APGRD004 Microchip Technology, APGRD004 Datasheet - Page 12

• Manufacturer Part Number: APGRD004
• Description: REF DESIGN MOD AUTO AMBNT LIGHT
• Manufacturer: Microchip Technology

Specifications of APGRD004

• Main Purpose: Lighting, RGB LED Controller
• Embedded: Yes, MCU, 8-Bit
• Utilized Ic / Part: MCP2021, PIC12F615
• Primary Attributes: 4 Tiny Boards, Each Have: RGB LED, LIN Transceiver, Voltage Regulator, MCU
• Secondary Attributes: LIN Commands are Interpreted to Control 16,383 Colors and 1,023 Dimming Levels
• Silicon Manufacturer: Microchip
• Silicon Core Number: APGDT001
• Kit Contents: 4 Ambient Lighting Modules, Documentation
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Digital Control vs. Analog Control
LEDs can be driven with a fully digital control loop. Instead
of measuring the LED current with an op amp or comparator
circuit, the LED current is sampled using an ADC. Some
type of digital algorithm replaces the analog control loop.
A proportional-integral-derivative (PID) control algorithm is
commonly used because it has software coefficients that
can readily be adjusted to affect the controller behavior. A
digital PWM peripheral is used to drive the LED. The digital
algorithm computes an output based on its inputs and
provides the duty cycle for the PWM peripheral.
Literature on the Web
■
PIC12HV615 Buck LED Driver with Digital Control
Comparison of Digital Control vs. Analog Control Functions
12
LED Lighting Solutions
AN1138 – A Digital Constant Current Power LED Driver,
DS01138
LED Lighting Solutions Design Guide
Other Device Options:
PIC12F1822
PIC16F1823
Set Point
Analog Controller
+
–
Set
DC Bus
ADC Input
Controller
Output
Feedback
5V
Controller
PIC12HV615
Current
Sense
Filter
Feedback
Set Point
125 KHz
PWM
Low Cost Digital Control
Some power supply applications require fast dynamic
response to compensate for load changes. In these
applications, a fast ADC and fast calculation performance
are required. However, a LED provides a stable load for a
constant-current power supply. Therefore, a fast ADC and fast
processing power are not always required to implement a
digital control loop for a LED driver application.
A low-cost device in the PIC12F or PIC16F family with a CCP
peripheral and an ADC can be used to implement a LED
driver using digital control. The CCP peripheral is used in
PWM mode to control the power supply circuit. Operating
from the internal 8 MHz device oscillator, the CCP can
provide PWM frequencies above 100 KHz to keep power
component sizes small. Since the LED provides a constant
load, it is sufficient to sample the output current and adjust
the PWM duty cycle at a much lower rate. A sample rate of
1000 Hz is ideal for many applications.
ADC
Gate Driver
MCP1402
Digital Controller
Feedback Loop
Microcontroller
Digital Filter
Algorithm
PID or
15V
PWM
Controller
Output
www.microchip.com/lighting
LED
String