MAX6960–MAX6963
4-Wire Serially Interfaced
8 x 8 Matrix Graphic LED Drivers
7
Maxim Integrated
• Bicolor: Literally means two color, and usually refers
to LEDs built with two LED dice of different colors,
typically red and green or red and orange/yellow.
• Tricolor: Literally means three color, and can refer to
LEDs built with three LED dice of different colors, typi-
cally red, green, and blue. The term is also used to
refer to a display built with bicolor LEDs, because there
are three main colors available (red, green, yellow).
• RGY: Display uses one red LED (R) and one green
LED (G) per pixel. When both red and green LEDs
are lit, the resulting color is yellow (Y). Varying the
current through the LEDs changes the intensity of the
pixel and changes the color from red through shades
of orange and yellow to green.
• RGB: Display uses one red LED (R), one green LED
(G), and one blue LED (B) per pixel. Varying the cur-
rent through the LEDs changes the intensity of the
pixel and changes the color through many shades
limited by the current control resolution.
MAX6960 Applications
The MAX6960 is a multiplexed, constant-current LED
driver intended for high-efficiency indoor signage and
message boards.
The high efficiency arises because the driver operates
from a 3.3V nominal supply with minimal voltage head-
room required across the driver output stages. The
problem of removing heat from even a small display is
therefore minimized.
The maximum peak LED drive current is 40mA, which
when multiplexed eight ways, provides an average cur-
rent of 5mA per LED. This current drive is expected to
be adequate for indoor applications, but inadequate for
outdoor signs operating in direct sun.
The MAX6960 directly drives monocolor (typically red
or orange/yellow) or RGY (typically red/green or
red/yellow) graphic displays using LEDs with a forward
voltage drop up to 2.5V. Blue LEDs and some green
LEDs cannot be driven directly because of their high
forward voltage drop (around 3.5V to 4.5V). For these
displays, the MAX6960 can be used as a graphic con-
troller, just as it can be used for applications requiring
higher peak segment currents, and in RGB panels
needing a higher driver voltage for the blue LEDs. In
these cases, the MAX6960 can be used with external
drive transistors to control anode-row displays, with all
driver features including pixel-level intensity control still
available (see the
Applications Information
section and
Figure 17).
Display Intensity Control
Five levels of intensity control are provided:
• A 256-step PWM panel intensity adjustment sets all
MAX6960s simultaneously as a global panel bright-
ness control (Table 27). The 256-step resolution is
fine enough to allow fade-in/fade-out graphic effects,
as well as provide a means for compensating a
panel for background lighting.
• A 2-bits-per-pixel intensity control allows four bright-
ness levels to be set independently per pixel. The
pixel-level intensity control can be set to be either
arithmetic (off, 1/3, 2/3, full) or geometric (off, 1/4,
1/2, full) for full flexibility (Table 24), and allows four
colors to be displayed on monocolor panels, or 16
colors to be displayed on RGY panels, or 64 colors
to be displayed on RGB panels.
• The LED drive current can be selected between
either a 40mA peak per segment and a lower 20mA
peak current on a digit-by-digit basis using the
R
ISET0
and R
ISET1
pins. The lower (20mA) current
may be the better choice to drive high-efficiency dis-
plays, and this setting allows the MAX6960 to oper-
ate from a supply voltage as low as 2.7V.
• The LED drive current can be adjusted between
40mA and 20mA peak current on a digit-by-digit
basis using fixed or adjustable resistors connected
from the R
ISET0
and R
ISET1
pins to GND. These con-
trols enable analog relative adjustments in digit
intensity, typically to calibrate digits from different
batches, or to color balance RGY displays.
• The digit intensity controls allow each digit’s operat-
ing current to be scaled down in 256 steps from the
global panel intensity adjustment. The effective oper-
ating current for each digit becomes n/256th of the
panel intensity value. These controls enable digital
relative adjustments in digit intensity in addition to
the analog approach outlined above.
Display Size Limitations
The maximum display size that can be handled by a
single 4-wire serial interface is given in Table 2, which
is for the maximum 256 interconnected MAX6960s.
Larger display panels can be designed using a sepa-
rate CS line for each group of (up to) 256 MAX6960s.
Each group would also have its own local 3-wire bus to
allocate the driver addresses. The 4-wire interface
speeds requirement when continuously updating dis-
play memory for high-speed animations is given in
Table 3.
