AN2415
Application note
Using the output detection feature of the high-brightness
LED driver STP08CDC596 evaluation board
Introduction
This document describes how to implement a complete solution for driving a high-brightness
LED array. Based on STP08CDC596 drivers and controlled by an ST7FLITE3x
microcontroller, there are two versions of the evaluation board:
■
■
STEVAL-ILL002V1 using OSRAM LEDs
STEVAL-ILL002V2 using Toshiba LEDs
Note:
The STP08CDC596 LED driver is replaced by the new, higher performing STP08DP05 LED
driver. The two available versions of the evaluation board with the STP08DP05 replace the
STEVAL-ILL002V1 and the STEVAL-ILL002V2, and are described in application note
AN2478.
The new boards available are:
■
■
STEVAL-ILL002V3 using OSRAM LEDs
STEVAL-ILL002V4 using VISHAY LEDs
Forty high-brightness LEDs are arranged on the board in a 5x8 matrix. The matrix is driven
by five 8-channel STP08CDC596 drivers.
The main features of the evaluation board are:
■
■
■
■
■
Brightness and blinking regulation
Animated text
Error detection on output
GUI (graphic user interface)
DC-DC converter
The innovative feature of the STP08CDC596 is the full output error detection function which
enables output status checking without invasive testing (via software only).
Figure 1.
STEVAL-ILL002Vx evaluation board
For more information about other boards based on the STPxxC/L596 driver family, refer to
application note AN2141 which provides details concerning the basic features of the driver
family, the microcontroller interface and chip power dissipation. Refer to user manual
UM0181 for information about how to get started using the evaluation boards.
August 2007
Rev 4
1/11
www.st.com
Contents
AN2415
Contents
1
2
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Operation mode switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1
2.2
Normal mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Error detection mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3
Firmware implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1
3.2
3.3
Timing diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Option byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
GUI features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2/11
AN2415
List of figures
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
STEVAL-ILL002Vx evaluation board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
STEVAL-ILL002Vx evaluation board block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Error Detection mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Normal mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Timing diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
MCU option bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
LED matrix board application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3/11
Overview
AN2415
1
Overview
The STEVAL-ILL002Vx evaluation board can be powered with voltages from 7 V up to 32 V.
The SMPS DC-DC converter block is based on the L5970D step-down switching regulator
and the DC-DC block is based on the LE50ABD voltage regulator. The power topology
makes it possible to power the board using a laptop power supply.
Figure 2
shows the block diagram of the evaluation board.
Figure 2.
STEVAL-ILL002Vx evaluation board block diagram
SMPS
DC/DC
Power Supply
DC/DC
LED Matrix
…
…
Control Panel
LED Driver
8-bit µC
SPI
SPI
… .
…
RS232 Driver
The brain of the board is the 8-bit ST7FLITE39 microcontroller. It receives inputs from the
control panel, sends and receives data from the LED drivers through the serial peripheral
interface (SPI) and enables PC communication through the serial communications interface
(SCI). The control panel consists of switches, potentiometers and jumpers. Switches are
used to reset the microcontroller and to enter Detection mode. Potentiometers change the
brightness and text speed. Jumpers are used to simulate errors (open and short circuit) on
the LED matrix.
A LED matrix consists of 40 LEDs arranged in a 5x8 matrix. A dedicated PC GUI displays
the status of the LEDS.
4/11
AN2415
Operation mode switching
2
Operation mode switching
To enter Error Detection or Normal mode, the drivers must receive a particular sequence on
the OE and LE pins.
When a one-clock-wide short pulse “101” is sent on the OE pin, the drivers enter the
switching phase. If the LE pin is sampled as high voltage at the 4th rising edge of CLK, the
drivers switch to Error Detection mode (Figure
3).
Otherwise, they switch to Normal mode
(Figure
4).
Note:
In the firmware, with SW2 pressure only the drivers enter Error Detection mode, and after an
error detection check, they re-enter Normal mode.
Figure 3.
Error Detection mode
Figure 4.
Normal mode
2.1
Normal mode
In Normal mode, the serial data is transferred from the microcontroller to the drivers via the
SPI. The serial data from microcontroller is sent to the drivers via the SDI pin, undergoes a
shift in the Shift Register, and exits via the SDO pin. The LE pin can latch the serial data in
the Shift Register to the output latch. The OE pin enables the output driver sink current.
Current is modulated by the potentiometer, which changes the PWM duty cycle on the OE
pin (PWM frequency is set at 244 Hz).
5/11
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