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General Description
The MAX6955 is a compact display driver that interfaces
microprocessors to a mix of 7-segment, 14-segment,
and 16-segment LED displays through an I
2
CTM-compati-
ble 2-wire serial interface. The MAX6955 drives up to 16
digits 7-segment, 8 digits 14-segment, 8 digits 16-seg-
ment, or 128 discrete LEDs, while functioning from a
supply voltage as low as 2.7V. The driver includes five
I/O expander or general-purpose I/O (GPIO) lines, some
or all of which can be configured as a key-switch reader.
The key-switch reader automatically scans and
debounces a matrix of up to 32 switches.
Included on chip are full 14- and 16-segment ASCII
104-character fonts, a hexadecimal font for 7-segment
displays, multiplex scan circuitry, anode and cathode
drivers, and static RAM that stores each digit. The max-
imum segment current for the display digits is set using
a single external resistor. Digit intensity can be inde-
pendently adjusted using the 16-step internal digital
brightness control. The MAX6955 includes a low-power
shutdown mode, a scan-limit register that allows the
user to display from 1 to 16 digits, segment blinking
(synchronized across multiple drivers, if desired), and a
test mode, which forces all LEDs on. The LED drivers
are slew-rate limited to reduce EMI.
For an SPITM-compatible version, refer to the MAX6954
data sheet. An evaluation kit* (EV kit) for the MAX6955
is available.
*Future product--contact factory for availability.
Applications
Set-Top Boxes
Automotive
Panel Meters
Bar Graph Displays
White Goods
Audio/Video Equipment
Features
o 400kbps 2-Wire Interface Compatible with I
2
C
o 2.7V to 5.5V Operation
o Drives Up to 16 Digits 7-Segment, 8 Digits
14-Segment, 8 Digits 16-Segment, 128 Discrete
LEDs, or a Combination of Digit Types
o Drives Common-Cathode Monocolor and Bicolor
LED Displays
o Built-In ASCII 104-Character Font for 14-Segment
and 16-Segment Digits and Hexadecimal Font for
7-Segment Digits
o Automatic Blinking Control for Each Segment
o 10A (typ) Low-Power Shutdown (Data Retained)
o 16-Step Digit-by-Digit Digital Brightness Control
o Display Blanked on Power-Up
o Slew-Rate-Limited Segment Drivers for Lower EMI
o Five GPIO Port Pins Can Be Configured as Key-
Switch Reader to Scan and Debounce Up to 32
Switches with n-Key Rollover
o IRQ Output when a Key Input is Debounced
o 36-Pin SSOP and 40-Pin DIP Packages
o Automotive Temperature Range Standard
MAX6955
2-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan
________________________________________________________________ Maxim Integrated Products
1
Ordering Information
19-2548; Rev 0; 7/02
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
PART
TEMP RANGE
PIN-PACKAGE
MAX6955AAX
-40C to +125C
36 SSOP
MAX6955APL
-40C to +125C
40 PDIP
I
2
C is a trademark of Philips Corp.
SPI is a trademark of Motorola, Inc.
Pin Configurations and Typical Operating Circuits appear
at end of data sheet.
ISET
OSC
OSC_OUT
BLINK
SCL
AD0
AD1
SDA
2-WIRE SERIAL INTERFACE
RAM
BLINK
CONTROL
CONFIGURATION
REGISTER
CHARACTER
GENERATOR
ROM
CURRENT
SOURCE
DIVIDER/
COUNTER
NETWORK
DIGIT
MULTIPLEXER
PWM
BRIGHTNESS
CONTROL
GPIO
AND KEY-SCAN
CONTROL
LED
DRIVERS
O0 TO O18
P0 TO P4
MAX6955
Functional Diagram
EVALUATION KIT
AVAILABLE
MAX6955
2-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage (with Respect to GND)
V+ .........................................................................-0.3V to +6V
SCL, SDA, AD0, AD1 ...........................................-0.3V to +6V
All Other Pins............................................-0.3V to (V+ + 0.3V)
Current
O0O7 Sink Current ......................................................935mA
O0O18 Source Current .................................................55mA
SCL, SDA, AD0, AD1, BLINK, OSC, OSC_OUT, ISET ....20mA
P0, P1, P2, P3, P4 ...........................................................40mA
GND .....................................................................................1A
Continuous Power Dissipation (T
A
= +70C)
36-Pin SSOP (derate at 11.8mW/C above +70C) .....941mW
40-Pin PDIP (derate at 16.7mW/C above +70C).....1333mW
Operating Temperature Range
(T
MIN
to T
MAX
) ...............................................-40C to +125C
Junction Temperature ......................................................+150C
Storage Temperature Range .............................-65C to +150C
Lead Temperature (soldering, 10s) .................................+300C
DC ELECTRICAL CHARACTERISTICS
(Typical Operating Circuit, V+ = 2.7V to 5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Operating Supply Voltage
V+
2.7
5.5
V
T
A
= +25C
10
35
Shutdown Supply Current
I
SHDN
Shutdown mode, all
digital inputs at V+
or GND
T
A
= T
MIN
to T
MAX
40
A
T
A
= +25C
22
30
Operating Supply Current
I+
All segments on, all
digits scanned,
intensity set to full,
internal oscillator, no
display or OSC_OUT
load connected
T
A
= T
MIN
to T
MAX
35
mA
OSC = RC oscillator, R
SET
= 56k
,
C
SET
= 22pF, V+ = 3.3V
4
Master Clock Frequency
f
OSC
OSC driven externally
1
8
MHz
Dead Clock Protection Frequency
f
OSC
95
kHz
OSC Internal/External Detection
Threshold
V
OSC
1.7
V
OSC High Time
t
CH
50
ns
OSC Low Time
t
CL
50
ns
Slow Segment Blink Period
f
SLOWBLINK
OSC = RC oscillator, R
SET
= 56k
,
C
SET
= 22pF, V+ = 3.3V
1
s
Fast Segment Blink Period
f
FASTBLINK
OSC = RC oscillator, R
SET
= 56k
,
C
SET
= 22pF, V+ = 3.3V
0.5
s
Fast or Slow Segment Blink Duty
Cycle
49.5
50.5
%
MAX6955
2-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan
_______________________________________________________________________________________
3
DC ELECTRICAL CHARACTERISTICS (continued)
(Typical Operating Circuit, V+ = 2.7V to 5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
LED
= 2.2V,
V+
= 3.3V
Segment Drive Source Current
I
SEG
V
LED
= 2.2V,
V+
= 2.7V
T
A
= +25C
-32
-40
-48
mA
Segment Current Slew Rate
I
SEG
/
t
T
A
= +25C, V+ = 3.3V
11
mA/s
Segment Drive Current Matching
I
SEG
T
A
= +25C, V+ = 3.3V
5
%
LOGIC INPUTS AND OUTPUTS
Input High Voltage
SDA, SCL, AD0, AD1
V
IH
0.7 x
V+
V
Input Low Voltage
SDA, SCL, AD0, AD1
V
IL
0.3 x
V+
V
Input Leakage Current
SDA, SCL, AD0, AD1, OSC, P0,
P1, P2, P3, P4
I
IH
, I
IL
-1
+1
A
SDA Output Low Voltage
V
OLSDA
I
SINK
= 6mA
0.4
V
Port Logic-High Input Voltage
P0, P1, P2, P3, P4
V
IHP
0.7 x
V+
V
Port Logic-Low Input Voltage
P0, P1, P2, P3, P4
V
ILP
0.3 x
V+
V
Port Hysteresis Voltage
P0, P1, P2, P3, P4
V
IP
0.03 x
V+
V
Port Input Pullup Current from V+
I
IPU
P0 to P3 configured as key-scan inputs,
V+ = 3.3V
75
A
Port Output Low Voltage
V
OLP
I
SINK
= 8mA
0.3
0.5
V
Blink Output Low Voltage
V
OLBK
I
SINK
= 0.6mA
0.1
0.3
V
OSC_OUT Output High Voltage
V
OHOSC
I
SOURCE
= 1.6mA
V+ -
0.4
V
OSC_OUT Output Low Voltage
V
OLOSC
I
SINK
= 1.6mA
0.4
V
MAX6955
2-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan
4
_______________________________________________________________________________________
TIMING CHARACTERISTICS
(Typical Operating Circuit, V+ = 2.7V to 5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
TIMING CHARACTERISTICS
Serial Clock Frequency
f
SCL
400
kHz
Bus Free Time Between a STOP
and a START Condition
t
BUF
1.3
s
Hold Time (Repeated) START
Condition
t
HD,
t
STA
0.6
s
Repeated START Condition Setup
Time
t
SU
, t
STA
0.6
s
STOP Condition Setup Time
t
SU:STO
0.6
s
Data Hold Time
t
HD
, t
DAT
(Note 3)
0.9
s
Data Setup Time
t
SU
, t
DAT
100
ns
SCL Clock Low Period
t
LOW
1.3
s
SCL Clock High Period
t
HIGH
0.6
s
Rise Time of Both SDA and SCL
Signals, Receiving
t
R
(Notes 2, 4)
20 +
0.1C
B
300
ns
Fall Time of Both SDA and SCL
Signals, Receiving
t
F
(Notes 2, 4)
20 +
0.1C
B
300
ns
Fall Time of SDA Transmitting
t
F
, t
X
(Notes 2, 5)
20 +
0.1C
B
300
ns
Pulse Width of Spike Suppressed
t
SP
(Notes 2, 6)
0
50
ns
Capacitive Load for Each
Bus Line
C
B
(Note 2)
400
pF
Note 1: All parameters tested at T
A
= +25C. Specifications over temperature are guaranteed by design.
Note 2: Guaranteed by design.
Note 3: A master device must provide a hold time of at least 300ns for the SDA signal (referred to V
IL
- of the SCL signal) in order to
bridge the undefined region of SCL's falling edge.
Note 4: C
B
= total capacitance of one bus line in pF. t
R
and t
F
measured between 0.3V+ and 0.7V+.
Note 5: I
SINK
6mA. C
B
= total capacitance of one bus line in pF. t
R
and t
F
measured between 0.3V+ and 0.7V+.
Note 6: Input filters on the SDA and SCL inputs suppress noise spikes less than 50ns.
MAX6955
2-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan
_______________________________________________________________________________________
5
Typical Operating Characteristics
(V+ = 3.3V, LED forward voltage = 2.4V, Typical Application Circuit, T
A
= +25C, unless otherwise noted.)
INTERNAL OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX6955 toc01
TEMPERATURE (
C)
OSCILLATOR FREQUENCY (MHz)
110
80
50
20
-10
3.8
4.0
4.2
4.4
3.6
-40
R
SET
= 56k
C
SET
= 22pF
SUPPLY VOLTAGE (V)
5.0
4.5
4.0
3.5
3.0
2.5
5.5
INTERNAL OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
MAX6955 toc02
OSCILLATOR FREQUENCY (MHz)
3.8
4.0
4.2
4.4
3.6
R
SET
= 56k
C
SET
= 22pF
100ns/div
OSC: 500mV/div
OSC_OUT: 2V/div
MAX6954 toc03
OSC
0V
0V
OSC_OUT
INTERNAL OSCILLATOR WAVEFORM
AT OSC AND OSC_OUT PINS
R
SET
= 56k
C
SET
= 22pF
DEAD CLOCK OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
85
90
95
100
105
110
80
SUPPLY VOLTAGE (V)
5.0
4.5
4.0
3.5
3.0
2.5
5.5
MAX6955 toc04
OSCILLATOR FREQUENCY (MHz)
R
SET
= 56k
C
SET
= GND
CURRENT NORMALIZED TO 40mA 0.94
0.96
0.98
1.00
1.02
0.92
SEGMENT SOURCE CURRENT
vs. SUPPLY VOLTAGE
SUPPLY VOLTAGE (V)
5.0
4.5
4.0
3.5
3.0
2.5
5.5
MAX6955 toc05
V
LED
= 1.8V
1V/div
200
s/div
MAX6954 toc06
O0
O18
WAVEFORM AT PINS O0 AND O18,
MAXIMUM INTENSITY
0V
0V
GPIO SINK CURRENT
vs. TEMPERATURE
MAX
6955 toc07
TEMPERATURE (
C)
GPIO SINK CURRENT (mA)
110
80
50
20
-10
5
10
15
20
25
30
35
40
45
0
-40
V
CC
= 5.5V
V
CC
= 3.3V
V
CC
= 2.5V
OUTPUT = LOW
V
PORT
= 0.6V
PORT INPUT PULLUP CURRENT
vs. TEMPERATURE
MAX6955 toc08
TEMPERATURE (
C)
KEY-SCAN SOURCE CURRENT (mA)
110
80
50
20
-10
0.1
0.2
0.3
0.4
0.5
0
-40
V
CC
= 5.5V
V
CC
= 3.3V
V
CC
= 2.5V
OUTPUT = HIGH
V
PORT
= 1.4V
400
s/div
KEY_A: 1V/div
IRQ: 2V/div
MAX6954 toc09
KEY_A
0V
0V
IRQ
KEY-SCAN OPERATION
(KEY_A AND IRQ)
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