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MAX6974/MAX6975

Detailed Description

The MAX6974/MAX6975 drive 24 nonmultiplexed LEDs

or 48 multiplexed LEDs for various indoor and outdoor

display applications. The EZCascade serial interface

enables large multidriver display panels to be con-

structed with interconnected MAX6974/MAX6975

devices (see Figure 1).

The drivers provide 12-bit (MAX6974) or 14-bit

(MAX6975) individual PWM steps for each LED output.

Four to seven global-intensity bits provide additional

pulse-density modulation (PDM) intensity control (see

Table 1). The MAX6974/MAX6975 provide 19 bits of

total current/intensity control range per color per pixel,

or 18 bits if multiplexing. The total PWM dynamic range

encompasses gamma correction and, if desired, indi-

vidual LED calibration.

LED outputs are grouped in ports (R, G, and B) with

eight LED outputs per port. Each port features its own

current calibration control DAC (CALDAC) with 0.31%

resolution to set the current. The MAX6974/

MAX6975 current calibration feature allows unmatched

LEDS from different lots and manufacturers to be

color matched.

Power-Up

On power-up, the MAX6974/MAX6975 set the calibration

current to the minimum current for all LED outputs and

clear the global-intensity PDM data, individual-intensity

PWM data, and the timing counters. The display

remains blank after CLKI starts running. The watchdog

function is inactive after power-up.

24-Output PWM LED Drivers

for Message Boards

8 _______________________________________________________________________________________

HOST

CLKO

DOUT

LOADO

CLKI

DIN

LOADI

MAX6974/

MAX6975

MAX6974/

MAX6975

MAX6974/

MAX6975

MAX6974/

MAX6975

CLKI

DIN

LOADI

CLKO

DOUT

LOADO

CLKI

DIN

LOADI

CLKO

DOUT

LOADO

CLKI

DIN

LOADI

CLKO

DOUT

LOADO

CLKI

DIN

LOADI

CLKO

DOUT

LOADO

OPTIONAL FEEDBACK

Figure 1. Generic Cascaded Connection Scheme

GLOBAL PDM

PART

LED DRIVE

OUTPUTS

LED DRIVE

CURRENT

CALIBRATION

DAC RANGE

DIRECT MULTIPLEXED

INDIVIDUAL

PWM

MAX6974 7 bits 6 bits 12 bits

5 bits 4 bits

MAX6975

(7V rated)

30mA 6mA to 30mA

3 bits 2 bits

14 bits

Table 1. Comparison of MAX6974/MAX6975

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 22 23

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