MAX6960–MAX6963
4-Wire Serially Interfaced
8 x 8 Matrix Graphic LED Drivers
29
Maxim Integrated
Power Supplies
The MAX6960 operates from a single 2.7V to 3.6V
power supply. Accuracy of the LED drive current of
20mA is guaranteed over this supply range. Accuracy
of the LED drive current of 40mA is guaranteed over a
supply range of 3.15V to 3.6V.
Bypass each of the 5 V+ power-supply pins to GND
with a 0.1µF capacitor as close to the device as possi-
ble. Add a 10µF to 100µF bulk decoupling capacitor to
the supply bus at least every several MAX6960s. Each
MAX6960 draws a peak current of either 40mA x 16
segments = 640mA (current setting = high) or 20mA x
16 segments = 320mA (current setting = low), regard-
less of the PWM plane and pixel intensity settings. If
ripple sync and/or mux flip are enabled, then the timing
of these peak currents is desynchronized between dri-
vers, providing an easier load to the power supply. For
all but the smallest display panels, it is necessary to
use 2oz copper boards to minimize the voltage drops
across the supply planes with the high currents that are
required. Set the supply voltage to 3.6V at the panel
supply input to allow the most margin for on-board sup-
ply voltage drops. For the TQFN package, connect the
exposed pad to GND.
RST
Input
The external reset input, RST, is asserted low and halts
internal operations and forces control registers to their
default values shown in Table 12. In systems where the
MAX6960s are operated from different regulated sup-
plies with different power-up delays, hold RST of every
interconnected MAX6960 low until 50ms after the last
MAX6960 has powered up. RST can be asserted low at
any time to force all devices to the default condition. RST
must be driven by a CMOS logic output supplied by V+.
A supervisor, such as the MAX6821x526, which has an
adjustable power-up reset delay, is a good choice.
When RST is deasserted, the sequence of events for
writing global registers and auto-address configuration is
the same as described in the
Initial Power-Up
section.
Package Dissipation
Typical full-power (all segments on) device power dissi-
pation is 671mW (V+ = 3.3V, V
LED
= 2.3V, I
LED
=
40mA, 254/256 full intensity). Consider the effect of one
or more shorted display LEDs in planning dissipation
handling. The MAX6960 remains under the 1023mW
MQFP package dissipation limit at +70°C with V+ =
3.6V and V
LED
= 2.1V. The TQFN package is preferred
for 40mA segment current applications because the
2.16W package dissipation limit easily handles worst-
case applications including multiple shorted LEDs.
Connecting Multiple MAX6960s to
the 4-Wire Bus
Up to 256 MAX6960s can be interconnected to share
the same 4-wire bus in parallel, sharing a common CS.
The maximum of 256 devices is set by the automatic
address allocation limit. Care is needed to achieve the
successful parallel interconnection of more than 16
MAX6960s due to the high-capacitive loading this pre-
sents onto the 4-wire bus. It is generally necessary to
either buffer and drive the CLK, DIN, and CS lines to
small groups of drivers, or to reduce the 4-wire data
rate from the 20Mb/s limit, if more than approximately
16 MAX6960s are used. The exact limit depends on the
application’s 4-wire data rate requirement, the capaci-
tive drive capability of the host’s CLK, DIN, and CS dri-
vers, and the effective capacitance of the CLK, DIN,
and CS routing on the circuit board. The circuit in
Figure 15 shows one way of fanning out the CLK, DIN,
and CS lines to 128 MAX6960s, and fanning in the
DOUT lines back into one DOUT line. The CLK, DIN,
and CS lines are buffered with standard CMOS bus
buffers, with each buffer output driving 16 CLK, DIN, or
CS inputs. The tri-state DOUT outputs are also connect-
ed together in groups of 16, and fed into octal analog
multiplexers. The analog multiplexers are used here as
data selectors, with the very low (10Ω) switch resis-
tance providing an effective logic power driver. Note,
however, that while the MAX6960’s DOUT output is tri-
state, the selected DOUT from this power driver is not.
Using the MAX6960 as Controller for
Higher Voltage or Higher Current
The MAX6960 can be used as a graphic controller with
external drive transistors for applications requiring
higher peak segment currents and/or a higher drive
voltage (multiple LEDs in series for each pixel). The
panel and pixel-level intensity control is still available
because PWM techniques are used, but the peak seg-
ment current is set by external current-limiting resistors
in series with the LEDs, instead of the MAX6960’s inter-
nal precision constant-current sources. Figure 16
shows example output drivers that interface the
MAX6960 to control anode-row displays at a higher
segment current and drive voltage. Sixteen instances of
the low-current cathode column driver, and eight
instances of the high-current anode row driver are
required per MAX6960.
