FreescaleRS08KA高亮LED解决方案

Freescale公司的MC9RS08KA2系列微控制器是超低成本低引脚数器件，特别适合家用电器，玩具和小型设备的应用。创新的高亮LED解决方案在低成本应用中迅速增长，但是低端高亮LED解决方案需要高级的系统控制和大恒流电流来维持色彩完整性和高的亮度输出。本文介绍采用MC9RS08KA2的主要性能，以及用MC9RS08KA2控制的高亮LED解决方案的电路图。

Innovative HBLED solutions are rapidly gaining popularity in low-cost applications
that require an extremely cost-effective bill-of-materials. However, low-end HBLED
applications still require a high level of system control as well as high constant-current to
maintain color integrity and high light output.
Freescale’s general-purpose ultra-low-end KA2 8-bit MCU offers an economical solution for this application. The on-chip analog comparator is designed to provide an accurate current measurement, which allows feedback control to maintain a constant level in the LED forward current.


MC9RS08KA2 Controlled High-Brightness LED



The MC9RS08KA2 Series microcontroller unit (MCU) is an extremely low-cost, small pin count device for home appliances, toys, and small geometry applications. This device is composed of standard on-chip modules including, a very small and highly efficient RS08 CPU core, 63 bytes RAM, 2K bytes Flash, an 8-bit modulo timer, keyboard interrupt, and analog comparator. The device is available in small 6- and 8-pin packages.



图1。MC9RS08KA2系列方框图

MC9RS08KA2主要特性：
8-Bit RS08 Central Processor Unit (CPU)
Simplified S08 instruction set with added high-performance instructions
LDA, STA, and CLR instructions support the short addressing mode; address $0000 to $001F can be accessed via a single-byte instruction
ADD, SUB, INC, and DEC instructions support the tiny addressing mode;
address $0000 to $000F can be accessed via a single-byte instruction with reduced instruction cycle
Shadow PC register instructions: SHA and SLA
Pending interrupt indication
Index addressing via D[X] and X register
Direct page access to the entire memory map through paging window
Memory
On-chip Flash EEPROM
MC9RS08KA2: 2048 bytes
MC9RS08KA1: 1024 bytes
63 bytes on-chip RAM
Power-Saving Modes
Wait and stop
Wakeup from power-saving modes using real-time interrupt (RTI), KBI, or ACMP
Clock Source
ICS — Trimmable 20-MHz internal clock source
Up to 10-MHz internal bus operation
0.2% trimmable resolution, 2% deviation over temperature and voltage range
System Protection
Computer operating properly (COP) reset running off bus-independent clock source
Low-voltage detection with reset or stop wakeup
Peripherals
MTIM — 8-bit modulo timer
ACMP — Analog comparator
Full rail-to-rail supply operation
Option to compare to fixed internal bandgap reference voltage
Can operate in stop mode
KBI — Keyboard interrupt ports
Three KBI ports in 6-pin package
Five KBI ports in 8-pin package
Development Support
Background debug system
Breakpoint capability to allow single breakpoint setting during in-circuit debug
Package Options
6-pin dual flat no lead (DFN) package
Two general-purpose input/output (I/O)pins
One general-purpose input pin
One general-purpose output pin
8-pin plastic dual in-line pin (PDIP) package
Four general-purpose input/output (I/O) pins
One general-purpose input pin
One general-purpose output pin
8-pin narrow body SOIC package
Four general-purpose input/output (I/O) pins
One general-purpose input pin
One general-purpose output pin


Innovative HBLED solutions are rapidly gaining popularity in low-cost applications
that require an extremely cost-effective bill-of-materials. However, low-end HBLED
applications still require a high level of system control as well as high constant-current to
maintain color integrity and high light output.
Freescale’s general-purpose ultra-low-end KA2 8-bit MCU offers an economical solution for this application. The on-chip analog comparator is designed to provide an accurate current measurement, which allows feedback control to maintain a constant level in the LED forward current.

KA2 HBLED Demo
Freescale demonstrates its ability to control the HBLED with a KA2 demo unit based on
a buck topology switching power supply.

This maximizes energy transfer between the battery and the HBLED. The KA2 microcontroller is used to measure the current through its on-chip analog comparator, then uses that feedback to control luminosity intensity on the LED. The user can toggle
between two MCU-controlled potential divider settings to vary the LED brightness levels. The demo unit also includes an open-source BDM interface for easy firmware evaluation.

下图是MC9RS08KA2控制的高亮LED电路图。