MAX6975 Maxim Integrated Products, MAX6975 Datasheet - Page 8

• Manufacturer Part Number: MAX6975
• Description: (MAX6974 / MAX6975) 24-Output PWM LED Drivers
• Manufacturer: Maxim Integrated Products

24-Output PWM LED Drivers
for Message Boards
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
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
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.
Figure 1. Generic Cascaded Connection Scheme
Table 1. Comparison of MAX6974/MAX6975
8
MAX6974
MAX6975
_______________________________________________________________________________________
PART
1). The MAX6974/MAX6975 provide 19 bits of
HOST
LOADO
LOADI
DOUT
CLKO
CLKI
DIN
Figure
LED DRIVE
OUTPUTS
(7V rated)
1).
CLKI
DIN
LOADI
24
Detailed Description
MAX6974/
MAX6975
1
LOADO
DOUT
CLKO
LED DRIVE
CURRENT
30mA
CLKI
DIN
LOADI
MAX6974/
MAX6975
2
CALIBRATION
DAC RANGE
6mA to 30mA
LOADO
DOUT
CLKO
OPTIONAL FEEDBACK
CLKI
DIN
LOADI
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.
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.
MAX6974/
MAX6975
3
DIRECT
LOADO
7 bits
5 bits
3 bits
CLKO
DOUT
GLOBAL PDM
MULTIPLEXED
6 bits
4 bits
2 bits
CLKI
DIN
LOADI
MAX6974/
MAX6975
N
LOADO
CLKO
DOUT
INDIVIDUAL
Power-Up
12 bits
14 bits
PWM