Rainbow Electronics MAX6973 - Manual (Page 8)

MAX6972/MAX6973
Detailed Description
The MAX6972/MAX6973 drive 16 nonmultiplexed LEDs
or 32 multiplexed LEDs for various indoor and outdoor
display applications. The EZCascade serial interface
enables large multidriver display panels to be con-
structed with interconnected MAX6972/MAX6973
devices (see Figure 1).
The drivers provide 12-bit (MAX6972) or 14-bit
(MAX6973) 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 MAX6972/MAX6973 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 (Y and Z) with eight
LED outputs per port. Each port features its own cur-
rent calibration control DAC (CALDAC) with 0.31%
resolution to set the current. The MAX6972/MAX6973 cur-
rent calibration feature allows unmatched LEDS from dif-
ferent lots and manufacturers to be color matched.
Power-Up
On power-up, the MAX6972/MAX6973 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.
16-Output PWM LED Drivers
for Message Boards
8 _______________________________________________________________________________________
HOST
CLKO
DOUT
LOADO
CLKI
DIN
LOADI
MAX6972/
MAX6973
1
MAX6972/
MAX6973
2
MAX6972/
MAX6973
3
MAX6972/
MAX6973
N
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
MAX6972 7 bits 6 bits 12 bits
5 bits 4 bits
MAX6973
16
(7V rated)
55mA 11mA to 55mA
3 bits 2 bits
14 bits
Table 1. Comparison of MAX6972/MAX6973