MAX6974 查看數據表（PDF） - Maxim Integrated

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MAX6974

24-Output PWM LED Drivers for Message Boards

Maxim Integrated 

24-Output PWM LED Drivers

for Message Boards

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.

HOST

CLKO

DOUT

LOADO

MAX6974/

MAX6975

1

CLKI

CLKO

DIN

DOUT

LOADI

LOADO

MAX6974/

MAX6975

2

CLKI

CLKO

DIN

DOUT

LOADI

LOADO

MAX6974/

MAX6975

3

CLKI

CLKO

DIN

DOUT

LOADI

LOADO

MAX6974/

MAX6975

N

CLKI

CLKO

DIN

DOUT

LOADI

LOADO

LOADI

DIN

CLKI

Figure 1. Generic Cascaded Connection Scheme

OPTIONAL FEEDBACK

Table 1. Comparison of MAX6974/MAX6975

PART

MAX6974

MAX6975

LED DRIVE

OUTPUTS

24

(7V rated)

LED DRIVE CALIBRATION

CURRENT DAC RANGE

30mA

6mA to 30mA

GLOBAL PDM

DIRECT

MULTIPLEXED

7 bits

6 bits

5 bits

4 bits

3 bits

2 bits

INDIVIDUAL

PWM

12 bits

14 bits

8 _______________________________________________________________________________________

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