General Description
The MAX6956 compact, serial-interfaced LED display
driver/I/O expander provide microprocessors with up to
28 ports. Each port is individually user configurable to
either a logic input, logic output, or common-anode
(CA) LED constant-current segment driver. Each port
configured as an LED segment driver behaves as a
digitally controlled constant-current sink, with 16 equal
current steps from 1.5mA to 24mA. The LED drivers are
suitable for both discrete LEDs and CA numeric and
alphanumeric LED digits.
Each port configured as a general-purpose I/O (GPIO)
can be either a push-pull logic output capable of sink-
ing 10mA and sourcing 4.5mA, or a Schmitt logic input
with optional internal pullup. Seven ports feature config-
urable transition detection logic, which generates an
interrupt upon change of port logic level. The MAX6956
is controlled through an I2C-compatible 2-wire serial
interface, and uses four-level logic to allow 16 I2C
addresses from only 2 select pins.
The MAX6956AAX and MAX6956ATL have 28 ports
and are available in 36-pin SSOP and 40-pin thin QFN
packages, respectively. The MAX6956AAI and
MAX6956ANI have 20 ports and are available in 28-pin
SSOP and 28-pin DIP packages, respectively.
For an SPI-interfaced version, refer to the MAX6957
data sheet. For a lower cost pin-compatible port
expander without the constant-current LED drive capa-
bility, refer to the MAX7300 data sheet.
Applications
Set-Top Boxes Bar Graph Displays
Panel Meters Industrial Controllers
White Goods System Monitoring
Automotive
Features
o400kbps I2C-Compatible Serial Interface
o2.5V to 5.5V Operation
o-40°C to +125°C Temperature Range
o20 or 28 I/O Ports, Each Configurable as
Constant-Current LED Driver
Push-Pull Logic Output
Schmitt Logic Input
Schmitt Logic Input with Internal Pullup
o11µA (max) Shutdown Current
o16-Step Individually Programmable Current
Control for Each LED
oLogic Transition Detection for Seven I/O Ports
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
________________________________________________________________
Maxim Integrated Products
1
28
27
26
25
24
23
22
21
20
19
18
17
16
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
V+
AD1
SCL
SDA
P31
P30
P22
P29
P28
P27
P26
P25
P24
P23
P21
P20
P19
P18
P17
P16
P15
P14
P13
P12
AD0
GND
GND
ISET
SSOP/DIP
TOP VIEW
MAX6956
Pin Configurations
19-2414; Rev 4; 6/10
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Typical Operating Circuit appears at end of data sheet.
Ordering Information
PART TEMP RANGE PIN-PACKAGE
MAX6956ANI+ -40°C to +125°C 28 DIP
MAX6956AAI+ -40°C to +125°C 28 SSOP
MAX6956AAX+ -40°C to +125°C 36 SSOP
MAX6956ATL+ -40°C to +125°C 40 Thin QFN-EP*
MAX6956AAX/V -40°C to +125°C 36 SSOP
MAX6956AAX/V+T -40°C to +125°C 36 SSOP
Pin Configurations continued at end of data sheet.
/V denotes an automotive qualified part.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
*
EP = Exposed pad.
EVALUATION KIT
AVAILABLE
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
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)
P4–P31 Current ................................................................±30mA
GND Current .....................................................................800mA
Continuous Power Dissipation
28-Pin PDIP (derate 14.3mW/°C above TA= +70°C) 1143mW
28-Pin SSOP (derate 9.1mW/°C above TA= +70°C)...727mW
36-Pin SSOP (derate 11.8mW/°C above TA= +70°C) ...941mW
40-Pin TQFN (derate 26.3mW/°C above TA= +70°C) 2105mW
Operating Temperature Range
(TMIN to TMAX) ...............................................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Soldering Temperature (reflow)
Lead(Pb)-free packages...............................................+260°C
Packages containing lead(Pb)......................................+240°C
ELECTRICAL CHARACTERISTICS
(
Typical Operating Circuit
, V+ = 2.5V to 5.5V, TA= TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Operating Supply Voltage V+ 2.5 5.5 V
TA = +25°C 5.5 8
TA = -40°C to +85°C 10
Shutdown Supply Current ISHDN All digital inputs at V+
or GND TA = TMIN to TMAX 11
µA
TA = +25°C 180 230
TA = -40°C to +85°C 250
Operating Supply Current IGPOH
All ports programmed
as outputs high, no
load, all other inputs at
V+ or GND TA = TMIN to TMAX 270
µA
TA = +25°C 170 210
TA = -40°C to +85°C 230
Operating Supply Current IGPOL
All ports programmed
as outputs low, no
load, all other inputs at
V+ or GND TA = TMIN to TMAX 240
µA
TA = +25°C 110 135
TA = -40°C to +85°C 140
Operating Supply Current ILED
Al l p or ts p r og r am m ed
as LE D outp uts, al l LE D s
off, no l oad , al l other
i np uts at V + or GN D TA = TMIN to TMAX 145
µA
INPUTS AND OUTPUTS
Logic-High Input Voltage
Port Inputs VIH 0.7 ✕
V+ V
Logic-Low Input Voltage
Port Inputs VIL 0.3 ✕
V+ V
Input Leakage Current IIH, IIL GPIO inputs without pullup,
VPORT = V+ to GND -100 ±1 +100 nA
V+ = 2.5V 12 19 30
GPIO Input Internal Pullup to V+ IPU V+ = 5.5V 80 120 180 µA
Hysteresis Voltage GPIO Inputs ∆VI0.3 V
GPIO outputs, ISOURCE = 2mA, TA = -40°C to
+85°C
V+ -
0.7
Output High Voltage VOH GPIO outputs, ISOURCE = 1mA, TA = TMIN to
TMAX (Note 2)
V+ -
0.7
V
Port Sink Current IOL VPORT = 0.6V 2 10 18 mA
Output Short-Circuit Current IOLSC Port configured output low, shorted to V+ 2.75 11 20 mA
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
_______________________________________________________________________________________ 3
Note 1: All parameters tested at TA= +25°C. 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 VIL of the SCL signal) in order to
bridge the undefined region of SCL’s falling edge.
Note 4: Cb= total capacitance of one bus line in pF. tRand tFmeasured between 0.3V+ and 0.7V+.
Note 5: ISINK ≤6mA. Cb= total capacitance of one bus line in pF. tRand tFmeasured between 0.3V+ and 0.7V+.
Note 6: Input filters on the SDA and SCL inputs suppress noise spikes less than 50ns.
ELECTRICAL CHARACTERISTICS (continued)
(
Typical Operating Circuit
, V+ = 2.5V to 5.5V, TA= TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
V+ = 2.5V, VLED = 2.3V at maximum LED
current 9.5 13.5 18
V+ = 3.3V, VLED = 2.4V at maximum LED
current (Note 2) 18.5 24 27.5
Port Drive LED Sink Current,
Port Configured as LED Driver IDIGIT
V+ = 5.5V, VLED = 2.4V at maximum LED
current 19 25 30
mA
V+ = 2.5V, VOUT = 0.6V at maximum sink
current 18.5 23 28
Port Drive Logic Sink Current,
Port Configured as LED Driver IDIGIT_SC V+ = 5.5V, VOUT = 0.6V at maximum sink
current 19 24 28
mA
Input High-Voltage SDA, SCL,
AD0, AD1 VIH 0.7 ✕
V+ V
Input Low-Voltage SDA, SCL,
AD0, AD1 VIL 0.3 ✕
V+ V
Input Leakage Current SDA, SCL IIH, IIL -50 50 nA
Input Capacitance (Note 2) 10 pF
Output Low-Voltage SDA VOL ISINK = 6mA 0.4 V
TIMING CHARACTERISTICS (Figure 2)
(V+ = 2.5V to 5.5V, TA= TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Serial Clock Frequency fSCL 400 kHz
Bus Free Time Between a STOP
and a START Condition tBUF 1.3 µs
Hold Time (Repeated) START
Condition tHD
,
STA 0.6 µs
Repeated START Condition
Setup Time tSU
,
STA 0.6 µs
STOP Condition Setup Time tSU
,
STO 0.6 µs
Data Hold Time tHD
,
DAT (Note 3) 15 900 ns
Data Setup Time tSU
,
DAT 100 ns
SCL Clock Low Period tLOW 1.3 µs
SCL Clock High Period tHIGH 0.7 µs
Rise Time of Both SDA and SCL
Signals, Receiving tR(Notes 2, 4) 20 +
0.1Cb300 ns
Fall Time of Both SDA and SCL
Signals, Receiving tF(Notes 2, 4) 20 +
0.1Cb300 ns
Fall Time of SDA Transmitting tF,TX (Notes 2, 5) 20 +
0.1Cb250 ns
Pulse Width of Spike Suppressed tSP (Notes 2, 6) 0 50 ns
Capacitive Load for Each Bus
Line Cb(Note 2) 400 pF
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
4 _______________________________________________________________________________________
OPERATING SUPPLY CURRENT
vs. TEMPERATURE
MAX6956 toc01
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
97.570.042.515.0-12.5
0.04
0.08
0.12
0.16
0.20
0.24
0.28
0.32
0.36
0.40
0
-40.0 125.0
V+ = 2.5V TO 5.5V
NO LOAD
ALL PORTS
OUTPUT (1)
ALL PORTS
OUTPUT (0)
ALL PORTS LED (OFF)
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX6956 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
97.570.042.515.0-12.5
4
5
6
7
8
3
-40.0 125.0
V+ = 5.5V
V+ = 3.3V
V+ = 2.5V
OPERATING SUPPLY CURRENT vs. V+
(NO LOADS)
MAX6956 toc03
V+ (V)
SUPPLY CURRENT (mA)
5.04.54.03.53.02.5
0.1
1
10
100
0.01
2.0 5.5
ALL PORTS LED (ON)
ALL PORTS LED (OFF)
ALL PORTS OUTPUT (1)
ALL PORTS OUTPUT (0)
LED DRIVER SINK CURRENT
vs. V+
MAX6956 toc04
V+ (V)
PORT SINK CURRENT (mA)
5.04.53.5 4.03.02.5
8
10
12
14
16
18
20
22
24
26
6
2.0 5.5
LED DROP = 2.4V
LED DROP = 1.8V
GPO SOURCE CURRENT vs. TEMPERATURE
(OUTPUT = 1)
MAX6956 toc07
TEMPERATURE (°C)
PORT SOURCE CURRENT (mA)
97.570.042.515.0-12.5
3
4
5
6
7
8
9
2
-40.0 125.0
VPORT = 1.4V
V+ = 5.5V
V+ = 3.3V
V+ = 2.5V
LED DRIVER SINK CURRENT
vs. TEMPERATURE
MAX6956 toc05
TEMPERATURE (°C)
PORT SINK CURRENT (mA)
97.570.042.515.0-12.5
21
22
23
24
25
26
27
20
-40.0 125.0
VLED = 2.4V
V+ = 5.5V
V+ = 3.3V
GPO SINK CURRENT vs. TEMPERATURE
(OUTPUT = 0)
MAX6956 toc06
TEMPERATURE (°C)
PORT SINK CURRENT (mA)
97.570.0-12.5 15.0 42.5
4
6
8
10
12
14
16
18
2
-40.0 125.0
V+ = 2.5V TO 5.5V, VPORT = 0.6V
GPI PULLUP CURRENT
vs. TEMPERATURE
MAX6956 toc08
TEMPERATURE (°C)
PULLUP CURRENT (µA)
97.570.042.515.0-12.5
100
1000
10
-40.0 125.0
V+ = 5.5V
V+ = 3.3V
V+ = 2.5V
GPO SHORT-CIRCUIT CURRENT
vs. TEMPERATURE
MAX6956 toc09
TEMPERATURE (°C)
PORT CURRENT (mA)
97.570.042.515.0-12.5
10
100
1
-40.0 125.0
GPO = 0, PORT
SHORTED TO V+
GPO = 1, PORT
SHORTED TO GND
__________________________________________Typical Operating Characteristics
(RISET = 39kΩ, TA = +25°C, unless otherwise noted.)
Detailed Description
The MAX6956 LED driver/GPIO peripheral provides up
to 28 I/O ports, P4 to P31, controlled through an I2C-com-
patible 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
MAX6956 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 MAX6956 drives any combination of
discrete LEDs and CA digits, including seven-segment
and starburst alphanumeric types.
Figure 1 is the MAX6956 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 mask-
able combination for changes in their logic status. A
detected transition is flagged through a status register
bit, as well as an interrupt pin (port P31), if desired.
The
Typical Operating Circuit
shows two MAX6956s
working together controlling three monocolor 16-seg-
ment-plus-DP displays, with five ports left available for
GPIO (P26–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 MAX6956AAX has 28 ports, P4 to P31. The
28-pin MAX6956ANI and MAX6956AAI make only 20
ports available, P12 to P31. The eight unused ports
should be configured as outputs on power-up by writ-
ing 0x55 to registers 0x09 and 0x0A. If this is not done,
the eight unused ports remain as unconnected inputs
and quiescent supply current rises, although there is no
damage to the part.
Register Control of I/O Ports and LEDs
Across Multiple Drivers
The MAX6956 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 7). This example
requires two MAX6956s, with one digit being driven by
both devices, half by one MAX6956, half by the other
(digit 4 in this example). The two drivers are static, and
therefore do not need to be synchronized. The
MAX6956 sees CA digits as multiple discrete LEDs. To
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
_______________________________________________________________________________________ 5
PIN
SSO P/D IP SSOP T Q F N NAME FUNCTION
1 1 36 ISET Segment Current Setting. Connect ISET to GND through a resistor (RISET) to set
the maximum segment current.
2, 3 2, 3 37, 38, 39 GND Ground
4 4 40 AD0 Address Input 0. Sets device slave address. Connect to either GND, V+, SCL,
SDA to give four logic combinations. See Table 3.
5–24 — — P 12–P 31
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.
— 5–32
1–10,
12–19,
21–30
P4–P31
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.
— — 11, 20, 31 N.C. No Connection
25 33 32 SDA I2C-Compatible Serial Data I/O
26 34 33 SCL I2C-Compatible Serial Clock Input
27 35 34 AD1 Address Input 1. Sets device slave address. Connect to either GND, V+, SCL,
SDA to give four logic combinations. See Table 3.
28 36 35 V+ Positive Supply Voltage. Bypass V+ to GND with minimum 0.047µF capacitor.
———EP
Exposed Pad (TQFN Only). Not internally connected. Connect EP to ground
plane for maximum thermal performance.
Pin Description
MAX6956
simplify access to displays that overlap two MAX6956s,
the MAX6956 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-
ond driver. The first driver ignores the last 4 bits and
the second driver ignores the first 4 bits.
Two addressing methods are available. Any single port
(bit) can be written (set/cleared) at once; or, any
sequence of eight ports can be written (set/cleared) in
any combination at once. There are no boundaries; it is
equally acceptable to write P0 through P7, P1 through
P8, or P31 through P38 (P32 through P38 are nonexis-
tent, so the instructions to these bits are ignored).
Using 8-bit control, a seven-segment digit with a deci-
mal point can be updated in a single byte-write, a 14-
segment digit with DP can be updated in two byte-
writes, and 16-segment digits with DP can be updated
in two byte-writes plus a bit write. Also, discrete LEDs
and GPIO port bits can be lit and controlled individually
without affecting other ports.
Shutdown
When the MAX6956 is in shutdown mode, all ports are
forced to inputs (which an be read), and the pullup cur-
rent sources are turned off. Data in the port and control
registers remain unaltered, so port configuration and
output levels are restored when the MAX6956 is taken
out of shutdown. The display driver can still be pro-
grammed while in shutdown mode. For minimum sup-
ply current in shutdown mode, logic inputs should be at
GND or V+ potential. Shutdown mode is exited by set-
ting the S bit in the configuration register (Table 8).
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
6 _______________________________________________________________________________________
Table 1. Port Configuration Map
REGISTER DATA
REGISTER ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
Port Configuration for P7, P6, P5, P4 0x09 P7 P6 P5 P4
Port Configuration for P11, P10, P9, P8 0x0A P11 P10 P9 P8
Port Configuration for P15, P14, P13, P12 0x0B P15 P14 P13 P12
Port Configuration for P19, P18, P17, P16 0x0C P19 P18 P17 P16
Port Configuration for P23, P22, P21, P20 0x0D P23 P22 P21 P20
Port Configuration for P27, P26, P25, P24 0x0E P27 P26 P25 P24
Port Configuration for P31, P30, P29, P28 0x0F P31 P30 P29 P28
Table 2. Port Configuration Matrix
Note: The logic is inverted between the two output modes; a high makes the output go low in LED segment driver mode (0x00) to
turn that segment on; in GPIO output mode (0x01), a high makes the output go high.
PORT
CONFIGURATION
BIT PAIR
MODE FUNCTION
PORT
REGISTER
(
0x20–0x5F
)
PIN BEHAVIOR ADDRESS
CODE
(
HEX
)
UPPER LOWER
Register bit = 0 High impedance
Output LED Segment Driver Register bit = 1
Open-drain current sink, with sink
current (up to 24mA) determined
by the appropriate current register
0x09 to 0x0F 0 0
Register bit = 0 Active-low logic output
Output GPIO Output Register bit = 1 Active-high logic output 0x09 to 0x0F 0 1
Input GPIO Input
Without Pullup Schmitt logic input 0x09 to 0x0F 1 0
Input GPIO Input with Pullup
Register bit =
input logic level Schmitt logic input with pullup 0x09 to 0x0F 1 1
Shutdown mode is temporarily overridden by the dis-
play test function.
Serial Interface
Serial Addressing
The MAX6956 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
serial clock line (SCL) to achieve bidirectional commu-
nication between master(s) and slave(s). A master (typ-
ically a microcontroller) initiates all data transfers to and
from the MAX6956, and generates the SCL clock that
synchronizes the data transfer (Figure 2).
The MAX6956 SDA line operates as both an input and
an open-drain output. A pullup resistor, typically 4.7kΩ,
is required on SDA. The MAX6956 SCL line operates
only as an input. A pullup resistor, typically 4.7kΩ, is
required on SCL if there are multiple masters on the 2-
wire interface, or if the master in a single-master system
has an open-drain SCL output.
Each transmission consists of a START condition
(Figure 3) sent by a master, followed by the MAX6956
7-bit slave address plus R/Wbit (Figure 6), a register
address byte, one or more data bytes, and finally a
STOP condition (Figure 3).
Start and Stop Conditions
Both SCL and SDA remain high when the interface is
not busy. A master signals the beginning of a transmis-
sion with a START (S) condition by transitioning SDA
from high to low while SCL is high. When the master
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
_______________________________________________________________________________________________________ 7
SLAVE ADDRESS BYTE
D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15
R/W
8
8
CEDATA
8
SDA
SCL
TEST REGISTER
INTENSITY REGISTERS
PORT REGISTERS
LED DRIVERS AND GPIO
INTENSITY
CONFIGURATION
TEST
P4 TO P31
LED DRIVERS
OR GPIO
ADDRESS
MATCHER
AD0
AD1
COMMAND BYTEDATA BYTE
R/W7-BIT DEVICE ADDRESS
7
7
TO COMMAND REGISTERS
TO/FROM DATA REGISTERS
SEGMENT OR
GPIO DATA R/W
CONFIGURATION
REGISTERS
PORT CHANGE
DETECTOR
MASK REGISTER
COMMAND
REGISTER DECODE
8
DATA BYTE COMMAND BYTE
MAX6956
Figure 1. MAX6956 Functional Diagram
MAX6956
has finished communicating with the slave, it issues a
STOP (P) condition by transitioning SDA from low to
high while SCL is high. The bus is then free for another
transmission (Figure 3).
Bit Transfer
One data bit is transferred during each clock pulse.
The data on SDA must remain stable while SCL is high
(Figure 4).
Acknowledge
The acknowledge bit is a clocked 9th bit, which the
recipient uses to handshake receipt of each byte of
data (Figure 5). Thus, each byte transferred effectively
requires 9 bits. The master generates the 9th clock
pulse, and the recipient pulls down SDA during the
acknowledge clock pulse, such that the SDA line is sta-
ble low during the high period of the clock pulse. When
the master is transmitting to the MAX6956, the
MAX6956 generates the acknowledge bit because the
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
8 _______________________________________________________________________________________
Figure 2. 2-Wire Serial Interface Timing Details
SCL
SDA
START CONDITIONSTOP CONDITION
REPEATED START CONDITION
START CONDITION
tSU, DAT
tHD, DAT
tLOW
tHD, STA
tHIGH
tRtF
tSU, STA
tHD, STA
tSU, STO
tBUF
Figure 3. Standard Stop Conditions
SDA
SCL S
START
CONDITION
P
STOP
CONDITION
SDA
SCL DATA LINE STABLE;
DATA VALID CHANGE OF DATA ALLOWED
Figure 4. Bit Transfer
MAX6956 is the recipient. When the MAX6956 is trans-
mitting to the master, the master generates the
acknowledge bit because the master is the recipient.
Slave Address
The MAX6956 has a 7-bit-long slave address (Figure 6).
The eighth bit following the 7-bit slave address is the
R/Wbit. It is low for a write command, high for a read
command.
The first 3 bits (MSBs) of the MAX6956 slave address
are always 100. Slave address bits A3, A2, A1, and A0
are selected by address inputs, AD1 and AD0. These
two input pins may be connected to GND, V+, SDA, or
SCL. The MAX6956 has 16 possible slave addresses
(Table 3) and therefore, a maximum of 16 MAX6956
devices may share the same interface.
Message Format for Writing
the MAX6956
A write to the MAX6956 comprises the transmission of
the MAX6956’s slave address with the R/Wbit set to
zero, followed by at least 1 byte of information. The first
byte of information is the command byte. The com-
mand byte determines which register of the MAX6956
is to be written by the next byte, if received. If a STOP
condition is detected after the command byte is
received, then the MAX6956 takes no further action
(Figure 8) beyond storing the command byte.
Any bytes received after the command byte are data
bytes. The first data byte goes into the internal register of
the MAX6956 selected by the command byte (Figure 9). If
multiple data bytes are transmitted before a STOP condi-
tion is detected, these bytes are generally stored in subse-
quent MAX6956 internal registers because the command
byte address generally autoincrements (Table 4).
Message Format for Reading
The MAX6956 is read using the MAX6956’s internally
stored command byte as address pointer, the same
way the stored command byte is used as address
pointer for a write. The pointer generally autoincre-
ments after each data byte is read using the same rules
as for a write (Table 4). Thus, a read is initiated by first
configuring the MAX6956’s command byte by perform-
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
_______________________________________________________________________________________ 9
SCL
SDA
BY TRANSMITTER
CLOCK PULSE FOR ACKNOWLEDGMENT
START CONDITION
SDA
BY RECEIVER
12 89
S
Figure 5. Acknowledge
SDA
SCL
1 0 A3 A2 A1 A00
MSB LSB
R/W ACK
Figure 6. Slave Address
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
10 ______________________________________________________________________________________
P0 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 P31
7-SEGMENT DIGIT 1
VIRTUAL SEGMENTS
VIRTUAL SEGMENTS
7-SEGMENT DIGIT 5 7-SEGMENT DIGIT 6 7-SEGMENT DIGIT 7
7-SEGMENT DIGIT 2 7-SEGMENT DIGIT 3 7-SEGMENT DIGIT 4 V+
V+
P0 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 P31
Figure 7. Two MAX6956s Controlling Seven 7-Segment Displays
SAAP0
SLAVE ADDRESS COMMAND BYTE
ACKNOWLEDGE FROM MAX6956
R/W ACKNOWLEDGE FROM MAX6956
D15 D14 D13 D12 D11 D10 D9 D8
COMMAND BYTE IS STORED ON RECEIPT OF STOP CONDITION
COMMAND BYTE RECEIVED
Figure 8. Command Byte Received
SAAAP0
SLAVE ADDRESS COMMAND BYTE DATA BYTE
ACKNOWLEDGE FROM MAX6956
1 BYTE
D15 D14 D13 D12 D11 D10 D9 D8 D1 D0D3 D2D5 D4D7 D6
HOW COMMAND BYTE AND DATA BYTE MAP INTO MAX6956's REGISTER
ACKNOWLEDGE FROM MAX6956 ACKNOWLEDGE FROM MAX6956
R/W
Figure 9. Command and Single Data Byte Received
ing a write (Figure 8). The master can now read n con-
secutive bytes from the MAX6956, with the first data
byte being read from the register addressed by the ini-
tialized command byte. When performing read-after-
write verification, remember to reset the command
byte’s address because the stored control byte
address generally has been autoincremented after the
write (Table 4). Table 5 is the register address map.
Operation with Multiple Masters
If the MAX6956 is operated on a 2-wire interface with
multiple masters, a master reading the MAX6956
should use a repeated start between the write, which
sets the MAX6956’s address pointer, and the read(s)
that takes the data from the location(s). This is because
it is possible for master 2 to take over the bus after
master 1 has set up the MAX6956’s address pointer but
before master 1 has read the data. If master 2 subse-
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 11
COMMAND BYTE ADDRESS RANGE AUTOINCREMENT BEHAVIOR
x0000000 to x1111110 Command address autoincrements after byte read or written
x1111111 Command address remains at x1111111 after byte written or read
PIN
CONNECTION DEVICE ADDRESS
AD1 AD0 A6 A5 A4 A3 A2 A1 A0
GND GND 1 0 0 0 0 0 0
GND V+ 1000001
GND SDA 1000010
GND SCL 1000011
V+ GND 1000100
V+ V+ 1000101
V+ SDA 1000110
V+ SCL 1000111
SDA GND 1001000
SDA V+ 1001001
SDA SDA 1 0 0 1 0 1 0
SDA SCL 1 0 0 1 0 1 1
SCL GND 1001100
SCL V+ 1001101
SCL SDA 1 0 0 1 1 1 0
SCL SCL 1 0 0 1 1 1 1
SA A AP0
SLAVE ADDRESS COMMAND BYTE DATA BYTE
ACKNOWLEDGE FROM MAX6956
D15 D14 D13 D12 D11 D10 D9 D8 D1 D0D3 D2D5 D4D7 D6
HOW COMMAND BYTE AND DATA BYTE MAP INTO MAX6956's REGISTER
ACKNOWLEDGE FROM MAX6956
R/W n BYTES
AUTOINCREMENT MEMORY WORD ADDRESS
ACKNOWLEDGE FROM MAX6956
Figure 10. n Data Bytes Received
Table 3. MAX6956 Address Map
Table 4. Autoincrement Rules
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
12 ______________________________________________________________________________________
Table 5. Register Address Map
COMMAND ADDRESS
REGISTER D15 D14 D13 D12 D11 D10 D9 D8
HEX
CODE
No-Op X 0 0 0 0 0 0 0 0x00
Global Current X 0 0 0 0 0 1 0 0x02
Configuration X 0 0 0 0 1 0 0 0x04
Transition Detect Mask X 0 0 0 0 1 1 0 0x06
Display Test X 0 0 0 0 1 1 1 0x07
Port Configuration P7, P6, P5, P4 X 0 0 0 1 0 0 1 0x09
Port Configuration P11, P10, P9, P8 X 0 0 0 1 0 1 0 0x0A
Port Configuration P15, P14, P13, P12 X 0 0 0 1 0 1 1 0x0B
Port Configuration P19, P18, P17, P16 X 0 0 0 1 1 0 0 0x0C
Port Configuration P23, P22, P21, P20 X 0 0 0 1 1 0 1 0x0D
Port Configuration P27, P26, P25, P24 X 0 0 0 1 1 1 0 0x0E
Port Configuration P31, P30, P29, P28 X 0 0 0 1 1 1 1 0x0F
Current054 X 0 0 1 0 0 1 0 0x12
Current076 X 0 0 1 0 0 1 1 0x13
Current098 X 0 0 1 0 1 0 0 0x14
Current0BA X 0 0 1 0 1 0 1 0x15
Current0DC X 0 0 1 0 1 1 0 0x16
Current0FE X 0 0 1 0 1 1 1 0x17
Current110 X 0 0 1 1 0 0 0 0x18
Current132 X 0 0 1 1 0 0 1 0x19
Current154 X 0 0 1 1 0 1 0 0x1A
Current176 X 0 0 1 1 0 1 1 0x1B
Current198 X 0 0 1 1 1 0 0 0x1C
Current1BA X 0 0 1 1 1 0 1 0x1D
Current1DC X 0 0 1 1 1 1 0 0x1E
Current1FE X 0 0 1 1 1 1 1 0x1F
Port 0 only (virtual port, no action) X 0 1 0 0 0 0 0 0x20
Port 1 only (virtual port, no action) X 0 1 0 0 0 0 1 0x21
Port 2 only (virtual port, no action) X 0 1 0 0 0 1 0 0x22
Port 3 only (virtual port, no action) X 0 1 0 0 0 1 1 0x23
Port 4 only (data bit D0; D7–D1 read as 0) X 0 1 0 0 1 0 0 0x24
Port 5 only (data bit D0; D7–D1 read as 0) X 0 1 0 0 1 0 1 0x25
Port 6 only (data bit D0; D7–D1 read as 0) X 0 1 0 0 1 1 0 0x26
Port 7 only (data bit D0; D7–D1 read as 0) X 0 1 0 0 1 1 1 0x27
Port 8 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 0 0 0 0x28
Port 9 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 0 0 1 0x29
Port 10 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 0 1 0 0x2A
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 13
COMMAND ADDRESS
REGISTER D15 D14 D13 D12 D11 D10 D9 D8
HEX
CODE
Port 11 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 0 1 1 0x2B
Port 12 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 1 0 0 0x2C
Port 13 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 1 0 1 0x2D
Port 14 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 1 1 0 0x2E
Port 15 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 1 1 1 0x2F
Port 16 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 0 0 0 0x30
Port 17 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 0 0 1 0x31
Port 18 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 0 1 0 0x32
Port 19 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 0 1 1 0x33
Port 20 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 1 0 0 0x34
Port 21 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 1 0 1 0x35
Port 22 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 1 1 0 0x36
Port 23 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 1 1 1 0x37
Port 24 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 0 0 0 0x38
Port 25 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 0 0 1 0x39
Port 26 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 0 1 0 0x3A
Port 27 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 0 1 1 0x3B
Port 28 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 1 0 0 0x3C
Port 29 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 1 0 1 0x3D
Port 30 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 1 1 0 0x3E
Port 31 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 1 1 1 0x3F
4 ports 4–7 (data bits D0–D3; D4–D7 read as 0) X 1 0 0 0 0 0 0 0x40
5 ports 4–8 (data bits D0–D4; D5–D7 read as 0) X 1 0 0 0 0 0 1 0x41
6 ports 4–9 (data bits D0–D5; D6–D7 read as 0) X 1 0 0 0 0 1 0 0x42
7 ports 4–10 (data bits D0–D6; D7 reads as 0) X 1 0 0 0 0 1 1 0x43
8 ports 4–11 (data bits D0–D7) X 1 0 0 0 1 0 0 0x44
8 ports 5–12 (data bits D0–D7) X 1 0 0 0 1 0 1 0x45
8 ports 6–13 (data bits D0–D7) X 1 0 0 0 1 1 0 0x46
8 ports 7–14 (data bits D0–D7) X 1 0 0 0 1 1 1 0x47
8 ports 8–15 (data bits D0–D7) X 1 0 0 1 0 0 0 0x48
8 ports 9–16 (data bits D0–D7) X 1 0 0 1 0 0 1 0x49
8 ports 10–17 (data bits D0–D7) X 1 0 0 1 0 1 0 0x4A
8 ports 11–18 (data bits D0–D7) X 1 0 0 1 0 1 1 0x4B
8 ports 12–19 (data bits D0–D7) X 1 0 0 1 1 0 0 0x4C
8 ports 13–20 (data bits D0–D7) X 1 0 0 1 1 0 1 0x4D
8 ports 14–21 (data bits D0–D7) X 1 0 0 1 1 1 0 0x4E
8 ports 15–22 (data bits D0–D7) X 1 0 0 1 1 1 1 0x4F
Table 5. Register Address Map (continued)
MAX6956
quently changes, the MAX6956’s address pointer, then
master 1’s delayed read may be from an unexpected
location.
Command Address Autoincrementing
Address autoincrementing allows the MAX6956 to be
configured with the shortest number of transmissions
by minimizing the number of times the command
address needs to be sent. The command address
stored in the MAX6956 generally increments after each
data byte is written or read (Table 4).
Initial Power-Up
On initial power-up, all control registers are reset, the
current registers are set to minimum value, and the
MAX6956 enters shutdown mode (Table 6).
LED Current Control
LED segment drive current can be set either globally or
individually. Global control simplifies the operation
when all LEDs are set to the same current level,
because writing just the global current register sets the
current for all ports configured as LED segment drivers.
It is also possible to individually control the current
drive of each LED segment driver. Individual/global
brightness control is selected by setting the configura-
tion register I bit (Table 9). The global current register
(0x02) data are then ignored, and segment currents are
set using register addresses 0x12 through 0x1F (Tables
12, 13, and 14). Each segment is controlled by a nibble
of one of the 16 current registers.
Transition (Port Data Change) Detection
Port transition detection allows any combination of the
seven ports P24–P30 to be continuously monitored for
changes in their logic status (Figure 11). A detected
change is flagged on the transition detection mask reg-
ister INT status bit, D7 (Table 15). If port P31 is config-
ured as an output (Tables 1 and 2), then P31 also
automatically becomes an active-high interrupt output
(INT), which follows the condition of the INT status bit.
Port P31 is set as output by writing bit D7 = 0 and bit
D6 = 1 to the port configuration register (Table 1). Note
that the MAX6956 does not identify which specific
port(s) caused the interrupt, but provides an alert that
one or more port levels have changed.
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
14 ______________________________________________________________________________________
COMMAND ADDRESS
REGISTER D15 D14 D13 D12 D11 D10 D9 D8
HEX
CODE
8 ports 16–23 (data bits D0–D7) X 1 0 1 0 0 0 0 0x50
8 ports 17–24 (data bits D0–D7) X 1 0 1 0 0 0 1 0x51
8 ports 18–25 (data bits D0–D7) X 1 0 1 0 0 1 0 0x52
8 ports 19–26 (data bits D0–D7) X 1 0 1 0 0 1 1 0x53
8 ports 20–27 (data bits D0–D7) X 1 0 1 0 1 0 0 0x54
8 ports 21–28 (data bits D0–D7) X 1 0 1 0 1 0 1 0x55
8 ports 22–29 (data bits D0–D7) X 1 0 1 0 1 1 0 0x56
8 ports 23–30 (data bits D0–D7) X 1 0 1 0 1 1 1 0x57
8 ports 24–31 (data bits D0–D7) X 1 0 1 1 0 0 0 0x58
7 ports 25–31 (data bits D0–D6; D7 reads as 0) X 1 0 1 1 0 0 1 0x59
6 ports 26–31 (data bits D0–D5; D6–D7 read as 0) X 1 0 1 1 0 1 0 0x5A
5 ports 27–31 (data bits D0–D4; D5–D7 read as 0) X 1 0 1 1 0 1 1 0x5B
4 ports 28–31 (data bits D0–D3; D4–D7 read as 0) X 1 0 1 1 1 0 0 0x5C
3 ports 29–31 (data bits D0–D2; D3–D7 read as 0) X 1 0 1 1 1 0 1 0x5D
2 ports 30–31 (data bits D0–D1; D2–D7 read as 0) X 1 0 1 1 1 1 0 0x5E
1 port 31 only (data bit D0; D1–D7 read as 0) X 1 0 1 1 1 1 1 0x5F
Table 5. Register Address Map (continued)
Note: Unused bits read as 0.
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
Table 6. Power-Up Configuration
REGISTER DATA
REGISTER
FUNCTION POWER-UP CONDITION
ADDRESS
CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Port Register
Bits 4 to 31 LED Off; GPIO Output Low 0x24 to
0x3F XXXXXXX0
Global
Current 1/16 (minimum on) 0x02 X X X X 0 0 0 0
Configuration
Register
Shutdown Enabled
Current Control = Global
Transition Detection Disabled
0x04 0 0 X X X X X 0
Input Mask
Register All Clear (Masked Off) 0x06 X 0 0 0 0 0 0 0
Display Test Normal Operation 0x07 X X X X X X X 0
Port
Configuration P7, P6, P5, P4: GPIO Inputs Without Pullup 0x09 1 0 1 0 1 0 1 0
Port
Configuration P11, P10, P9, P8: GPIO Inputs Without Pullup 0x0A 1 0 1 0 1 0 1 0
Port
Configuration P15, P14, P13, P12: GPIO Inputs Without Pullup 0x0B 1 0 1 0 1 0 1 0
Port
Configuration P19, P18, P17, P16: GPIO Inputs Without Pullup 0x0C 1 0 1 0 1 0 1 0
Port
Configuration P23, P22, P21, P20: GPIO Inputs Without Pullup 0x0D 1 0 1 0 1 0 1 0
Port
Configuration P27, P26, P25, P24: GPIO Inputs Without Pullup 0x0E 1 0 1 0 1 0 1 0
Port
Configuration P31, P30, P29, P28: GPIO Inputs Without Pullup 0x0F 1 0 1 0 1 0 1 0
Current054 1/16 (minimum on) 0x12 0 0 0 0 0 0 0 0
Current076 1/16 (minimum on) 0x13 0 0 0 0 0 0 0 0
Current098 1/16 (minimum on) 0x14 0 0 0 0 0 0 0 0
Current0BA 1/16 (minimum on) 0x15 0 0 0 0 0 0 0 0
Current0DC 1/16 (minimum on) 0x16 0 0 0 0 0 0 0 0
Current0FE 1/16 (minimum on) 0x17 0 0 0 0 0 0 0 0
Current110 1/16 (minimum on) 0x18 0 0 0 0 0 0 0 0
Current132 1/16 (minimum on) 0x19 0 0 0 0 0 0 0 0
Current154 1/16 (minimum on) 0x1A 0 0 0 0 0 0 0 0
Current176 1/16 (minimum on) 0x1B 0 0 0 0 0 0 0 0
Current198 1/16 (minimum on) 0x1C 0 0 0 0 0 0 0 0
Current1BA 1/16 (minimum on) 0x1D 0 0 0 0 0 0 0 0
Current1DC 1/16 (minimum on) 0x1E 0 0 0 0 0 0 0 0
Current1FE 1/16 (minimum on) 0x1F 0 0 0 0 0 0 0 0
X = unused bits; if read, zero results.
______________________________________________________________________________________ 15
MAX6956
The mask register contains 7 mask bits, which select
which of the seven ports P24–P30 are to be monitored
(Table 15). Set the appropriate mask bit to enable that
port for transition detect. Clear the mask bit if transitions
on that port are to be ignored. Transition detection
works regardless of whether the port being monitored is
set to input or output, but generally, it is not particularly
useful to enable transition detection for outputs.
To use transition detection, first set up the mask register
and configure port P31 as an output, as described
above. Then enable transition detection by setting the
M bit in the configuration register (Table 10). Whenever
the configuration register is written with the M bit set,
the MAX6956 updates an internal 7-bit snapshot regis-
ter, which holds the comparison copy of the logic states
of ports P24 through P30. The update action occurs
regardless of the previous state of the M bit, so that it is
not necessary to clear the M bit and then set it again to
update the snapshot register.
When the configuration register is written with the M bit
set, transition detection is enabled and remains
enabled until either the configuration register is written
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
16 ______________________________________________________________________________________
Table 7. Configuration Register Format
REGISTER DATA
FUNCTION ADDRESS CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Configuration Register 0x04 M I XXXXXS
Table 8. Shutdown Control (S Data Bit D0) Format
REGISTER DATA
FUNCTION ADDRESS CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Shutdown 0x04 M I XXXXX0
Normal Operation 0x04 M I XXXXX1
Table 10. Transition Detection Control (M-Data Bit D7) Format
REGISTER DATA
FUNCTION ADDRESS CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Disabled 0x04 0 I XXXXXS
Enabled 0x04 1 I XXXXXS
REGISTER DATA
FUNCTION ADDRESS
CODE (HEX)
D7 D6 D5 D4 D3 D2 D1 D0
Global
Constant-current limits for all digits are
controlled by one setting in the Global Current
register, 0x02
0x04 M 0 XXXXXS
Individual Segment
Constant-current limit for each digit is
individually controlled by the settings in the
Current054 through Current1FE registers
0x04 M 1 XXXXXS
Table 9. Global Current Control (I Data Bit D6) Format
with the M bit clear, or a transition is detected. The INT
status bit (transition detection mask register bit D7)
goes low. Port P31 (if enabled as INT output) also goes
low, if it was not already low.
Once transition detection is enabled, the MAX6956
continuously compares the snapshot register against
the changing states of P24 through P31. If a change on
any of the monitored ports is detected, even for a short
time (like a pulse), the INT status bit (transition detec-
tion mask register bit D7) is set. Port P31 (if enabled as
INT output) also goes high. The INT output and INT sta-
tus bit are not cleared if more changes occur or if the
data pattern returns to its original snapshot condition.
The only way to clear INT is to access (read or write)
the transition detection mask register (Table 15). So if
the transition detection mask register is read twice in
succession after a transition event, the first time reads
with bit D7 set (identifying the event), and the second
time reads with bit D7 clear.
Transition detection is a one-shot event. When INT has
been cleared after responding to a transition event,
transition detection is automatically disabled, even
though the M bit in the configuration register remains
set (unless cleared by the user). Reenable transition
detection by writing the configuration register with the
M bit set, to take a new snapshot of the seven ports
P24 to P30.
Display Test Register
Display test mode turns on all ports configured as LED
drivers by overriding, but not altering, all controls and
port registers, except the port configuration register
(Table 16). Only ports configured as LED drivers are
affected. Ports configured as GPIO push-pull outputs
do not change state. In display test mode, each port’s
current is temporarily set to 1/2 the maximum current
limit as controlled by RISET.
Selecting External Component R
ISET
to Set Maximum Segment Current
The MAX6956 uses an external resistor RISET to set the
maximum segment current. The recommended value,
39kΩ, sets the maximum current to 24mA, which makes
the segment current adjustable from 1.5mA to 24mA in
1.5mA steps.
To set a different segment current, use the formula:
RISET = 936kΩ/ ISEG
where ISEG is the desired maximum segment current.
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 17
Table 11. Global Segment Current Register Format
LED DRIVE
FRACTION
TYPICAL SEGMENT
CURRENT (mA)
ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
1/16 1.5 0x02 X X X X 0 0 0 0 0xX0
2/16 3 0x02 X X X X 0 0 0 1 0xX1
3/16 4.5 0x02 X X X X 0 0 1 0 0xX2
4/16 6 0x02 X X X X 0 0 1 1 0xX3
5/16 7.5 0x02 X X X X 0 1 0 0 0xX4
6/16 9 0x02 X X X X 0 1 0 1 0xX5
7/16 10.5 0x02 X X X X 0 1 1 0 0xX6
8/16 12 0x02 X X X X 0 1 1 1 0xX7
9/16 13.5 0x02 X X X X 1 0 0 0 0xX8
10/16 15 0x02 X X X X 1 0 0 1 0xX9
11/16 16.5 0x02 X X X X 1 0 1 0 0xXA
12/16 18 0x02 X X X X 1 0 1 1 0xXB
13/16 19.5 0x02 X X X X 1 1 0 0 0xXC
14/16 21 0x02 X X X X 1 1 0 1 0xXD
15/16 22.5 0x02 X X X X 1 1 1 0 0xXE
16/16 24 0x02 X X X X 1 1 1 1 0xXF
X = Don’t care bit.
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
18 ______________________________________________________________________________________
Table 12. Individual Segment Current Registers
REGISTER
FUNCTION
ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
Current054 register 0x12 Segment 5 Segment 4
Current076 register 0x13 Segment 7 Segment 6
Current098 register 0x14 Segment 9 Segment 8
Current0BA register 0x15 Segment 11 Segment 10
Current0DC register 0x16 Segment 13 Segment 12
Current0FE register 0x17 Segment 15 Segment 14
Current110 register 0x18 Segment 17 Segment 16
Current132 register 0x19 Segment 19 Segment 18
Current154 register 0x1A Segment 21 Segment 20
Current176 register 0x1B Segment 23 Segment 22
Current198 register 0x1C Segment 25 Segment 24
Current1BA register 0x1D Segment 27 Segment 26
Current1DC register 0x1E Segment 29 Segment 28
Current1FE register 0x1F Segment 31 Segment 30
Table 13. Even Individual Segment Current Format
LED DRIVE
FRACTION
SEGMENT
CONSTANT
CURRENT WITH
RISET = 39kΩ (mA)
ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
1/16 1.5 0x12 to 0x1F 0000 0xX0
2/16 3 0x12 to 0x1F 0001 0xX1
3/16 4.5 0x12 to 0x1F 0010 0xX2
4/16 6 0x12 to 0x1F 0011 0xX3
5/16 7.5 0x12 to 0x1F 0100 0xX4
6/16 9 0x12 to 0x1F 0101 0xX5
7/16 10.5 0x12 to 0x1F See Table 14. 0110 0xX6
8/16 12 0x12 to 0x1F 0111 0xX7
9/16 13.5 0x12 to 0x1F 1000 0xX8
10/16 15 0x12 to 0x1F 1001 0xX9
11/16 16.5 0x12 to 0x1F 1010 0xXA
12/16 18 0x12 to 0x1F 1011 0xXB
13/16 19.5 0x12 to 0x1F 1100 0xXC
14/16 21 0x12 to 0x1F 1101 0xXD
15/16 22.5 0x12 to 0x1F 1110 0xXE
16/16 24 0x12 to 0x1F 1111 0xXF
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 19
The recommended value of RISET is 39kΩ.
The recommended value of RISET is the minimum
allowed value, since it sets the display driver to the
maximum allowed segment current. RISET can be a
higher value to set the segment current to a lower maxi-
mum value where desired. The user must also ensure
that the maximum current specifications of the LEDs
connected to the driver are not exceeded.
The drive current for each segment can be controlled
through programming either the Global Current register
(Table 11) or Individual Segment Current registers
(Tables 12, 13, and 14), according to the setting of the
Current Control bit of the Configuration register (Table 9).
These registers select the LED’s constant-current drive
from 16 equal fractions of the maximum segment cur-
rent. The current difference between successive current
steps, ISTEP, is therefore determined by the formula:
ISTEP = ISEG / 16
If ISEG = 24mA, then ISTEP = 24mA / 16 = 1.5mA.
Applications Information
Driving Bicolor and Tricolor LEDs
Bicolor digits group a red and a green die together for
each display element, so that the element can be lit
red, green (or orange), depending on which die (or
both) is lit. The MAX6956 allows each segment’s cur-
rent to be set individually from 1/16th (minimum current
and LED intensity) to 16/16th (maximum current and
LED intensity), as well as off (zero current). Thus, a
bicolor (red-green) segment pair can be set to 289
color/intensity combinations. A discrete or CA tricolor
(red-green-yellow or red-green-blue) segment triad can
be set to 4913 color/intensity combinations.
Power Dissipation Issues
Each MAX6956 port can sink a current of 24mA into an
LED with a 2.4V forward-voltage drop when operated
from a supply voltage of at least 3.0V. The minimum
voltage drop across the internal LED drivers is there-
fore (3.0V - 2.4V) = 0.6V. The MAX6956 can sink 28 x
24mA = 672mA when all outputs are operating as LED
Table 14. Odd Individual Segment Current Format
LED
DRIVE
FRACTION
SEGMENT
CONSTANT
CURRENT WITH
RISET = 39kΩ (mA)
ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
1/16 1.5 0x12 to 0x1F 0 0 0 0 0x0X
2/16 3 0x12 to 0x1F 0 0 0 1 0x1X
3/16 4.5 0x12 to 0x1F 0 0 1 0 0x2X
4/16 6 0x12 to 0x1F 0 0 1 1 0x3X
5/16 7.5 0x12 to 0x1F 0 1 0 0 0x4X
6/16 9 0x12 to 0x1F 0 1 0 1 0x5X
7/16 10.5 0x12 to 0x1F 0 1 1 0 See Table 13. 0x6X
8/16 12 0x12 to 0x1F 0 1 1 1 0x7X
9/16 13.5 0x12 to 0x1F 1 0 0 0 0x8X
10/16 15 0x12 to 0x1F 1 0 0 1 0x9X
11/16 16.5 0x12 to 0x1F 1 0 1 0 0xAX
12/16 18 0x12 to 0x1F 1 0 1 1 0xBX
13/16 19.5 0x12 to 0x1F 1 1 0 0 0xCX
14/16 21 0x12 to 0x1F 1 1 0 1 0xDX
15/16 22.5 0x12 to 0x1F 1 1 1 0 0xEX
16/16 24 0x12 to 0x1F 1 1 1 1 0xFX
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
20 ______________________________________________________________________________________
GPIO INPUT
CONDITIONING
P31
P30
P29
P28
P27
P26
P25
P24
GPIO/PORT OUTPUT LATCH
GPIO INPUT
CONDITIONING
GPIO/PORT OUTPUT LATCH
GPIO INPUT
CONDITIONING
GPIO/PORT OUTPUT LATCH
GPIO INPUT
CONDITIONING
GPIO/PORT OUTPUT LATCH
GPIO INPUT
CONDITIONING
GPIO/PORT OUTPUT LATCH
GPIO INPUT
CONDITIONING
GPIO/PORT OUTPUT LATCH
GPIO INPUT
CONDITIONING
GPIO/PORT OUTPUT LATCH
D Q
D Q
D Q
D Q
D Q
D Q
D Q
CLOCK PULSE WHEN WRITING CONFIGURATION REGISTER WITH M BIT SET
OR
CONFIGURATION REGISTER M BIT = 1
R
S
GPIO IN
GPIO/PORT OUT
CLOCK PULSE AFTER EACH READ ACCESS TO MASK REGISTER
INT STATUS STORED AS MSB OF MASK REGISTER
MASK REGISTER BIT 6
MASK REGISTER BIT 5
MASK REGISTER BIT 4
MASK REGISTER BIT 3
MASK REGISTER BIT 2
MASK REGISTER BIT 1
MASK REGISTER LSB
GPIO IN
GPIO/PORT OUT
GPIO IN
GPIO/PORT OUT
GPIO IN
GPIO/PORT OUT
GPIO IN
GPIO/PORT OUT
GPIO IN
GPIO/PORT OUT
GPIO IN
GPIO/PORT OUT
GPIO IN
GPIO/PORT OUT
GPIO INPUT
CONDITIONING
GPIO/PORT
OUTPUT LATCH
INT
OUTPUT LATCH
Figure 11. Maskable GPIO Ports P24 Through P31
segment drivers at full current. On a 3.3V supply, a
MAX6956 dissipates (3.3V - 2.4V) 672mA = 0.6W
when driving 28 of these 2.4V forward-voltage drop
LEDs at full current. This dissipation is within the ratings
of the 36-pin SSOP package with an ambient tempera-
ture up to +98°C. If a higher supply voltage is used or
the LEDs used have a lower forward-voltage drop than
2.4V, the MAX6956 absorbs a higher voltage, and the
MAX6956’s power dissipation increases.
If the application requires high drive current and high
supply voltage, consider adding a series resistor to
each LED to drop excessive drive voltage off-chip. For
example, consider the requirement that the MAX6956
must drive LEDs with a 2.0V to 2.4V specified forward-
voltage drop, from an input supply range is 5V ±5%
with a maximum LED current of 20mA. Minimum input
supply voltage is 4.75V. Maximum LED series resistor
value is (4.75V - 2.4V - 0.6V)/0.020A = 87.5Ω. We
choose 82Ω±2%. Worst-case resistor dissipation is at
maximum toleranced resistance, i.e., (0.020A)2(82Ω
1.02) = 34mW. The maximum MAX6956 dissipation
per LED is at maximum input supply voltage, minimum
toleranced resistance, minimum toleranced LED for-
ward-voltage drop, i.e., 0.020 x (5.25V - 2.0V - (0.020A
82Ωx 0.98)) = 32.86mW. Worst-case MAX6956 dissi-
pation is 920mW driving all 28 LEDs at 20mA full cur-
rent at once, which meets the 941mW dissipation
ratings of the 36-pin SSOP package.
Low-Voltage Operation
The MAX6956 operates down to 2V supply voltage
(although the sourcing and sinking currents are not guar-
anteed), providing that the MAX6956 is powered up ini-
tially to at least 2.5V to trigger the device’s internal reset.
Serial Interface Latency
When a MAX6956 register is written through the I2C inter-
face, the register is updated on the rising edge of SCL
during the data byte’s acknowledge bit (Figure 5). The
delay from the rising edge of SCL to the internal register
being updated can range from 50ns to 350ns.
PC Board Layout Considerations
Ensure that all of the MAX6956 GND connections are
used. A ground plane is not necessary, but may be useful
to reduce supply impedance if the MAX6956 outputs are
to be heavily loaded. Keep the track length from the ISET
pin to the RISET resistor as short as possible, and take the
GND end of the resistor either to the ground plane or
directly to the GND pins.
Power-Supply Considerations
The MAX6956 operates with power-supply voltages of
2.5V to 5.5V. Bypass the power supply to GND with a
0.047µF capacitor as close to the device as possible.
Add a 1µF capacitor if the MAX6956 is far away from
the board’s input bulk decoupling capacitor.
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 21
Table 15. Transition Detection Mask Register
REGISTER DATA
FUNCTION
REGISTER
ADDRESS
(HEX)
READ/
WRITE D7 D6 D5 D4 D3 D2 D1 D0
Read INT Status*
Mask
Register 0x06
Write Unchanged
Port
30
mask
Port
29
mask
Port
28
mask
Port
27
mask
Port
26
mask
Port
25
mask
Port
24
mask
*
INT is automatically cleared after it is read.
Table 16. Display Test Register
REGISTER DATA
MODE ADDRESS CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Normal Operation 0x07 XXXXXXX0
Display Test Mode 0x07 XXXXXXX1
X = Don’t care bit
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
22 ______________________________________________________________________________________
P5
P4
P7
P8
P6
P10
P9
P12
P13
P11
P15
P14
P17
P18
P16
P20
P19
a2
a1
c
d1
b
e
d2
g1
g2
f
i
h
k
l
j
dp
m
ca
P22
P23
P21
36
2
1
3
4
33
35
34
29
27
31
24
25
22
21
23
V+
GND
ISET
GND
AD0
AD1
SCL
P30
P29
P31
P27
P28
P25
P24
P26
32
30
26
5
7
9
28
6
8
11
10
12
14
15
13
17
16
19
20
18
SDA
MAX6956AAX
U1
39kΩ
3V
3V
DATA
CLOCK
LED1
P5
P4
P7
P8
P6
P10
P9
P12
P13
P11
P15
P14
P17
P18
P16
P20
P19
a2
a1
c
d1
b
e
d2
g1
g2
f
i
h
k
l
j
dp
m
ca
P22
P23
P21
36
2
1
3
4
33
35
34
29
27
31
24
25
22
21
23
V+
GND
ISET
GND
AD0
AD1
SCL
P30
P29
P31
P27
P28
P25
P24
P26
32
30
26
5
7
9
28
6
8
11
10
12
14
15
13
17
16
19
20
18
SDA
MAX6956AAX
39kΩ
3V
IRQ OUT
LED3
a2
a1
c
d1
b
e
d2
g1
g2
f
i
h
k
l
j
dp
m
ca
LED2
212
SW3
SW2SW1
U2
47nF
47nF
Typical Operating Circuit
MAX6956
MAX6956
P4
P31
P30
P6
P28
P27
P26
P29
P7
P5
P9
P13
P10
P14
P11
P15
P16
P17
P12
P8 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
P21
P22
P23
P25
N.C.
P20
P19
P18
N.C.
GND
GND
GND
ISET
V+
AD1
SCL
SDA
N.C.
AD0
TQFN
P24
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 23
36
35
34
33
32
31
30
29
28
27
26
25
24
23
1
2
3
4
5
6
7
8
9
10
11
12
13
14
V+
AD1
SCL
SDA
P4
P31
P26
P5
P30
P6
P29
P7
P28
P27
P17
P16
P15
P11
P14
P10
P13
P9
P12
P8
AD0
GND
GND
ISET
SSOP
TOP VIEW
MAX6956
22
21
20
19
15
16
17
18 P22
P25
P24
P23
P21
P20
P19
P18
Pin Configurations (continued)
Chip Information
PROCESS: CMOS
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in
the package code indicates RoHS status only. Package draw-
ings may show a different suffix character, but the drawing per-
tains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
28 DIP N28+2 21-0043 —
28 SSOP A28+1 21-0056 90-0095
36 SSOP A36+4 21-0040 90-0098
40 Thin QFN-EP T4066+5 21-0141 90-0055
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
24
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
2 11/03 — —
3 3/09 Added exposed pad information and updated packaging information 1, 2, 5, 23
4 6/10 Added lead-free and automotive qualified parts to Ordering Information 1
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