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19-2414; Rev 3; 3/09
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander
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 sinking 10mA and sourcing 4.5mA, or a Schmitt logic input with optional internal pullup. Seven ports feature configurable 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 I 2C 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 capability, refer to the MAX7300 data sheet.
2
Features
o 400kbps I C-Compatible Serial Interface o 2.5V to 5.5V Operation o -40C to +125C Temperature Range o 20 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 o 11A (max) Shutdown Current o 16-Step Individually Programmable Current Control for Each LED o Logic Transition Detection for Seven I/O Ports
MAX6956
Ordering Information
PART MAX6956ANI MAX6956AAI MAX6956AAX TEMP RANGE -40C to +125C -40C to +125C -40C to +125C PIN-PACKAGE 28 DIP 28 SSOP 36 SSOP 40 Thin QFN-EP*
MAX6956ATL -40C to +125C *EP = Exposed pad.
Pin Configurations
TOP VIEW
ISET 1 GND 2 GND 3 AD0 4 P12 5 P13 6 P14 7 28 V+ 27 AD1 26 SCL 25 SDA 24 P31
Applications
Set-Top Boxes Panel Meters White Goods Automotive Bar Graph Displays Industrial Controllers System Monitoring
MAX6956
23 P30 22 P29 21 P28 20 P27 19 P26 18 P25 17 P24 16 P23 15 P22
Typical Operating Circuit appears at end of data sheet.
P15 8 P16 9 P17 10 P18 11 P19 12 P20 13 P21 14
SSOP/DIP
Pin Configurations continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
ABSOLUTE MAXIMUM RATINGS
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 = +70C) 1143mW 28-Pin SSOP (derate 9.1mW/C above TA = +70C) ...727mW 36-Pin SSOP (derate 11.8mW/C above TA = +70C) ...941mW 40-Pin TQFN (derate 26.3mW/C above TA = +70C) 2105mW Operating Temperature Range (TMIN to TMAX) ...............................................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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.
ELECTRICAL CHARACTERISTICS
(Typical Operating Circuit, V+ = 2.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER Operating Supply Voltage Shutdown Supply Current SYMBOL V+ ISHDN CONDITIONS TA = +25C TA = -40C to +85C TA = TMIN to TMAX All ports programmed as outputs high, no load, all other inputs at V+ or GND All ports programmed as outputs low, no load, all other inputs at V+ or GND TA = +25C TA = -40C to +85C TA = TMIN to TMAX TA = +25C TA = -40C to +85C TA = TMIN to TMAX 110 170 180 MIN 2.5 TYP 5.5 MAX 5.5 8 10 11 230 250 270 210 230 240 135 140 145 0.7 V+ 0.3 V+ GPIO inputs without pullup, VPORT = V+ to GND V+ = 2.5V V+ = 5.5V GPIO outputs, ISOURCE = 2mA, TA = -40C to +85C GPIO outputs, ISOURCE = 1mA, TA = TMIN to TMAX (Note 2) VPORT = 0.6V Port configured output low, shorted to V+ -100 12 80 V+ 0.7 V+ 0.7 2 2.75 10 11 18 20 1 19 120 0.3 +100 30 180 A A A A UNITS V
All digital inputs at V+ or GND
Operating Supply Current
IGPOH
Operating Supply Current
IGPOL
Operating Supply Current
ILED
All ports programmed TA = +25C as LED outputs, all LEDs TA = -40C to +85C off, no load, all other inputs at V+ or GND TA = TMIN to TMAX
INPUTS AND OUTPUTS Logic-High Input Voltage Port Inputs Logic-Low Input Voltage Port Inputs Input Leakage Current GPIO Input Internal Pullup to V+ Hysteresis Voltage GPIO Inputs VIH VIL IIH, IIL IPU VI V V nA A V
Output High Voltage
VOH
V
Port Sink Current Output Short-Circuit Current
IOL IOLSC
mA mA
2
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander
ELECTRICAL CHARACTERISTICS (continued)
(Typical Operating Circuit, V+ = 2.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS V+ = 2.5V, VLED = 2.3V at maximum LED current V+ = 3.3V, VLED = 2.4V at maximum LED IDIGIT current (Note 2) V+ = 5.5V, VLED = 2.4V at maximum LED current V+ = 2.5V, VOUT = 0.6V at maximum sink current IDIGIT_SC V+ = 5.5V, VOUT = 0.6V at maximum sink current VIH VIL IIH, IIL VOL (Note 2) ISINK = 6mA -50 MIN 9.5 18.5 19 18.5 19 0.7 V+ 0.3 V+ 50 10 0.4 TYP 13.5 24 25 23 24 MAX 18 27.5 30 28 mA 28 V V nA pF V mA UNITS
MAX6956
Port Drive LED Sink Current, Port Configured as LED Driver
Port Drive Logic Sink Current, Port Configured as LED Driver Input High-Voltage SDA, SCL, AD0, AD1 Input Low-Voltage SDA, SCL, AD0, AD1 Input Leakage Current SDA, SCL Input Capacitance Output Low-Voltage SDA
TIMING CHARACTERISTICS (Figure 2)
(V+ = 2.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER Serial Clock Frequency Bus Free Time Between a STOP and a START Condition Hold Time (Repeated) START Condition Repeated START Condition Setup Time STOP Condition Setup Time Data Hold Time Data Setup Time SCL Clock Low Period SCL Clock High Period Rise Time of Both SDA and SCL Signals, Receiving Fall Time of Both SDA and SCL Signals, Receiving Fall Time of SDA Transmitting SYMBOL fSCL tBUF tHD, STA tSU, STA tSU, STO tHD, DAT tSU, DAT tLOW tHIGH tR tF tF,TX (Note 3) CONDITIONS MIN 1.3 0.6 0.6 0.6 15 100 1.3 0.7 20 + 0.1Cb 20 + 0.1Cb 20 + 0.1Cb 900 TYP MAX 400 UNITS kHz s s s s ns ns s s ns ns ns
(Notes 2, 4) (Notes 2, 4) (Notes 2, 5)
300 300 250
Pulse Width of Spike Suppressed tSP (Notes 2, 6) 0 50 ns Capacitive Load for Each Bus (Note 2) 400 pF Cb Line Note 1: All parameters tested at TA = +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 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. tR and tF measured between 0.3V+ and 0.7V+. Note 5: ISINK 6mA. Cb = total capacitance of one bus line in pF. tR and tF measured between 0.3V+ and 0.7V+. Note 6: Input filters on the SDA and SCL inputs suppress noise spikes less than 50ns.
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
__________________________________________Typical Operating Characteristics
(RISET = 39k, TA = +25C, unless otherwise noted.)
OPERATING SUPPLY CURRENT vs. TEMPERATURE
MAX6956 toc01
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
MAX6956 toc02
OPERATING SUPPLY CURRENT vs. V+ (NO LOADS)
ALL PORTS LED (ON) SUPPLY CURRENT (mA) 10 ALL PORTS OUTPUT (1) 1 ALL PORTS OUTPUT (0)
MAX6956 toc03
0.40 0.36 0.32 SUPPLY CURRENT (mA) 0.28 0.24 0.20 0.16 0.12 0.08 0.04 0 -40.0 -12.5 15.0 42.5 70.0 97.5 ALL PORTS LED (OFF) ALL PORTS OUTPUT (1) ALL PORTS OUTPUT (0) V+ = 2.5V TO 5.5V NO LOAD
8 V+ = 5.5V 7 SUPPLY CURRENT (A) V+ = 3.3V 6
100
5
V+ = 2.5V
4
0.1 ALL PORTS LED (OFF)
3 125.0 -40.0 -12.5 15.0 42.5 70.0 97.5 125.0 TEMPERATURE (C) TEMPERATURE (C)
0.01 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 V+ (V)
LED DRIVER SINK CURRENT vs. V+
MAX6956 toc04
LED DRIVER SINK CURRENT vs. TEMPERATURE
VLED = 2.4V 26 PORT SINK CURRENT (mA) 25 24 23 V+ = 3.3V 22 21 20 V+ = 5.5V
MAX6956 toc05
GPO SINK CURRENT vs. TEMPERATURE (OUTPUT = 0)
V+ = 2.5V TO 5.5V, VPORT = 0.6V 16 PORT SINK CURRENT (mA) 14 12 10 8 6 4 2 -40.0 -12.5 15.0 42.5 70.0 97.5 125.0
MAX6956 toc06
26 24 PORT SINK CURRENT (mA) 22 20 18 16 14 12 10 8 6 2.0 2.5 3.0 3.5 4.0 4.5 5.0 LED DROP = 1.8V LED DROP = 2.4V
27
18
5.5
-40.0
-12.5
15.0
42.5
70.0
97.5
125.0
V+ (V)
TEMPERATURE (C)
TEMPERATURE (C)
GPO SOURCE CURRENT vs. TEMPERATURE (OUTPUT = 1)
MAX6956 toc07
GPI PULLUP CURRENT vs. TEMPERATURE
MAX6956 toc08
GPO SHORT-CIRCUIT CURRENT vs. TEMPERATURE
MAX6956 toc09
9 VPORT = 1.4V 8 PORT SOURCE CURRENT (mA) 7 6 5 4 3 2 -40.0 -12.5 15.0 42.5 70.0 97.5 V+ = 5.5V V+ = 3.3V V+ = 2.5V
1000
100
PULLUP CURRENT (A)
V+ = 5.5V
PORT CURRENT (mA)
GPO = 0, PORT SHORTED TO V+ 10
100 V+ = 3.3V
V+ = 2.5V 10 125.0 -40.0 -12.5 15.0 42.5 70.0 97.5 125.0 TEMPERATURE (C) TEMPERATURE (C) 1 -40.0
GPO = 1, PORT SHORTED TO GND -12.5 15.0 42.5 70.0 97.5 125.0
TEMPERATURE (C)
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander
Pin Description
PIN SSOP/DIP 1 2, 3 4 SSOP 1 2, 3 4 TQFN 36 37, 38, 39 40 NAME ISET GND AD0 FUNCTION Segment Current Setting. Connect ISET to GND through a resistor (RISET) to set the maximum segment current. Ground Address Input 0. Sets device slave address. Connect to either GND, V+, SCL, SDA to give four logic combinations. See Table 3. 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. No Connection I2C-Compatible Serial Data I/O I2C-Compatible Serial Clock Input Address Input 1. Sets device slave address. Connect to either GND, V+, SCL, SDA to give four logic combinations. See Table 3. Positive Supply Voltage. Bypass V+ to GND with minimum 0.047F capacitor. Exposed Pad (TQFN Only). Not internally connected. Connect EP to ground plane for maximum thermal performance.
MAX6956
5-24
--
-- 1-10, 12-19, 21-30 11, 20, 31 32 33 34 35 --
P12-P31
-- -- 25 26 27 28 --
5-32 -- 33 34 35 36 --
P4-P31 N.C. SDA SCL AD1 V+ EP
Detailed Description
The MAX6956 LED driver/GPIO peripheral provides up to 28 I/O ports, P4 to P31, controlled through an I2C-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 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 segment 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 maskable 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 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.
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
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
Table 1. Port Configuration Map
REGISTER Port Configuration for P7, P6, P5, P4 Port Configuration for P11, P10, P9, P8 Port Configuration for P15, P14, P13, P12 Port Configuration for P19, P18, P17, P16 Port Configuration for P23, P22, P21, P20 Port Configuration for P27, P26, P25, P24 Port Configuration for P31, P30, P29, P28 ADDRESS CODE (HEX) 0x09 0x0A 0x0B 0x0C 0x0D 0x0E 0x0F REGISTER DATA D7 P7 P11 P15 P19 P23 P27 P31 D6 D5 P6 P10 P14 P18 P22 P26 P30 D4 D3 P5 P9 P13 P17 P21 P25 P29 D2 D1 P4 P8 P12 P16 P20 P24 P28 D0
Table 2. Port Configuration Matrix
MODE FUNCTION PORT REGISTER (0x20-0x5F) Register bit = 0 Output LED Segment Driver Register bit = 1 Register bit = 0 Register bit = 1 Register bit = input logic level PIN BEHAVIOR ADDRESS CODE (HEX) PORT CONFIGURATION BIT PAIR UPPER High impedance Open-drain current sink, with sink current (up to 24mA) determined by the appropriate current register Active-low logic output Active-high logic output Schmitt logic input Schmitt logic input with pullup 0x09 to 0x0F 0 0 LOWER
Output Input Input
GPIO Output GPIO Input Without Pullup GPIO Input with Pullup
0x09 to 0x0F 0x09 to 0x0F 0x09 to 0x0F
0 1 1
1 0 1
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.
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 second 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 nonexistent, so the instructions to these bits are ignored). Using 8-bit control, a seven-segment digit with a decimal point can be updated in a single byte-write, a 146
segment digit with DP can be updated in two bytewrites, 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 current 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 programmed while in shutdown mode. For minimum supply current in shutdown mode, logic inputs should be at GND or V+ potential. Shutdown mode is exited by setting the S bit in the configuration register (Table 8).
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
INTENSITY TEST CONFIGURATION P4 TO P31 LED DRIVERS OR GPIO INTENSITY REGISTERS TEST REGISTER PORT REGISTERS MASK REGISTER LED DRIVERS AND GPIO PORT CHANGE DETECTOR CONFIGURATION REGISTERS DATA 8 SEGMENT OR GPIO DATA 8 R/W CE R/W
MAX6956
AD0 AD1
ADDRESS MATCHER
COMMAND REGISTER DECODE
7
8
8
DATA BYTE
COMMAND BYTE
D0
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12
D13
D14
D15
7 7-BIT DEVICE ADDRESS SDA SCL SLAVE ADDRESS BYTE R/W
TO/FROM DATA REGISTERS
TO COMMAND REGISTERS
DATA BYTE
COMMAND BYTE
Figure 1. MAX6956 Functional Diagram
Shutdown mode is temporarily overridden by the display test function.
Serial Interface
Serial Addressing
The MAX6956 operates as a slave that sends and receives data through an I2C-compatible 2-wire interface. The interface uses a serial data line (SDA) and a serial clock line (SCL) to achieve bidirectional communication between master(s) and slave(s). A master (typically 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 4.7k,
is required on SDA. The MAX6956 SCL line operates only as an input. A pullup resistor, typically 4.7k, is required on SCL if there are multiple masters on the 2wire 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/ W bit (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 transmission with a START (S) condition by transitioning SDA from high to low while SCL is high. When the master
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
SDA
tBUF tSU, DAT tLOW SCL tHD, DAT tSU, STA tHD, STA tSU, STO
tHIGH tHD, STA tR START CONDITION tF REPEATED START CONDITION STOP CONDITION START CONDITION
Figure 2. 2-Wire Serial Interface Timing Details
SDA
SCL
S START CONDITION
P STOP CONDITION
Figure 3. Standard Stop Conditions
SDA
SCL
DATA LINE STABLE; DATA VALID
CHANGE OF DATA ALLOWED
Figure 4. Bit Transfer
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).
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 stable 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
Bit Transfer
One data bit is transferred during each clock pulse. The data on SDA must remain stable while SCL is high (Figure 4).
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
START CONDITION SCL 1 2 8 9 CLOCK PULSE FOR ACKNOWLEDGMENT
SDA BY TRANSMITTER
S SDA BY RECEIVER
Figure 5. Acknowledge
SDA 1 MSB SCL 0 0 A3 A2 A1 A0 LSB R/W ACK
Figure 6. Slave Address
MAX6956 is the recipient. When the MAX6956 is transmitting 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/ W bit. 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.
byte of information is the command byte. The command 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 condition is detected, these bytes are generally stored in subsequent 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 autoincrements 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 perform9
Message Format for Writing the MAX6956
A write to the MAX6956 comprises the transmission of the MAX6956's slave address with the R/ W bit set to zero, followed by at least 1 byte of information. The first
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
7-SEGMENT DIGIT 1 7-SEGMENT DIGIT 2 7-SEGMENT DIGIT 3 7-SEGMENT DIGIT 4 V+
VIRTUAL SEGMENTS 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 5
7-SEGMENT DIGIT 6
7-SEGMENT DIGIT 7
V+
VIRTUAL SEGMENTS 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
COMMAND BYTE IS STORED ON RECEIPT OF STOP CONDITION ACKNOWLEDGE FROM MAX6956 S SLAVE ADDRESS COMMAND BYTE RECEIVED R/W 0 A D15 D14 D13 D12 D11 D10 D9 D8
COMMAND BYTE ACKNOWLEDGE FROM MAX6956
A
P
Figure 8. Command Byte Received
ACKNOWLEDGE FROM MAX6956 HOW COMMAND BYTE AND DATA BYTE MAP INTO MAX6956's REGISTER ACKNOWLEDGE FROM MAX6956 S SLAVE ADDRESS R/W 0 A D15 D14 D13 D12 D11 D10 D9 D8 D7 D6
ACKNOWLEDGE FROM MAX6956 D5 D4 D3 D2 D1 D0
COMMAND BYTE
A
DATA BYTE 1 BYTE
A
P
Figure 9. Command and Single Data Byte Received
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
ACKNOWLEDGE FROM MAX6956 HOW COMMAND BYTE AND DATA BYTE MAP INTO MAX6956's REGISTER ACKNOWLEDGE FROM MAX6956 S SLAVE ADDRESS R/W 0 A COMMAND BYTE A DATA BYTE n BYTES AUTOINCREMENT MEMORY WORD ADDRESS A P D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 ACKNOWLEDGE FROM MAX6956 D5 D4 D3 D2 D1 D0
Figure 10. n Data Bytes Received
Table 3. MAX6956 Address Map
PIN CONNECTION AD1 GND GND GND GND V+ V+ V+ V+ SDA SDA SDA SDA SCL SCL SCL SCL AD0 GND V+ SDA SCL GND V+ SDA SCL GND V+ SDA SCL GND V+ SDA SCL A6 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 A5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 A4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 DEVICE ADDRESS A3 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 A2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 A1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 A0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
Table 4. Autoincrement Rules
COMMAND BYTE ADDRESS RANGE x0000000 to x1111110 x1111111 AUTOINCREMENT BEHAVIOR Command address autoincrements after byte read or written Command address remains at x1111111 after byte written or read
ing a write (Figure 8). The master can now read n consecutive bytes from the MAX6956, with the first data byte being read from the register addressed by the initialized command byte. When performing read-afterwrite 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 subse11
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
Table 5. Register Address Map
REGISTER No-Op Global Current Configuration Transition Detect Mask Display Test Port Configuration P7, P6, P5, P4 Port Configuration P11, P10, P9, P8 Port Configuration P15, P14, P13, P12 Port Configuration P19, P18, P17, P16 Port Configuration P23, P22, P21, P20 Port Configuration P27, P26, P25, P24 Port Configuration P31, P30, P29, P28 Current054 Current076 Current098 Current0BA Current0DC Current0FE Current110 Current132 Current154 Current176 Current198 Current1BA Current1DC Current1FE Port 0 only (virtual port, no action) Port 1 only (virtual port, no action) Port 2 only (virtual port, no action) Port 3 only (virtual port, no action) Port 4 only (data bit D0; D7-D1 read as 0) Port 5 only (data bit D0; D7-D1 read as 0) Port 6 only (data bit D0; D7-D1 read as 0) Port 7 only (data bit D0; D7-D1 read as 0) Port 8 only (data bit D0; D7-D1 read as 0) Port 9 only (data bit D0; D7-D1 read as 0) Port 10 only (data bit D0; D7-D1 read as 0) COMMAND ADDRESS D15 X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X D14 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D13 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 D12 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 D11 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 D10 0 0 1 1 1 0 0 0 1 1 1 1 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 D9 0 1 0 1 1 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 D8 0 0 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 HEX CODE 0x00 0x02 0x04 0x06 0x07 0x09 0x0A 0x0B 0x0C 0x0D 0x0E 0x0F 0x12 0x13 0x14 0x15 0x16 0x17 0x18 0x19 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F 0x20 0x21 0x22 0x23 0x24 0x25 0x26 0x27 0x28 0x29 0x2A
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
Table 5. Register Address Map (continued)
REGISTER Port 11 only (data bit D0; D7-D1 read as 0) Port 12 only (data bit D0; D7-D1 read as 0) Port 13 only (data bit D0; D7-D1 read as 0) Port 14 only (data bit D0; D7-D1 read as 0) Port 15 only (data bit D0; D7-D1 read as 0) Port 16 only (data bit D0; D7-D1 read as 0) Port 17 only (data bit D0; D7-D1 read as 0) Port 18 only (data bit D0; D7-D1 read as 0) Port 19 only (data bit D0; D7-D1 read as 0) Port 20 only (data bit D0; D7-D1 read as 0) Port 21 only (data bit D0; D7-D1 read as 0) Port 22 only (data bit D0; D7-D1 read as 0) Port 23 only (data bit D0; D7-D1 read as 0) Port 24 only (data bit D0; D7-D1 read as 0) Port 25 only (data bit D0; D7-D1 read as 0) Port 26 only (data bit D0; D7-D1 read as 0) Port 27 only (data bit D0; D7-D1 read as 0) Port 28 only (data bit D0; D7-D1 read as 0) Port 29 only (data bit D0; D7-D1 read as 0) Port 30 only (data bit D0; D7-D1 read as 0) Port 31 only (data bit D0; D7-D1 read as 0) 4 ports 4-7 (data bits D0-D3; D4-D7 read as 0) 5 ports 4-8 (data bits D0-D4; D5-D7 read as 0) 6 ports 4-9 (data bits D0-D5; D6-D7 read as 0) 7 ports 4-10 (data bits D0-D6; D7 reads as 0) 8 ports 4-11 (data bits D0-D7) 8 ports 5-12 (data bits D0-D7) 8 ports 6-13 (data bits D0-D7) 8 ports 7-14 (data bits D0-D7) 8 ports 8-15 (data bits D0-D7) 8 ports 9-16 (data bits D0-D7) 8 ports 10-17 (data bits D0-D7) 8 ports 11-18 (data bits D0-D7) 8 ports 12-19 (data bits D0-D7) 8 ports 13-20 (data bits D0-D7) 8 ports 14-21 (data bits D0-D7) 8 ports 15-22 (data bits D0-D7) COMMAND ADDRESS D15 X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X D14 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 D13 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D12 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D11 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 D10 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 D9 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 D8 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 HEX CODE 0x2B 0x2C 0x2D 0x2E 0x2F 0x30 0x31 0x32 0x33 0x34 0x35 0x36 0x37 0x38 0x39 0x3A 0x3B 0x3C 0x3D 0x3E 0x3F 0x40 0x41 0x42 0x43 0x44 0x45 0x46 0x47 0x48 0x49 0x4A 0x4B 0x4C 0x4D 0x4E 0x4F
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
Table 5. Register Address Map (continued)
REGISTER 8 ports 16-23 (data bits D0-D7) 8 ports 17-24 (data bits D0-D7) 8 ports 18-25 (data bits D0-D7) 8 ports 19-26 (data bits D0-D7) 8 ports 20-27 (data bits D0-D7) 8 ports 21-28 (data bits D0-D7) 8 ports 22-29 (data bits D0-D7) 8 ports 23-30 (data bits D0-D7) 8 ports 24-31 (data bits D0-D7) 7 ports 25-31 (data bits D0-D6; D7 reads as 0) 6 ports 26-31 (data bits D0-D5; D6-D7 read as 0) 5 ports 27-31 (data bits D0-D4; D5-D7 read as 0) 4 ports 28-31 (data bits D0-D3; D4-D7 read as 0) 3 ports 29-31 (data bits D0-D2; D3-D7 read as 0) 2 ports 30-31 (data bits D0-D1; D2-D7 read as 0) 1 port 31 only (data bit D0; D1-D7 read as 0) COMMAND ADDRESS D15 X X X X X X X X X X X X X X X X D14 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 D13 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D12 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 D11 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 D10 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 D9 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 D8 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 HEX CODE 0x50 0x51 0x52 0x53 0x54 0x55 0x56 0x57 0x58 0x59 0x5A 0x5B 0x5C 0x5D 0x5E 0x5F
Note: Unused bits read as 0.
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).
drive of each LED segment driver. Individual/global brightness control is selected by setting the configuration 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.
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
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 register INT status bit, D7 (Table 15). If port P31 is configured 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.
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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 FUNCTION Port Register Bits 4 to 31 Global Current Configuration Register Input Mask Register Display Test Port Configuration Port Configuration Port Configuration Port Configuration Port Configuration Port Configuration Port Configuration Current054 Current076 Current098 Current0BA Current0DC Current0FE Current110 Current132 Current154 Current176 Current198 Current1BA Current1DC Current1FE POWER-UP CONDITION ADDRESS CODE (HEX) 0x24 to 0x3F 0x02 REGISTER DATA D7 X X D6 X X D5 X X D4 X X D3 X 0 D2 X 0 D1 X 0 D0 0 0
MAX6956
LED Off; GPIO Output Low 1/16 (minimum on) Shutdown Enabled Current Control = Global Transition Detection Disabled All Clear (Masked Off) Normal Operation P7, P6, P5, P4: GPIO Inputs Without Pullup P11, P10, P9, P8: GPIO Inputs Without Pullup P15, P14, P13, P12: GPIO Inputs Without Pullup P19, P18, P17, P16: GPIO Inputs Without Pullup P23, P22, P21, P20: GPIO Inputs Without Pullup P27, P26, P25, P24: GPIO Inputs Without Pullup P31, P30, P29, P28: GPIO Inputs Without Pullup 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on) 1/16 (minimum on)
0x04
0
0
X
X
X
X
X
0
0x06 0x07 0x09 0x0A 0x0B 0x0C 0x0D 0x0E 0x0F 0x12 0x13 0x14 0x15 0x16 0x17 0x18 0x19 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F
X X 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 X 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 X 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 X 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 X 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 X 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 X 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
X = unused bits; if read, zero results.
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
Table 7. Configuration Register Format
FUNCTION Configuration Register ADDRESS CODE (HEX) 0x04 REGISTER DATA D7 M D6 I D5 X D4 X D3 X D2 X D1 X D0 S
Table 8. Shutdown Control (S Data Bit D0) Format
FUNCTION Shutdown Normal Operation ADDRESS CODE (HEX) 0x04 0x04 REGISTER DATA D7 M M D6 I I D5 X X D4 X X D3 X X D2 X X D1 X X D0 0 1
Table 9. Global Current Control (I Data Bit D6) Format
FUNCTION ADDRESS CODE (HEX) D7 Global Constant-current limits for all digits are controlled by one setting in the Global Current register, 0x02 Individual Segment Constant-current limit for each digit is individually controlled by the settings in the Current054 through Current1FE registers D6 D5 REGISTER DATA D4 D3 D2 D1 D0
0x04
M
0
X
X
X
X
X
S
0x04
M
1
X
X
X
X
X
S
Table 10. Transition Detection Control (M-Data Bit D7) Format
FUNCTION Disabled Enabled ADDRESS CODE (HEX) 0x04 0x04 REGISTER DATA D7 0 1 D6 I I D5 X X D4 X X D3 X X D2 X X D1 X X D0 S S
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
16
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 register, 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
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
Table 11. Global Segment Current Register Format
LED DRIVE FRACTION 1/16 2/16 3/16 4/16 5/16 6/16 7/16 8/16 9/16 10/16 11/16 12/16 13/16 14/16 15/16 16/16 TYPICAL SEGMENT CURRENT (mA) 1.5 3 4.5 6 7.5 9 10.5 12 13.5 15 16.5 18 19.5 21 22.5 24 ADDRESS CODE (HEX) 0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x02 D7 X X X X X X X X X X X X X X X X D6 X X X X X X X X X X X X X X X X D5 X X X X X X X X X X X X X X X X D4 X X X X X X X X X X X X X X X X D3 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 D2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 D1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 D0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 HEX CODE 0xX0 0xX1 0xX2 0xX3 0xX4 0xX5 0xX6 0xX7 0xX8 0xX9 0xXA 0xXB 0xXC 0xXD 0xXE 0xXF
X = Don't care bit.
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 detection mask register bit D7) is set. Port P31 (if enabled as INT output) also goes high. The INT output and INT status 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 RISET to Set Maximum Segment Current The MAX6956 uses an external resistor RISET to set the maximum segment current. The recommended value, 39k, 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 = 936k / ISEG where ISEG is the desired maximum segment current.
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
Table 12. Individual Segment Current Registers
REGISTER FUNCTION Current054 register Current076 register Current098 register Current0BA register Current0DC register Current0FE register Current110 register Current132 register Current154 register Current176 register Current198 register Current1BA register Current1DC register Current1FE register ADDRESS CODE (HEX) 0x12 0x13 0x14 0x15 0x16 0x17 0x18 0x19 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F D7 D6 D5 D4 D3 D2 D1 D0
Segment 5 Segment 7 Segment 9 Segment 11 Segment 13 Segment 15 Segment 17 Segment 19 Segment 21 Segment 23 Segment 25 Segment 27 Segment 29 Segment 31
Segment 4 Segment 6 Segment 8 Segment 10 Segment 12 Segment 14 Segment 16 Segment 18 Segment 20 Segment 22 Segment 24 Segment 26 Segment 28 Segment 30
Table 13. Even Individual Segment Current Format
LED DRIVE FRACTION SEGMENT CONSTANT CURRENT WITH RISET = 39k (mA) 1.5 3 4.5 6 7.5 9 10.5 12 13.5 15 16.5 18 19.5 21 22.5 24 ADDRESS CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
1/16 2/16 3/16 4/16 5/16 6/16 7/16 8/16 9/16 10/16 11/16 12/16 13/16 14/16 15/16 16/16
0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F See Table 14.
0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1
0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1
0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
0xX0 0xX1 0xX2 0xX3 0xX4 0xX5 0xX6 0xX7 0xX8 0xX9 0xXA 0xXB 0xXC 0xXD 0xXE 0xXF
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
Table 14. Odd Individual Segment Current Format
LED DRIVE FRACTION 1/16 2/16 3/16 4/16 5/16 6/16 7/16 8/16 9/16 10/16 11/16 12/16 13/16 14/16 15/16 16/16 SEGMENT CONSTANT CURRENT WITH RISET = 39k (mA) 1.5 3 4.5 6 7.5 9 10.5 12 13.5 15 16.5 18 19.5 21 22.5 24 ADDRESS CODE (HEX) 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F 0x12 to 0x1F D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1
0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1
0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 See Table 13.
0x0X 0x1X 0x2X 0x3X 0x4X 0x5X 0x6X 0x7X 0x8X 0x9X 0xAX 0xBX 0xCX 0xDX 0xEX 0xFX
The recommended value of RISET is 39k. The recommended value of R ISET 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 maximum 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 current. 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 current 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 therefore (3.0V - 2.4V) = 0.6V. The MAX6956 can sink 28 x 24mA = 672mA when all outputs are operating as LED
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
GPIO INPUT CONDITIONING GPIO/PORT OUTPUT LATCH
GPIO IN
GPIO/PORT OUT INT STATUS STORED AS MSB OF MASK REGISTER
P31 INT OUTPUT LATCH R S CLOCK PULSE AFTER EACH READ ACCESS TO MASK REGISTER
CONFIGURATION REGISTER M BIT = 1 GPIO INPUT CONDITIONING P30 GPIO/PORT OUTPUT LATCH GPIO INPUT CONDITIONING P29 GPIO/PORT OUTPUT LATCH GPIO INPUT CONDITIONING P28 GPIO/PORT OUTPUT LATCH GPIO IN GPIO IN D GPIO/PORT OUT Q MASK REGISTER BIT 4 GPIO IN GPIO IN D GPIO/PORT OUT Q MASK REGISTER BIT 6
D
Q MASK REGISTER BIT 5
GPIO/PORT OUT
GPIO INPUT CONDITIONING P27 GPIO/PORT OUTPUT LATCH GPIO INPUT CONDITIONING P26 GPIO/PORT OUTPUT LATCH GPIO INPUT CONDITIONING P25 GPIO/PORT OUTPUT LATCH
D
Q MASK REGISTER BIT 3
OR
GPIO/PORT OUT
GPIO IN D GPIO/PORT OUT Q MASK REGISTER BIT 2
GPIO IN
D
Q MASK REGISTER BIT 1
GPIO/PORT OUT
GPIO INPUT CONDITIONING P24 GPIO/PORT OUTPUT LATCH
GPIO IN D GPIO/PORT OUT Q MASK REGISTER LSB CLOCK PULSE WHEN WRITING CONFIGURATION REGISTER WITH M BIT SET
Figure 11. Maskable GPIO Ports P24 Through P31
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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
Table 15. Transition Detection Mask Register
FUNCTION REGISTER ADDRESS (HEX) READ/ WRITE Read 0x06 Write Unchanged REGISTER DATA D7 INT Status* D6 Port 30 mask D5 Port 29 mask D4 Port 28 mask D3 Port 27 mask D2 Port 26 mask D1 Port 25 mask D0 Port 24 mask
Mask Register
*INT is automatically cleared after it is read.
Table 16. Display Test Register
MODE Normal Operation Display Test Mode ADDRESS CODE (HEX) 0x07 0x07 REGISTER DATA D7 X X D6 X X D5 X X D4 X X D3 X X D2 X X D1 X X D0 0 1
X = Don't care bit
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 temperature up to +98C. 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 forwardvoltage 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 = 87.5. We choose 82 2%. Worst-case resistor dissipation is at maximum toleranced resistance, i.e., (0.020A)2 (82 1.02) = 34mW. The maximum MAX6956 dissipation per LED is at maximum input supply voltage, minimum toleranced resistance, minimum toleranced LED forward-voltage drop, i.e., 0.020 x (5.25V - 2.0V - (0.020A 82 x 0.98)) = 32.86mW. Worst-case MAX6956 dissipation is 920mW driving all 28 LEDs at 20mA full current 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 guaranteed), providing that the MAX6956 is powered up initially to at least 2.5V to trigger the device's internal reset.
Serial Interface Latency
When a MAX6956 register is written through the I2C interface, 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 0.047F capacitor as close to the device as possible. Add a 1F capacitor if the MAX6956 is far away from the board's input bulk decoupling capacitor.
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21
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
Typical Operating Circuit
3V 3V 36 47nF V+
U1
3 GND 2 GND 1 ISET 39k 35 AD1 4 AD0 33 SDA 34 SCL 31 P31 29 P30 27 P29 25 P28 24 P27 23 P26 22 P25 21 P24
MAX6956AAX
DATA CLOCK
32 P4 30 P5 28 P6 26 P7 5 P8 7 P9 P10 9 11 P11 6 P12 8 P13 10 P14 P15 12 13 P16 14 P17 15 P18 16 P19 P20 17 18 P21 P22 19 20 P23
a1 a2 b c d1 d2 e f g1 g2 h i j k l m dp ca
LED1
a1 a2 b c d1 d2 e f g1 g2 h i 3V 36 47nF 3 GND 2 GND 1 ISET 39k 35 AD1 4 AD0 33 SDA 34 SCL IRQ OUT P31 29 P30 27 P29 25 P28 24 P27 23 P26 22 P25 21 P24 31 V+ 32 P4 30 P5 28 P6 26 P7 5 P8 7 P9 P10 9 11 P11 6 P12 P13 8 10 P14 P15 12 13 P16 14 P17 15 P18 P19 16 P20 17 18 P21 P22 19 20 P23 j k l m dp ca
LED2
U2
MAX6956AAX
a1 a2 b c d1 d2 e f g1 g2 h i j k l m dp ca
LED3
1
2
SW1
SW2
SW3
22
______________________________________________________________________________________
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander
Pin Configurations (continued)
TOP VIEW
ISET 1 GND GND AD0 P8 P12 P9 P13 P10 2 3 4 5 6 7 8 9 36 V+ 35 AD1
MAX6956
GND GND
GND ISET V+ AD1 SCL SDA
37 36 35 34 33 32
34 SCL 33 SDA 32 P4
40
39
38
MAX6956
31
N.C.
AD0
31 P31 30 P5 29 P30 28 P6 27 P29 26 P7 25 P28 24 P27 23 P26 22 P25 21 P24 20 P23 19 P22
P8 P12 P9 P13 P10 P14 P11 P15 P16 P17
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
30 29 28 27 26
P4 P31 P5 P30 P6 P29 P7 P28 P27 P26
P14 10 P11 11 P15 12 P16 13 P17 14 P18 15 P19 16 P20 17 P21 18
MAX6956
25 24 23 22 21
N.C.
TQFN
SSOP
Chip Information
PROCESS: CMOS
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE 28 DIP 28 SSOP 36 SSOP 40 Thin QFN-EP PACKAGE CODE N28-2 A28-1 A36-4 T4066-5 DOCUMENT NO. 21-0043 21-0056 21-0040 21-0141
______________________________________________________________________________________
P25 N.C.
P18 P19 P20 P21 P22 P23
P24
23
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port LED Display Driver and I/O Expander MAX6956
Revision History
REVISION NUMBER 2 3 REVISION DATE 11/03 3/09 -- Added exposed pad information and updated packaging information DESCRIPTION PAGES CHANGED -- 1, 2, 5, 23
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 (c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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