1m
10m 100m
1
10
100
Pulse Width (s)
Pulse Width (s)
Transient Thermal Impedance
Pulse Power Dissipation
BCR420UW6 / BCR421UW6
Document number: DS37667 Rev. 5 - 2
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1k
June 2017
© Diodes Incorporated
BCR420UW6 / BCR421UW6
Typical Electrical Characteristics BCR421U (Cont.) (@TA = +25°C, unless otherwise specified.)
0.20
0.20
VEN=3.3V
REXT=6.2
REXT=8.2
VOUT=5.4V
0.15
REXT=10
IOUT (A)
IOUT (A)
0.16
0.12
0.08
REXT= 30
REXT=15
VOUT=1.4V
0.10
0.05
0.04
VEN=3.3V
REXT=open
0.000
1
2
3
4
5
6
7
8
9 10 11 12
0.00
1
10
100
REXT ()
VOUT (V)
REXT () vs IOUT
VOUT vs IOUT
0.18
o
-40 C
0.06
0.16
o
-40 C
0.05
IOUT (A)
IOUT (A)
0.14
0.12
o
25 C
0.10
o
85 C
VEN=3.3V
0.08
0.06
0.04
o
25 C
o
85 C
VEN=3.3V
0.03
REXT=20
REXT=6.2
0
2
4
6
8
10
0.02
0
12
VOUT (V)
2
4
6
VOUT (V)
8
10
12
VOUT vs IOUT
VOUT vs IOUT
0.15
0.02
REXT=8.2
VOUT=2V
REXT=6.2
REXT=10
o
IOUT (A)
IOUT (A)
-40 C
0.01
o
85 C
0.00
0
2
4
BCR420UW6 / BCR421UW6
Document number: DS37667 Rev. 5 - 2
6
REXT=30
REXT= 60
0.05
REXT= open
VEN=3.3V
o
25 C
0.10
REXT=open
8
10
12
0.00
0
1
2
3
VOUT (V)
VEN (V)
VOUT vs IOUT
VEN vs IOUT
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5
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© Diodes Incorporated
BCR420UW6 / BCR421UW6
Typical Electrical Characteristics BCR421U (Cont.) (@TA = +25°C, unless otherwise specified.)
0.015
3.0m
o
-40 C
IOUT=0A
o
o
85 C
REXT=open
2.0m
IOUT (A)
IEN (mA)
2.5m
1.5m
1.0m
o
25 C
o
-40 C
25 C
0.010
o
85 C
0.005
VOUT=2V
500.0μ
µ
REXT=open
0.0
0
1
2
3
4
0.000
0
5
1
VEN (V)
2
3
4
5
VEN (V)
VENvs IOUT
VENvs IEN
0.06
0.20
o
-40 C
o
-40 C
0.05
IOUT (A)
IOUT (A)
0.15
0.04
o
o
85 C
25 C
0.03
o
25 C
o
0.10
85 C
0.02
0.01
0.00
VOUT=2V
0.05
VOUT=2V
REXT=6.2
REXT= 20
0
1
2
3
4
5
0.00
0
VENvs IOUT
BCR420UW6 / BCR421UW6
Document number: DS37667 Rev. 5 - 2
1
2
3
4
5
VEN (V)
VEN (V)
VEN vs IOUT
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BCR420UW6 / BCR421UW6
Typical Electrical Characteristics BCR420U (Cont.) (@TA = +25°C, unless otherwise specified.)
0.20
0.20
REXT=6.2
0.16
REXT=8.2
VOUT = 5.4V
0.15
REXT=10
IOUT (A)
IOUT (A)
VEN=24V
0.12
0.08
REXT=15
REXT= 30
0.04
0.10
0.05
VEN=24V
REXT=open
0.00
0
1
2
3
4
5
6
7
VOUT (V)
8
VOUT=1.4V
0.00
1
9 10 11 12
10
100
REXT ()
REXT ()vs IOUT
VOUT vs IOUT
0.18
o
-40 C
0.06
0.16
o
-40 C
IOUT (A)
IOUT (A)
0.14
0.12
o
25 C
0.10
0.04
o
25 C
85 C
VEN=24V
VEN=24V
0.03
REXT=20
REXT=6.2
0
2
4
6
8
10
0.02
0
12
VOUT (V)
2
4
6
VOUT (V)
8
10
12
VOUT vs IOUT
VOUT vs IOUT
0.15
0.02
VOUT=2V
IOUT (A)
IOUT (A)
0.01
o
o
85 C
4
6
0.10
REXT=open
0.05
REXT=open
8
10
12
0.00
0
5
10
15
20
25
30
VEN (V)
VOUT vs IOUT
Document number: DS37667 Rev. 5 - 2
REXT=30
REXT=60
VOUT (V)
BCR420UW6 / BCR421UW6
Rext=10
VEN=24V
25 C
2
REXT=8
REXT=20
o
-40 C
0.00
0
o
85 C
o
0.08
0.06
0.05
VEN vs IOUT
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BCR420UW6 / BCR421UW6
Typical Electrical Characteristics BCR420U (Cont.) (@TA = +25°C, unless otherwise specified.)
0.015
3.0m
o
-40 C
IOUT=0A
o
2.0m
o
85 C
REXT=open
1.5m
1.0m
o
25 C
25 C
0.010
IOUT (A)
IEN (mA)
2.5m
o
85 C
0.005
o
-40 C
VOUT=2V
500.0μ
µ
0.0
0
REXT=open
5
10
15
20
25
30
35
40
0.000
0
5
10
VEN (V)
15
20
25
30
VEN (V)
VENvs IEN
VENvs IOUT
0.06
0.20
o
-40 C
o
-40 C
0.05
o
85 C
25 C
0.03
0.02
VOUT=2V
0.01
0.00
0
o
25 C
o
IOUT (A)
IOUT (A)
0.15
0.04
0.10
o
85 C
VOUT=2V
0.05
REXT=6.2
REXT=20
5
10
15
20
VEN (V)
25
30
0.00
0
Document number: DS37667 Rev. 5 - 2
10
15
VEN (V)
20
25
30
VENvs IOUT
VENvs IOUT
BCR420UW6 / BCR421UW6
5
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BCR420UW6 / BCR421UW6
Application Information
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 (RINT) of
typically 95Ω, which in the absence of an external resistor, sets an LED
current of 10mA (typical) from a VEN = 3.3V and VOUT = 1.4V for
BCR421; or VEN = 24V and VOUT = 1.4V for BCR420. LED current can
be increased to a desired value by choosing an appropriate external
resistor, REXT.
REXT
(Optional)
The REXT vs IOUT graphs should be used to select the appropriate
resistor. Choosing a low tolerance REXT will improve the overall
accuracy of the current sense formed by the parallel connection of RINT
and REXT.
REXT
(Optional)
Figure 1 Typical Application Circuit for
Linear Mode Current Sink LED Driver
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.
VOUT = VS – VLED
PD = (VOUT × ILED) + (VEN × IEN)
REXT
(Optional)
REXT
(Optional)
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:
PD = ( TJ(MAX) - TA) / RθJA
Figure 2 Application Circuit for Increasing LED Current
BCR420UW6 / BCR421UW6
Document number: DS37667 Rev. 5 - 2
Refer to the thermal characteristic graphs on Page 4 for selecting the
appropriate PCB copper area.
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BCR420UW6 / BCR421UW6
Application Information (Cont.)
PWM dimming can be achieved by driving the EN pin. Dimming is achieved by turning the LEDs ON and OFF for a portion of a single cycle. The
PWM signal can be provided by a micro-controller or analog circuitry; typical circuit is shown in Figure 3. Figure 4 is a typical response of LED
current vs. PWM duty cycle on the EN pin. PWM up to 25kHz with duty cycle of 0.5% (dimming range 200:1). This is above the audio band
minimizing audible power supply noise.
REXT
(Optional)
Figure 3 Application Circuits for LED Driver with PWM Dimming Functionality using BCR421U
Figure 4 Typical LED Current Response vs. PWM Duty Cycle for
25kHz PWM Frequency (Dimming Range 200:1)
BCR420UW6 / BCR421UW6
Document number: DS37667 Rev. 5 - 2
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BCR420UW6 / BCR421UW6
Application Information (Cont.)
To remove the potential of incorrect connection of the power supply
damaging the lamp’s LEDs, many systems use some form of
reverse polarity protection.
One solution for reverse input polarity protection is to simply use a
diode with a low VF in line with the driver/LED combination. The low
VF increases the available voltage to the LED stack and dissipates
less power. A circuit example is presented in Figure 5 which
protects the light engine although it will not function until the problem
is diagnosed and corrected. An SDM10U45LP (0.1A/45V) is shown,
providing exceptionally low VF for its package size of 1mm x 0.6mm.
Other reverse voltage ratings are available from Diodes
Incorporated’s website such as the SBR02U100LP (0.2A/100V) or
SBR0220LP (0.2A/20V).
While automotive applications commonly use this method for
reverse battery protection, an alternative approach shown in Figure
6, provides reverse polarity protection and corrects the reversed
polarity, allowing the light engine to function.
REXT
(Optional)
The BAS40BRW incorporates four low VF Schottky diodes in a
single package, reducing the power dissipated and maximizes the
voltage across the LED stack.
Figure 7 shows an example configuration for 350mA operation using
BCR421U. In such higher current configurations adequate enable
current is provided by increasing the enable voltage.
Figure 5 Application Circuit for LED Driver
with Reverse Polarity Protection
REXT
(Optional)
Figure 6 Application Circuit for LED Driver with
Assured Operation Regardless Of Polarity
BCR420UW6 / BCR421UW6
Document number: DS37667 Rev. 5 - 2
REXT =
2.1
Figure 7 Example for 350mA Operation using BCR421U
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BCR420UW6 / BCR421UW6
Package Outline Dimensions
Please see http://www.diodes.com/package-outlines.html for the latest version.
SOT26 (SC74R)
D
E1
SOT26 (SC74R)
Dim Min Max
Typ
A1 0.013 0.10
0.05
A2 1.00 1.30
1.10
A3 0.70 0.80
0.75
b
0.35 0.50
0.38
c
0.10 0.20
0.15
D
2.90 3.10
3.00
e
0.95
e1
1.90
E
2.70 3.00
2.80
E1 1.50 1.70
1.60
L
0.35 0.55
0.40
a
8°
a1
7°
All Dimensions in mm
E
b
a1
e1
A2
A3
A1
Seating Plane
e
L
c
a
Suggested Pad Layout
Please see http://www.diodes.com/package-outlines.html for the latest version.
SOT26 (SC74R)
C1
Y1
G
Dimensions Value (in mm)
C
2.40
C1
0.95
G
1.60
X
0.55
Y
0.80
Y1
3.20
C
Y
X
BCR420UW6 / BCR421UW6
Document number: DS37667 Rev. 5 - 2
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BCR420UW6 / BCR421UW6
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
(AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
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final and determinative format released by Diodes Incorporated.
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Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express
written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the
failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any
use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
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representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems.
Copyright © 2017, Diodes Incorporated
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BCR420UW6 / BCR421UW6
Document number: DS37667 Rev. 5 - 2
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