AN2141 Datasheet, PDF (1/18 Pages) Panasonic Semiconductor – Video Camera Luminance Signal Processing Circuit

AN2141
Application note
LED array reference design board
Introduction
New high brightness LED (HB LED) applications such as displays, information panels,
signs, traffic signals, automotive lighting and advertising are becoming more and more
popular. For these applications new HB LED drivers with constant current outputs have
been designed. The constant LED current guarantees the same brightness for all LEDs and
provides a cost advantage in lighting system solutions, as there is no need for external
resistors for each individual LED. This document describes a simple design solution to drive
an array of high brightness LEDs, using the STP16CP05 and the STP16CPS05 LED
drivers.
Two reference design (one with 80 LEDs and another with 32 LEDs) are proposed to
provide a solution for driving high brightness LED arrays. The first has an array of 80 blue
HB LEDs arranged in a 5 x 16 matrix. This matrix of LEDs is driven by five 16-channel
STP16CPS05 drivers, with which it is possible to implement short, moving text. Also, all of
the LEDs in the display can be turned on simultaneously using a switch, in order to
demonstrate the uniformity in the brightness of the LEDs, which is achieved by applying the
same sink current to all channels. The second reference design is a smaller 4 x 8 LED
matrix driven by the STP16CP05 and the STP16CPS05, and includes a DC-DC converter
for supply voltages varying from 5 V up to 35 V. For this new 32 LED array reference design,
an evaluation board using OSRAM LEDs is available through order code STEVAL-
ILL003V2.
The new STP16CP05, STP08CP05 and STP16CPS05 LED drivers are monolithic, low
voltage 8-bit or 16-bit shift registers designed for driving LED and LED panel displays.
Thanks to these drivers the output LED current is constant and can be very precisely set
using just one external resistor to control the light intensity of the LEDs. The STPxxCx05
guarantees up to 20 V output driving capability, allowing designers to connect more LEDs in
series. The high 30 MHz clock frequency also satisfies the system requirement of high
volume data transmission. Both designs are controlled by the ST7Lite09 microcontroller,
which provides full text motion control, brightness regulation through PWM and control of
text speed. A 3.3 V supply voltage for the microcontroller and the drivers is provided by a
linear voltage regulator (the LE33 or L78L33).
The STP16CPS05 LED driver employs auto power saving to reduce power consumption.
January 2008
Rev 3
1/18
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