MCP1650 datasheet(12/20 Pages) MICROCHIP

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LED Lighting Solutions Design Guide

www.microchip.com/lighting

LED Lighting Solutions

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.

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

■ AN1138 – A Digital Constant Current Power LED Driver,

DS01138

Set Point

Feedback

Controller

Output

Microcontroller

Feedback

Controller

Output

Digital Controller

Feedback Loop

Set

Set Point

Analog Controller

ADC

PWM

PID or

Digital Filter

Algorithm

Controller

–

Comparison of Digital Control vs. Analog Control Functions

PIC12HV615 Buck LED Driver with Digital Control

LED

String

15V

Current

Sense

Filter

ADC Input

DC Bus

125 KHz

PWM

PIC12HV615

MCP1402

Gate Driver

Other Device Options:

PIC12F1822

PIC16F1823

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