Embed Size (px)
Citation preview
Overview
• BCR42xU Introduction
• SOT26 (SC74) Family
• Target Applications
• Cross Reference
• Solution Comparison
• BCR42xU Application Notes
BCR42xU: Linear CCR for LED Driving
BCR420U & BCR421U are constant current regulators (CCR) for driving low power
LED strings by using NPN Emitter-Follower with Emitter Resistor to Current Limit.
10mA to 350mA
Adjustable CCR enables platform designs based on a single device to used across
multiple LED strip applications – easing manufacturer’s overall qualification process.
Increased Reliability
Monolithically integrating a transistor, diodes and resistors both simplifies the system by
reducing component count and increases overall reliability.
1.4 to 40V Supply Voltage
Low voltage overhead with sufficient headroom for over-voltage conditions such as
LEDs failing short.
Negative Temperature Coefficient
Self-protects and allows current sharing between parallel CCRs.
BCR421U with PWM
Enable function that can adjust the light output level by PWM up to 10kHz.
The Diodes Advantage
Part Number Config PWM
from µC
Input
Voltage
Fixed
Current
Adjustable
Current
Package
BCR420U NPN Low-side No 1.4 to 40V 10mA 10 to 350mA SOT26 (SC74)
BCR421U NPN Low-side Yes 1.4 to 40V 10mA 10 to 350mA SOT26 (SC74)
Compliance
Qualified to AEC-Q101 Standards for
High Reliability
BCR42xU: SOT26 Family
4
Part
Number Config
PWM
from
uC
Max.
Input
Voltage
Fixed
Current
Adjustable
Current Package Planned Release
BCR420U NPN Low-side No 40V 10mA 10 to 350mA SOT26 (SC74) Released
BCR421U NPN Low-side Yes 40V 10mA 10 to 350mA SOT26 (SC74) Released
BCR320U NPN Low-side No 25V 10mA 10 to 250mA SOT26 (SC74) BCR420U is alternative
BCR321U NPN Low-side Yes 25V 10mA 10 to 250mA SOT26 (SC74) BCR421U is alternative
• BCR420/1 Released, in production and samples available
• BCR320/1 are low voltage grades of the BCR420/1. Diodes Inc alternative is BCR420/1.
Design Registerable!
BCR42xU: Target Applications
Applications
Low power LED strip lighting:
Mood lighting
Emergency lighting strips
Medical lighting
Aircraft, train, ship illumination
Retrofits for general lighting
Advertising signage
Channel lighting
Retail refrigeration
Vending machines
Architectural lighting strips
BCR42xU: Cross Reference
Diodes Inc
Orderable
Part Number
Infineon
Orderable
Part Number
Infineon
Orderable
Part Number (*)
Package
BCR420U BCR420UW6-7 BCR420UE6327HTSA1 BCR320UE6327HTSA1 SOT26 (SC74)
BCR421U BCR421UW6-7 BCR421UE6327HTSA1 BCR321UE6327HTSA1 SOT26 (SC74)
* BCR320U & 321U are low voltage versions of the BCR420U & 421U.
Direct Equivalent to Infineon: Package, electrical & thermal performance, characterization
Design Registerable like INF
BCR42xU: Linear CCR for LED Driving
Linear Constant Current Regulators (CCR)
Emitter-follower with emitter resistor to current limit
• NPN low-side
• 10mA fixed current with internal resistor (95Ω)
• 10 to 350mA adjustable current with external resistor (REXT)
• Minimum output voltage, VOUT = 1.4V
• BCR421U can be PWM toggled via the enable (EN) pin
• SOT26 package with PD about 1W for linear mode power
dissipation
Consideration of the Linear mode PD needs to be factored
into the design – see Datasheet Application Information section. BCR420/1: Typical Application Circuit for Linear
Mode Current Sink LED Driver
BCR4xxU: Solution Comparison
BCRxx vs
Resistor BCRxx vs
Discrete BCRxx vs
AL5802 BCRxx vs
AL5809
BCRxx vs
Switch Mode
LED drivers
Homogenous output
LED current
independent of supply
voltage variations.
Parallel LED strings
Independently sets the
current in parallel LED
Longer LED lifetime
NTC reduces output
current with raising
temperature.
Single part
Increased reliability:
• Less soldering
points
• Reduced
components
• Reduced assembly
costs
• Smaller footprint
Designed and tested
as a linear LED driver
Monolithic
Increased reliability:
• Less die and bond
wires.
10 to 350mA
AL5802 = 1 to 120mA
40V max
AL5802 = 30V
1.4V min overhead
AL5809 = 2.5V
Adjustable CCR
Eases manufacturer’s
qual process –
Enables platform
designs based on a
single device
No EMI
Operating in linear
mode eliminates EMI.
Resistor Advantage
• Cost
• Smaller footprint
• Less components
Discrete Advantage
• Optimize the design
AL5802 Advantage
• 0.8V min overhead
• Lower min current
AL5809 Advantage
• Accuracy over
temperature
• Smaller footprint
• Less components
Switch Mode
Advantage
• Efficiency
BCR42xU: Setting the Current
BCR421U Output Current with different resistors BCR420U Output Current with different resistors
BCR42xU at 10mA nominal current. Adding in external resistor adjusts current as follows:
BCR42xU: Increasing Output Current
BCR420/1: Circuit for Increasing LED Current.
Increase LED String Current:
Negative temperature coefficient, reduces output current as the
temperature increases, without the risk of thermal runaway and
therefore they self-protect. This allows current sharing between
multiple BCR420/1 devices:
• Connect two or more BCR420/1s in Parallel.
• Consideration of the linear mode power dissipation
with appropriate thermal relief (PCB heat sinking)
• See Datasheet Application Information section.
BCR421U: PWM Dimming Circuit
Adjust LED Light Output Level
The low-side configuration allows the enable (EN) pin on the
BCR421U to be easily toggled and light output level adjusted:
• Dimming is achieved by turning the LEDs ON and OFF for a
portion of a single cycle
• BCR421U can be PWM dimmed with up to 10kHz signal from
microcontroller (µC) or analog circuit.
BCR421U PWM Dimming Function
Typical LED current
response vs PWM duty
cycle for 400Hz PWM
freq.
BCR421U: Other Circuits
350mA Current Output and Reverse Polarity Protection.
BCR421U operating up to 350mA
Adequate enable (EN) current into the base
is provided by increasing the EN voltage
BCR42xU with reverse polarity protection
Linear LED Driver: Support Tools
SPICE models:
Go to http://www.diodes.com/downloads/9271
Excel Calculator :
• Go to www.diodes.com
• Search for BCR4 parts
Samples:
• Go to www.diodes.com
• Search for BCR4 parts
• Buy Now from Authorized Distributor
