Information

10 Automotive Capabilities
Automotive Ambient Lighting Module
Reference Design (
APGRD004)
The Automotive Ambient Interior
Lighting Module Reference Design
demonstrates microcontroller-based
control of RGB LED devices. This
module can be controlled remotely
by a master body controller via a LIN bus. These
modules are offered in a very compact form-factor
board and are comprised of a PIC12F615 MCU, an
MCP2021 LIN transceiver/voltage regulator, and RGB
LED. LIN commands are interpreted by the module
to control color mixing (16,383 colors) and intensity
(1023 levels). The kit ships with 4modules to assign
as lighting zones in a LIN or J2602 network. These
modules can also be used in conjunction with the
APGDT001 LIN Serial Analyzer to quickly create a
working LIN network straight out of the box.
Enabling LED Lighting Applications
With the advances in
technology, LED lighting is
being used in both interior
and exterior applications
within the vehicle. LEDs
deliver long life, durability
and efficiency. For example
in a practical exterlor lighting application such as daytime
running lights, LED based daytime running lights improve
road safety and reduce fuel consumption by approximately
0.2 liter/100 km when compared to using the head lamp
operating in low beam mode. Plus LED daytime running
lamps offer the vehicles a touch of individual styling.
Effi cient LED Control
LEDs must be driven with a source of constant current.
Most LEDs have a specifi ed current level that will achieve
the maximum brightness for that LED without premature
failures. An LED could be driven with a linear voltage
regulator confi gured as a constant current source.
However, this approach is not practical for higher power
LEDs due to power dissipation in the regulator circuit. A
switch-mode power supply (SMPS) provides a much more
effi cient solution to drive the LED. SMPS implementation
with Microchip products can be analog, digital or mixed
signal based solutions.
An LED will have a forward voltage drop across its
terminals for a given current drive level. The power supply
voltage and the LED forward voltage characteristics
determine the SMPS topology that is required. Multiple
LEDs can be connected in series to increase the forward
voltage drop at the chosen drive current level.
The SMPS circuit topologies adopted to regulate current
in LED lighting applications are the same used to control
voltage in a power supply application. Each type of SMPS
topology offers the system designer trade-offs as shown
in the table below.
R BG
PIC12
Family
ADC Input
Color Set
RGB LED
50 mA
9-13V DC
User
Interface
LED Application Using PIC MCUs
Common SMPS Topologies Useful for LED Lighting
Regulator
Topology
VIN to VOUT
Relationship
Complexity
Component
Count
Comments
Charge Pump -VOUT < VIN < VOUT Low Medium
Limited IOUT range
No inductors
Buck VIN > VOUT Medium Medium
Chopped IIN
High side drive
Boost VIN < VOUT Medium Medium Extra parts needed to isolate output from input
SEPIC VOUT < VIN < VOUT Medium High
Smooth I
IN
Multiple outputs
Two inductors
Buck-Boost VOUT < VIN < VOUT Medium Medium
Single inductor
Up to four switches
Flyback
Depends on
transformer
Medium Medium
Transformer can provide electrical isolation
Multiple outputs possible
www.microchip.com/lighting