Datasheet

Detailed Description
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 configured
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 segments with individual
16-step adjustment of the constant current through each
LED segment. A single resistor sets the maximum seg-
ment current for all segments, 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 (sink-
ing 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 an interrupt pin
(port P31).
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).
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 make only 20
ports available. The eight unused ports should be con-
figured as outputs on power-up by writing 0x55 to reg-
isters 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.
PIN
NAME FUNCTION
28 SSOP
28 PDIP
36 SSOP 40 TQFN
1 1 36 ISET
Segment Current Setting. Connect ISET to GND through a resistor (R
ISET
) to set
the maximum segment current.
2, 3 2, 3
37, 38,
39
GND Ground
4 4 40 DOUT 4-Wire Serial Data Output Port
5–24 — — P12–P31
LED Segment Drivers and GPIO. P12 to P31 can be congured as CA LED drivers,
GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.
— 5–32
1–10,
12–19,
21–30
P4–P31
LED Segment Drivers and GPIO. P4 to P31 can be congured as CA LED drivers,
GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.
25 33 32 SCLK 4-Wire Serial Clock Input Port
26 34 33 DIN 4-Wire Serial Data Input Port
27 35 34 CS 4-Wire Chip-Select Input, Active-Low
28 36 35 V+ Positive Supply Voltage. Bypass V+ to GND with a minimum 0.047µF capacitor.
— —
11, 20,
31
N.C. No Connection. Not internally connected.
— — EP EP
Exposed Pad. Internally connected to GND. Connect to large ground plane for
maximum thermal dissipation. Do not use as sole ground connection.
www.maximintegrated.com
Maxim Integrated │ 5
MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Pin Description