MAX6957 MAXIM [Maxim Integrated Products], MAX6957 Datasheet - Page 5

• Manufacturer Part Number: MAX6957
• Description: 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and 28-Port LED Display Driver and I/O Expander
• Manufacturer: MAXIM [Maxim Integrated Products]

The MAX6957 LED driver/GPIO peripheral provides up
to 28 I/O ports, P4 to P31, controlled through an SPI-
compatible serial interface. The ports can be config-
ured to any combination of constant-current LED
drivers, logic inputs and logic outputs, and default to
logic inputs on power-up. When fully configured as an
LED driver, the MAX6957 controls up to 28 LED seg-
ments with individual 16-step adjustment of the con-
stant current through each LED segment. A single
resistor sets the maximum segment current for all seg-
ments, with a maximum of 24mA per segment. The
MAX6957 drives any combination of discrete LEDs and
CA digits, including seven-segment and starburst
alphanumeric types.
Figure 1 is the MAX6957 functional diagram. Any I/O
port can be configured as a push-pull output (sinking
10mA, sourcing 4.5mA), or a Schmitt-trigger logic
input. Each input has an individually selectable internal
pullup resistor. Additionally, transition detection allows
seven ports (P24 through P30) to be monitored in any
maskable combination for changes in their logic status.
A detected transition is flagged through a status regis-
ter bit, as well as an interrupt pin (port P31), if desired.
The Typical Operating Circuit shows two MAX6957s
working together controlling three monocolor 16-seg-
ment-plus-DP displays, with five ports left available for
GPIO (P27–P31 of U2).
SSOP
5–24
DIP
2, 3
—
25
26
27
28
1
4
28-Port LED Display Driver and I/O Expander
PIN
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
SSOP
5–32
2, 3
—
33
34
35
36
1
4
_______________________________________________________________________________________
Detailed Description
P12–P31
P4–P31
NAME
DOUT
SCLK
GND
ISET
DIN
CS
V+
Segment Current Setting. Connect ISET to GND through a resistor (R
maximum segment current.
Ground
4-Wire Serial Data Output Port
LED Segment Drivers and GPIO. P12 to P31 can be configured as CA LED drivers, GPIO
outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.
LED Segment Drivers and GPIO. P4 to P31 can be configured as CA LED drivers, GPIO
outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.
4-Wire Serial Clock Input Port
4-Wire Serial Data Input Port
4-Wire Chip-Select Input, Active Low
Positive Supply Voltage. Bypass V+ to GND with a minimum 0.047µF capacitor.
The port configuration registers set the 28 ports, P4 to
P31, individually as either LED drivers or GPIO. A pair
of bits in registers 0x09 through 0x0F sets each port’s
configuration (Tables 1 and 2).
The 36-pin MAX6957AAX has 28 ports, P4 to P31. The
28-pin MAX6957ANI and MAX6957AAI only use 20 out-
puts, P12 to P31. The eight unused ports should be
configured as outputs on power-up by writing 0x55 to
registers 0x09 and 0x0A. If this is not done, the eight
unused ports remain as floating inputs and quiescent
supply current rises, although there is no damage to
the part.
The MAX6957 offers 20 or 28 I/O ports, depending on
package choice. These can be applied to a variety of
combinations of different display types, for example:
seven, 7-segment digits (Figure 2). This example
requires two MAX6957s, with one digit being driven by
both devices, half by one MAX6957, half by the other
(digit 4 in this example). The two drivers are static, and
therefore do not need to be synchronized. The
MAX6957 sees CA digits as multiple discrete LEDs. To
simplify access to displays that overlap two MAX6957s,
the MAX6957 provides four virtual ports P0 through P3.
To update an overlapping digit, send the same code
twice as an eight-port write, once to P28 through P35 of
the first driver, and again to P0 through P7 of the sec-
Register Control of I/O Ports and LEDs
FUNCTION
Across Multiple Drivers
Pin Description
ISET
) to set the
5