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General Description

The MAX6974/MAX6975 precision current-sinking,

24-output PWM LED drivers drive red, green, and blue

LEDs for full-color graphic message boards and video

displays. Each output has an individual 12-bit (MAX6974)

or 14-bit (MAX6975) PWM-intensity (hue) control and

7-bit (MAX6974) or 5-bit (MAX6975) global PWM intensity

(luminance) control. The MAX6974/MAX6975 feature a

high-speed, fully buffered cascadable serial interface,

open-circuit LED fault detection circuitry, as well as a

watchdog timer.

The driver has three banks of eight outputs, with each

bank intended to drive a different color in RGB applica-

tions. The full-scale current for each bank of eight out-

puts is adjustable from 6mA to 30mA in 256 steps

(0.3125% per step) to calibrate each color.

The MAX6974/MAX6975 can optionally multiplex by

using outputs MUX0 and MUX1, which each drive an

external pnp transistor. Multiplexing doubles the

MAX6974/MAX6975 drive capability to 48 LEDs.

The MAX6974/MAX6975 operate from a 3.0V to 3.6V

power supply. The LED power supply can range from

3V to 7V. The LED drivers require only 0.8V headroom

above the LEDs’ forward-voltage drop. Using a sepa-

rate LED supply voltage for each LED minimizes power

consumption.

The serial interface uses differential signaling for the

high-speed clock and data signals to reduce EMI and

improve signal integrity. The MAX6974/MAX6975 buffer

all interface signals to simplify cascading devices in

modules that use a large number of drivers.

An internal watchdog timer, when enabled, automatically

clears the pixel-data registers and blanks the display if

any of the signal inputs fail to toggle within 40ms.

The MAX6974/MAX6975 are available in 40-pin TQFN

packages and operate over the -40°C to +125°C

temperature range.

Refer to the MAX6972/MAX6973 data sheet for a

16-output, 11mA to 55mA software-compatible device.

Applications

LED Video Display Panels

LED Message Boards

Variable Message Signs (VMS)

Signs

Graphic Panels

Features

o 24 LED Current Sink Outputs (Three Banks of

Eight Outputs)

o 48 LED Drive Option When Multiplexing

o 33MHz Clock Supports Up to 63 Frames per

Second of Video

o Constant Output Current Calibration from 6mA to

30mA in 256 Steps

o EZCascade™ Interface Simplifies Multiple Driver

Cascading Without External Buffers

o 12-Bit or 14-Bit Individual PWM LED Intensity

Controls

o 7-Bit or 5-Bit Panel PWM-Intensity Control

o +3V to +7V LED Power Supply

o +3.0V to +3.6V Logic Supply

o Open-Circuit LED Fault Detection

o Optional Watchdog Timer Blanks Display if

Interface Fails

o Standard -40°C to +125°C Operating Temperature

Range

MAX6974/MAX6975

24-Output PWM LED Drivers

for Message Boards

________________________________________________________________

Maxim Integrated Products

19-0555; Rev 0; 5/06

For pricing delivery, and ordering information please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Typical Operating Circuit appears at the end of data sheet.

EP = Exposed pad.

Denotes lead-free package.

MAX6974ATL/

MAX6975ATL

TQFN-EP

TOP VIEW

4567

2728

EP*

*EP = EXPOSED PADDLE.

2930 26 24 23 22

8910

AGND

I.C.

LOADI

DIN-

DIN+

CLKI-

CLKI+

MUX0

CLKO+

CLK0-

DOUT+

DOUT-

LOADO

MUX1

Pin Configuration

Ordering Information

PART

TEMP RANGE

PIN-

PACKAGE

PKG

CODE

MAX6974ATL+ -40°C to +125°C 40 TQFN-EP*

T4066-3

MAX6975ATL+ -40°C to +125°C 40 TQFN-EP*

T4066-3

EZCascade is a trademark of Maxim Integrated Products, Inc.

1 2 3 4 5 6 ... 22 23

Indice de contenidos

Pagina 1 - 24-Output PWM LED Drivers

General DescriptionThe MAX6974/MAX6975 precision current-sinking, 24-output PWM LED drivers drive red, green, and blueLEDs for full-color graphic mess

Pagina 2

MAX6974/MAX6975Individual PWM ControlThe MAX6974/MAX6975 further modulate the time thateach subframe is ON by a pulse-width modulation(PWM) value. Eac

Pagina 3

169DEC,setting the port output current level to 21.8mA.The global-intensity PDM value is set to 96DEC, producingan even distribution of ON subframes o

Pagina 4

MAX6974/MAX6975Multiplexed vs. Nonmultiplexed OperationThe MAX6974/MAX6975 can double the number ofLEDs driven from 24 to 48 through multiplexing. Whe

Pagina 5

Setting configuration bit D0 to 1 enables multiplexoperation. MUX0 and MUX1 alternate the LED anodedrive voltage between two sets of LEDs. The R, G,

Pagina 6

MAX6974/MAX6975CommandsThe MAX6974/MAX6975 have four commands used toload all operating mode and LED output current data.Each command is uniquely iden

Pagina 7

The global-intensity data is received in an intermediateregister and is applied to the outputs at subframe 0 andPWM clock 0.The MAX6974/MAX6975 have o

Pagina 8

MAX6974/MAX6975The serial interface uses the continuously runningclock, CLKI, to synchronously transfer and latch data(33MHz max). The MAX6974/MAX6975

Pagina 9

segments transfer to all cascaded devices, while thedata section reduces in bit length as data transfersthrough the cascaded devices. When LOADI is lo

Pagina 10

MAX6974/MAX6975Data SegmentThe bit length of the data segment received by theMAX6974/MAX6975 is dependent on the commandspecified in the header.The lo

Pagina 11

Serial-Interface Cascade TimingThe MAX6974/MAX6975 serial-interface protocol timingis simplified by the guaranteed setup and hold charac-teristics of

Pagina 12

MAX6974/MAX697524-Output PWM LED Driversfor Message Boards2 _______________________________________________________________________________________ABS

Pagina 13

MAX6974/MAX6975When the MAX6974/MAX6975 send individual-intensityPWM data, the data segment bit length is large due tothe 12-bit or 14-bit PWM data fo

Pagina 14

MAX6974/MAX697524-Output PWM LED Driversfor Message Boards______________________________________________________________________________________ 21Use

Pagina 15

MAX6974/MAX697524-Output PWM LED Driversfor Message Boards22 ______________________________________________________________________________________Pac

Pagina 16

MAX6974/MAX697524-Output PWM LED Driversfor Message BoardsMaxim cannot assume responsibility for use of any circuitry other than circuitry entirely em

Pagina 17

MAX6974/MAX697524-Output PWM LED Driversfor Message Boards_______________________________________________________________________________________ 3Not

Pagina 18

MAX6974/MAX697524-Output PWM LED Driversfor Message Boards4 _______________________________________________________________________________________Typ

Pagina 19

MAX6974/MAX697524-Output PWM LED Driversfor Message Boards_______________________________________________________________________________________ 5Pin

Pagina 20

MAX6974/MAX697524-Output PWM LED Driversfor Message Boards6 _______________________________________________________________________________________MAX

Pagina 21

MAX6974/MAX697524-Output PWM LED Driversfor Message Boards_______________________________________________________________________________________ 7MAX

Pagina 22

MAX6974/MAX6975Detailed DescriptionThe MAX6974/MAX6975 drive 24 nonmultiplexed LEDsor 48 multiplexed LEDs for various indoor and outdoordisplay applic

Pagina 23

LED-Intensity ControlThe MAX6974/MAX6975 provide three levels of outputcurrent control for LED drive: calibration DACs(CALDACs), global-intensity cont

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