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MAX6955

2-Wire Interfaced, 2.7V to 5.5V LED Display Driver with I/O Expander and Key Scan

Maxim Integrated 

MAX6955

2-Wire Interfaced, 2.7V to 5.5V

LED Display Driver with I/O

Expander and Key Scan

Pin Description

PIN

SSOP TQFN-EP

1, 2,

34, 35

36, 37,

33, 34

NAME

P0–P3

FUNCTION

General-Purpose I/O Ports (GPIOs). GPIO can be configured as logic inputs or open-drain

outputs. Enabling key scanning configures some or all ports P0–P3 as key-switch matrix inputs

with internal pullup (Key_A through Key_D).

3

38

AD0

Address Input 0. Sets device slave address. Connect to GND, V+, SCL, or SDA to give four

logic combinations. See Table 5.

4

39

SDA I2C-Compatible Serial Data I/O

5

40

SCL I2C-Compatible Serial Clock Input

6

1

AD1

Address Input 1. Sets device slave address. Connect to GND, V+, SCL, or SDA to give four

logic combinations. See Table 5.

7–15,

22–31

2–10,

21–30

O0–O18

Digit/Segment Drivers. When acting as digit drivers, outputs O0 to O7 sink current from the

display common cathodes. When acting as segment drivers, O0 to O18 source current to the

display anodes. O0 to O18 are high impedance when not being used as digit or segment

drivers.

16, 18 12, 13, 15 GND Ground

17

14

ISET

Segment Current Setting. Connect ISET to GND through series resistor RSET to set the peak

current.

19, 21 16, 18, 19

V+

Positive Supply Voltage. Bypass V+ to GND with a 47µF bulk capacitor and a 0.1µF ceramic

capacitor.

20

17

OSC

Multiplex Clock Input. To use internal oscillator, connect capacitor CSET from OSC to GND.

To use external clock, drive OSC with a 1MHz to 8MHz CMOS clock.

32

31

BLINK Blink Clock Output. Output is open drain.

33

32

OSC_OUT

Clock Output. OSC_OUT is a buffered clock output to allow easy blink synchronization of

multiple MAX6955s. Output is push-pull.

36

35

P4/IRQ General-Purpose I/O Port. Also functions as IRQ output when key scanning is enabled.

—

11, 20

N.C. Not Internally Connected

—

—

EP

Exposed Paddle. Internally connected to GND. Connect to a large ground plane to improve

thermal performance.

Detailed Description

The MAX6955 is a serially interfaced display driver that

can drive up to 16 digits 7-segment, 8 digits 14-seg-

ment, 8 digits 16-segment, 128 discrete LEDs, or a

combination of these display types. Table 1 shows the

drive capability of the MAX6955 for monocolor and

bicolor displays.

The MAX6955 includes 104-character ASCII font maps

for 14-segment and 16-segment displays, as well as

the hexadecimal font map for 7-segment displays. The

characters follow the standard ASCII font, with the

addition of the following common symbols: £, €, ¥, °, µ,

±, ↑, and ↓. Seven bits represent the 104-character

font map; an 8th bit is used to select whether the deci-

mal point (DP) is lit. Seven-segment LED digits can be

controlled directly or use the hexadecimal font. Direct

segment control allows the MAX6955 to be used to

drive bar graphs and discrete LED indicators.

Tables 2, 3, and 4 list the connection schemes for 16-,

14-, and 7-segment digits, respectively. The letters in

Tables 2, 3, and 4 correspond to the segment labels

shown in Figure 1. (For applications that require mixed

display types, see Tables 38–41.)

Serial Interface

Serial Addressing

The MAX6955 operates as a slave that sends and

receives data through an I2C-compatible 2-wire inter-

face. The interface uses a serial data line (SDA) and a

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