Typical operating Circuit appears at end of data sheet.
QSPI is a trademark of Motorola, Inc.
MICROWIRE is a registered trademark of National
Semiconductor Corp.
General Description
The MAX6957 compact, serial-interfaced LED display
driver general-purpose I/O (GPIO) peripheral provides
microprocessors with up to 28 ports. Each port is indi-
vidually user configurable to either a logic input, logic
output, or common-anode (CA) LED constant-current
segment driver. Each port configured as an LED seg-
ment 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 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 MAX6957 is controlled
through an SPI-compatible 4-wire serial interface.
The MAX6957AAX and MAX6957ATL have 28 ports and
are available in 36-pin SSOP and 40-pin TQFN (6mm x
6mm) packages, respectively. The MAX6957AAI and
MAX6957ANI have 20 ports and are available in 28-pin
SSOP and 28-pin DIP packages, respectively.
For a 2-wire interfaced version, refer to the MAX6956
data sheet.
For a lower cost pin-compatible port expander without
the constant-current LED drive capability, refer to the
MAX7301 data sheet.
Applications
●Set-Top Boxes
●Panel Meters
●White Goods
●Bar Graph Displays
●Industrial Controllers
●System Monitoring
Features
● High-Speed 26MHz SPI-/QSPI™-/MICROWIRE®-
Compatible Serial Interface
●2.5V to 5.5V Operation
●-40°C to +125°C Temperature Range
●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
●11µA (max) Shutdown Current
●16-Step Individually Programmable Current Control
for Each LED
●Logic Transition Detection for Seven I/O Ports
Pin Configurations continued at end of data sheet.
*Exposed pad.
PART TEMP RANGE PIN-
PACKAGE
MAX6957ANI -40°C to +125°C 28 DIP
MAX6957AAI -40°C to +125°C 28 SSOP
MAX6957AAX -40°C to +125°C 36 SSOP
MAX6957ATL -40°C to +125°C 40 TQFN-EP*
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+
CS
SCLK
DIN
P31
P30
P22
P29
P28
P27
P26
P25
P24
P23
P21
P20
P19
P18
P17
P16
P15
P14
P13
P12
DOUT
GND
GND
ISET
SSOP/DIP
TOP VIEW
MAX6957
MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
19-2429; Rev 5; 7/14
Pin Congurations
Ordering Information
Voltage (with Respect to GND)
V+ ............................................................................-0.3V to +6V
All Other pins ...............................................-0.3V to (V+ + 0.3V)
P4–P31 Current ...............................................................±30mA
GND Current ....................................................................800mA
Continuous Power Dissipation (TA = +70°C)
28-Pin PDIP (derate 14.3mW/°C above +70°C) .......1143mW
28-Pin SSOP (derate 9.1mW/°C above +70°C) ..........727mW
36-Pin SSOP (derate 11.8mW/°C above +70°C) ........941mW
40-Pin TQFN (derate 37.0mW/°C above +70°C) ......2963mW
Operating Temperature Range (TMIN, TMAX) .... -40°C to +125°C
Junction Temperature ...................................................... +150°C
Storage Temperature Range ............................ -65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
(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
Shutdown Supply Current ISHDN
All digital inputs at
V+ or GND
TA = +25°C 5.5 8
µATA = -40°C to +85°C 10
TA = TMIN to TMAX 11
Operating Supply Current IGPOH
All ports programmed
As outputs high, no load,
All other inputs at V+ or
GND
TA = +25°C 180 230
µATA = -40°C to +85°C 250
TA = TMIN to TMAX 270
Operating Supply Current IGPOL
All ports programmed
As outputs low, no load,
All other inputs at V+ or
GND
TA = +25°C 170 210
µATA = -40°C to +85°C 230
TA = TMIN to TMAX 240
Operating Supply Current ILED
All ports programmed
as LED outputs, all LEDs
off, no load, all other
inputs at V+ or GND
TA = +25°C 110 135
µATA = -40°C to +85°C 140
TA = TMIN to TMAX 145
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
GPIO Input Internal Pullup to V+ IPU
V+ = 2.5V 12 19 30 µA
V+ = 5.5V 80 120 180
Hysteresis Voltage GPIO Inputs DVI0.3 V
Output High Voltage VOH
GPIO outputs, ISOURCE = 2mA, TA = -40°C to
+85°C
V+ -
0.7 V
GPIO outputs, ISOURCE = 1mA,
TA = TMIN to TMAX (Note 2)
V+ -
0.7 V
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Electrical Characteristics
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.
Absolute Maximum Ratings
Note 1: All parameters tested at TA = +25°C. Specifications over temperature are guaranteed by design.
Note 2: Guaranteed by design.
3(V+ = 2.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
(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
CLK Clock Period tCP 38.4 ns
CLK Pulse Width High tCH 19 ns
CLK Pulse Width Low tCL 19 ns
CS Fall to SCLK Rise Setup Time tCSS 9.5 ns
CLK Rise to CS Rise Hold Time tCSH 0 ns
DIN Setup Time tDS 9.5 ns
DIN Hold Time tDH 0 ns
Output Data Propagation Delay tDO CLOAD = 25pF 21 ns
Minimum CS Pulse High tCSW 19 ns
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Port Sink Current IOL VPORT = 0.6V 2 10 18 mA
Output Short-Circuit Current IOLSC Port congured output low, shorted to V+ 2.75 11 20 mA
Port Drive LED Sink Current,
Port Congured as LED Driver IPORT
V+ = 2.5V, VLED = 2.3V at maximum LED
current 9.5 13.5 18
mA
V+ = 3.3V, VLED = 2.4V at maximum LED
current (Note 2) 18.5 24 27.5
V+ = 5.5V, VLED = 2.4V at maximum LED
current 19 25 30
Port Drive Logic Sink Current,
Port Congured as LED Driver IPORT_SC
V+ = 2.5V, VOUT = 0.6V at maximum LED
current 18.5 23 28.0
mA
V+ = 5.5V, VOUT = 0.6V at maximum LED
current 19 24 28
Port LED Sink Current Matching ∆IPORT 6 %
Input High-Voltage SCLK, DIN,
CS VIH
V+ ≤ 3.3V 1.6 V
V+ > 3.3V 2
Input Low-Voltage SCLK, DIN, CS VIL 0.6 V
Input Leakage Current SCLK,
DIN, CS IIH, IIL -50 +50 nA
Output High-Voltage DOUT VOH ISOURCE = 1.6mA V+ -
0.5 V
Output Low-Voltage DOUT VOL ISINK = 1.6mA 0.4 V
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Timing Characteristics (Figure 3)
Electrical Characteristics (continued)
(RISET = 39kΩ, TA = +25°C, unless otherwise noted.)
GPO SHORT-CIRCUIT CURRENT
vs. TEMPERATURE
MAX6957 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
GPI PULLUP CURRENT
vs. TEMPERATURE
MAX6957 toc08
TEMPERATURE (°C)
PULLUP CURRENT (A)
97.570.042.515.0-12.5
100
1000
10
-40.0 125.0
V+ = 5.5V
V+ = 3.3V
V+ = 2.5V
GPO SOURCE CURRENT vs. TEMPERATURE
(OUTPUT = 1)
MAX6957 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
GPO SINK CURRENT vs. TEMPERATURE
(OUTPUT = 0)
MAX6957 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
LED DRIVER SINK CURRENT
vs. TEMPERATURE
MAX6957 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
LED DRIVER SINK CURRENT vs. V+
MAX6957 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
OPERATING SUPPLY CURRENT vs. V+
(NO LOADS)
MAX6957 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)
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX6957 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (A)
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. TEMPERATURE
MAX6957 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)
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Typical Operating Characteristics
Detailed Description
The MAX6957 LED driver/GPIO peripheral provides up
to 28 I/O ports, P4 to P31, controlled through an SPI-
compatible serial interface. The ports can be configured
to any combination of constant-current LED drivers, logic
inputs and logic outputs, and default to logic inputs on
power-up. When fully configured as an LED driver, the
MAX6957 controls up to 28 LED segments with individual
16-step adjustment of the constant current through each
LED segment. A single resistor sets the maximum seg-
ment current for all segments, with a maximum of 24mA
per segment. The MAX6957 drives any combination of
discrete LEDs and CA digits, including seven-segment
and starburst alphanumeric types.
Figure 1 is the MAX6957 functional diagram. Any I/O
port can be configured as a push-pull output (sink-
ing 10mA, sourcing 4.5mA), or a Schmitt-trigger logic
input. Each input has an individually selectable internal
pullup resistor. Additionally, transition detection allows
seven ports (P24 through P30) to be monitored in any
maskable combination for changes in their logic status.
A detected transition is flagged through an interrupt pin
(port P31).
The Typical Operating Circuit shows two MAX6957s
working together controlling three monocolor 16-seg-
ment-plus-DP displays, with five ports left available for
GPIO (P27–P31 of U2).
The port configuration registers set the 28 ports, P4 to
P31, individually as either LED drivers or GPIO. A pair
of bits in registers 0x09 through 0x0F sets each port’s
configuration (Tables 1 and 2).
The 36-pin MAX6957AAX has 28 ports, P4 to P31. The
28-pin MAX6957ANI and MAX6957AAI make only 20
ports available. The eight unused ports should be con-
figured as outputs on power-up by writing 0x55 to reg-
isters 0x09 and 0x0A. If this is not done, the eight
unused ports remain as floating inputs and quiescent
supply current rises, although there is no damage to
the part.
PIN
NAME FUNCTION
28 SSOP
28 PDIP 36 SSOP 40 TQFN
1 1 36 ISET Segment Current Setting. Connect ISET to GND through a resistor (R
ISET
) to set
the maximum segment current.
2, 3 2, 3 37, 38,
39 GND Ground
4 4 40 DOUT 4-Wire Serial Data Output Port
5–24 — — P12–P31 LED Segment Drivers and GPIO. P12 to P31 can be congured as CA LED drivers,
GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.
—5–32
1–10,
12–19,
21–30
P4–P31 LED Segment Drivers and GPIO. P4 to P31 can be congured as CA LED drivers,
GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.
25 33 32 SCLK 4-Wire Serial Clock Input Port
26 34 33 DIN 4-Wire Serial Data Input Port
27 35 34 CS 4-Wire Chip-Select Input, Active-Low
28 36 35 V+ Positive Supply Voltage. Bypass V+ to GND with a minimum 0.047µF capacitor.
— — 11, 20,
31 N.C. No Connection. Not internally connected.
— — EP EP Exposed Pad. Internally connected to GND. Connect to large ground plane for
maximum thermal dissipation. Do not use as sole ground connection.
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Pin Description
Register Control of I/O Ports and LEDs
Across Multiple Drivers
The MAX6957 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 exam-
ple: seven, 7-segment digits (Figure 2). This example
requires two MAX6957s, with one digit being driven by
both devices, half by one MAX6957, half by the other
(digit 4 in this example). The two drivers are static,
and therefore do not need to be synchronized. The
MAX6957 sees CA digits as multiple discrete LEDs. To
simplify access to displays that overlap two MAX6957s,
the MAX6957 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 decimal
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.
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.
Table 2. Port Configuration Matrix
Table 1. Port Configuration Map
MODE FUNCTION
PORT
REGISTER
(0x20–0x5F)
(0xA0–0xDF)
PIN BEHAVIOR ADDRESS
CODE (HEX)
PORT
CONFIGURATION
BIT PAIR
UPPER LOWER
Output LED Segment Driver
Register bit = 0 High impedance
0x09 to 0x0F 0 0
Register bit = 1
Open-drain current sink, with sink
current (up to 24mA) determined
by the appropriate current register
Output GPIO Output Register bit = 0 Active-low logic output 0x09 to 0x0F 0 1
Active-high logic output
Input GPIO Input
Without Pullup Register bit =
input logic level
Schmitt logic input 0x09 to 0x0F 1 0
Input GPIO Input with Pullup Schmitt logic input with pullup 0x09 to 0x0F 1 1
REGISTER ADDRESS
CODE (HEX)
REGISTER DATA
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
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Shutdown
When the MAX6957 is in shutdown mode, all ports are
forced to inputs, 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 MAX6957 is taken out of shutdown. The display driv-
er 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 6). Shutdown mode is temporarily overridden by
the display test function.
Serial Interface
The MAX6957 communicates through an SPI-compati-
ble 4-wire serial interface. The interface has three
inputs, Clock (SCLK), Chip Select (CS), and Data In
(DIN), and one output, Data Out (DOUT). CS must be
low to clock data into or out of the device, and DIN
must be stable when sampled on the rising edge of
SCLK. DOUT provides a copy of the bit that was input
15.5 clocks earlier, or upon a query it outputs internal
register data, and is stable on the rising edge of SCLK.
Note that the SPI protocol expects DOUT to be high
impedance when the MAX6957 is not being
accessed; DOUT on the MAX6957 is never high imped-
ance. Go to www.maximintegrated.com/an1879 for
ways to convert DOUT to tri-state, if required.
SCLK and DIN may be used to transmit data to other
peripherals, so the MAX6957 ignores all activity on
SCLK and DIN except between the fall and subsequent
rise of CS.
Figure 1. MAX6957 Functional Diagram
D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15
D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15
R/W
8
CEDATA
8
TEST REGISTER
INTENSITY REGISTERS
PORT REGISTERS
LED DRIVERS AND GPIO
INTENSITY
CONFIGURATION
TEST
P4 TO P31
LED DRIVERS
OR GPIO
SEGMENT OR
GPIO DATA R/W
CONFIGURATION
REGISTERS
PORT CHANGE
DETECTOR
MASK REGISTER
COMMAND
REGISTER DECODE
88
DATA BYTE COMMAND BYTE
CS
DIN
SCLK
DOUT
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Figure 3. 4-Wire Interface Timing
Figure 2. Two MAX6957s Controlling Seven 7-Segment Displays
tCSH tCL
tCSS tCH tCSH
CS
SCLK
DIN
DOUT
tDS
tDH
tDV tDO
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
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+
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Control and Operation Using the
4-Wire Interface
Controlling the MAX6957 requires sending a 16-bit word.
The first byte, D15 through D8, is the command address
(Table 3), and the second byte, D7 through D0, is the data
byte (Table 4).
Connecting Multiple MAX6957s
to the 4-Wire Bus
Multiple MAX6957s may be daisy-chained by connect-
ing the DOUT of one device to the DIN of the next, and
driving SCLK and CS lines in parallel (Figure 4). Data at
DIN propagates through the internal shift registers and
appears at DOUT 15.5 clock cycles later, clocked out on
the falling edge of SCLK. When sending commands to
multiple MAX6957s, all devices are accessed at the same
time. An access requires (16 × n) clock cycles, where n is
the number of MAX6957s connected together. To update
just one device in a daisy-chain, the user can send the
No-Op command (0x00) to the others.
Writing Device Registers
The MAX6957 contains a 16-bit shift register into which
DIN data are clocked on the rising edge of SCLK, when
CS is low. When CS is high, transitions on SCLK have no
effect. When CS goes high, the 16 bits in the Shift register
are parallel loaded into a 16-bit latch. The 16 bits in the
latch are then decoded and executed.
The MAX6957 is written to using the following sequence:
1) Take SCLK low.
2) Take CS low. This enables the internal 16-bit shift
register.
3) Clock 16 bits of data into DIN—D15 first, D0 last—
observing the setup and hold times (bit D15 is low,
indicating a write command).
4) Take CS high (either while SCLK is still high after
clocking in the last data bit, or after taking SCLK low).
5) Take SCLK low (if not already low).
Figure 5 shows a write operation when 16 bits are
transmitted.
Figure 5. 16-Bit Write Transmission to the MAX6957
Figure 4. Daisy-Chain Arrangement for Controlling Multiple MAX6957s
.
D15
= 0 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
D15 = 0
CS
SCLK
DIN
DOUT
MICROCONTROLLER
SERIAL DATA OUTPUT
SERIAL CLOCK OUTPUT
SERIAL DATA INPUT
DIN
SCLK
CS
DOUT DIN
SCLK
CS
DOUT DIN
SCLK
CS
DOUT
SERIAL CS OUTPUT MAX6957MAX6957MAX6957
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
It is acceptable to clock more than 16 bits into the
MAX6957 between taking CS low and taking CS high
again. In this case, only the last 16 bits clocked into the
MAX6957 are retained.
Reading Device Registers
Any register data within the MAX6957 may be read by
sending a logic high to bit D15. The sequence is:
1) Take SCLK low.
2) Take CS low (this enables the internal 16-bit shift reg-
ister).
3) Clock 16 bits of data into DIN—D15 first to D0 last.
D15 is high, indicating a read command and bits D14
through D8 containing the address of the register to
be read. Bits D7–D0 contain dummy data, which is
discarded.
4) Take CS high (either while SCLK is still high after
clocking in the last data bit, or after taking SCLK low),
positions D7 through D0 in the Shift register are now
loaded with the register data addressed by bits D1
through D8.
5) Take SCLK low (if not already low).
6) Issue another read or write command (which can
be a No-Op), and examine the bit stream at DOUT;
the second 8 bits are the contents of the register
addressed by bits D1 through D8 in step 3.
Initial Power-Up
On initial power-up, all control registers are reset, cur-
rent registers are set to minimum value, and the
MAX6957 enters shutdown mode (Table 4).
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 one register, 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 configuration register I
bit (Table7). The global current register (0x02) data are
then ignored, and segment currents are set using register
addresses 0x12 through 0x1F (Tables 10, 11, and 12).
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 6). A detected
change is flagged on port P31, which is used as an
active-high interrupt output (INT). Note that the MAX6957
does not identify which specific port(s) caused the inter-
rupt, but provides an alert that one or more port levels
have changed.
The mask register contains 7 mask bits that select which
of the seven ports P24–P30 are to be monitored (Table
13). 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 regard-
less 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.
Port P31 must be configured as an output in order to work
as the interrupt output INT when transition detection is
used. Port P31 is set as output by writing bit D7 = 0 and
bit D6 = 1 to the port configuration register (Table 1).
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 8). Whenever the config-
uration register is written with the M bit set, the MAX6957
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 snap-
shot 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 with the M
bit clear, or a transition is detected. The INT output port
P31 goes low, if it was not already low.
Once transition detection is enabled, the MAX6957 con-
tinuously 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), INT output port P31 is latched high. The INT
output is 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 13).
Transition detection is a one-shot event. When INT has
been cleared after responding to a transition event, tran-
sition 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.
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Table 3. Register Address Map
REGISTER COMMAND ADDRESS HEX
CODE
D15 D14 D13 D12 D11 D10 D9 D8
No-Op R/W 0 0 0 0 0 0 0 0x00
Global Current R/W0 0 0 0 0 1 0 0x02
Configuration R/W0 0 0 0 1 0 0 0x04
Transition Detect Mask R/W0 0 0 0 1 1 0 0x06
Display Test R/W0 0 0 0 1 1 1 0x07
Port Configuration P7, P6, P5, P4 R/W0 0 0 1 0 0 1 0x09
Port Configuration P11, P10, P9, P8 R/W0 0 0 1 0 1 0 0x0A
Port Configuration P15, P14, P13, P12 R/W0 0 0 1 0 1 1 0x0B
Port Configuration P19, P18, P17, P16 R/W0 0 0 1 1 0 0 0x0C
Port Configuration P23, P22, P21, P20 R/W0 0 0 1 1 0 1 0x0D
Port Configuration P27, P26, P25, P24 R/W0 0 0 1 1 1 0 0x0E
Port Configuration P31, P30, P29, P28 R/W0 0 0 1 1 1 1 0x0F
Current054 R/W0 0 1 0 0 1 0 0x12
Current076 R/W0 0 1 0 0 1 1 0x13
Current098 R/W0 0 1 0 1 0 0 0x14
Current0BA R/W0 0 1 0 1 0 1 0x15
Current0DC R/W0 0 1 0 1 1 0 0x16
Current0FE R/W0 0 1 0 1 1 1 0x17
Current110 R/W0 0 1 1 0 0 0 0x18
Current132 R/W0 0 1 1 0 0 1 0x19
Current154 R/W0 0 1 1 0 1 0 0x1A
Current176 R/W0 0 1 1 0 1 1 0x1B
Current198 R/W0 0 1 1 1 0 0 0x1C
Current1BA R/W0 0 1 1 1 0 1 0x1D
Current1DC R/W0 0 1 1 1 1 0 0x1E
Current1FE R/W0 0 1 1 1 1 1 0x1F
Port 0 only (virtual port, no action) R/W0 1 0 0 0 0 0 0x20
Port 1 only (virtual port, no action) R/W0 1 0 0 0 0 1 0x21
Port 2 only (virtual port, no action) R/W0 1 0 0 0 1 0 0x22
Port 3 only (virtual port, no action) R/W0 1 0 0 0 1 1 0x23
Port 4 only (data bit D0. D7–D1 read as 0) R/W0 1 0 0 1 0 0 0x24
Port 5 only (data bit D0. D7–D1 read as 0) R/W0 1 0 0 1 0 1 0x25
Port 6 only (data bit D0. D7–D1 read as 0) R/W0 1 0 0 1 1 0 0x26
Port 7 only (data bit D0. D7–D1 read as 0) R/W0 1 0 0 1 1 1 0x27
Port 8 only (data bit D0. D7–D1 read as 0) R/W0 1 0 1 0 0 0 0x28
Port 9 only (data bit D0. D7–D1 read as 0) R/W0 1 0 1 0 0 1 0x29
Port 10 only (data bit D0. D7–D1 read as 0) R/W0 1 0 1 0 1 0 0x2A
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Table 3. Register Address Map (continued)
REGISTER COMMAND ADDRESS HEX
CODE
D15 D14 D13 D12 D11 D10 D9 D8
Port 11 only (data bit D0. D7–D1 read as 0) R/W0 1 0 1 0 1 1 0x2B
Port 12 only (data bit D0. D7–D1 read as 0) R/W0 1 0 1 1 0 0 0x2C
Port 13 only (data bit D0. D7–D1 read as 0) R/W0 1 0 1 1 0 1 0x2D
Port 14 only (data bit D0. D7–D1 read as 0) R/W0 1 0 1 1 1 0 0x2E
Port 15 only (data bit D0. D7–D1 read as 0) R/W0 1 0 1 1 1 1 0x2F
Port 16 only (data bit D0. D7–D1 read as 0) R/W0 1 1 0 0 0 0 0x30
Port 17 only (data bit D0. D7–D1 read as 0) R/W0 1 1 0 0 0 1 0x31
Port 18 only (data bit D0. D7–D1 read as 0) R/W0 1 1 0 0 1 0 0x32
Port 19 only (data bit D0. D7–D1 read as 0) R/W0 1 1 0 0 1 1 0x33
Port 20 only (data bit D0. D7–D1 read as 0) R/W0 1 1 0 1 0 0 0x34
Port 21 only (data bit D0. D7–D1 read as 0) R/W0 1 1 0 1 0 1 0x35
Port 22 only (data bit D0. D7–D1 read as 0) R/W0 1 1 0 1 1 0 0x36
Port 23 only (data bit D0. D7–D1 read as 0) R/W0 1 1 0 1 1 1 0x37
Port 24 only (data bit D0. D7–D1 read as 0) R/W0 1 1 1 0 0 0 0x38
Port 25 only (data bit D0. D7–D1 read as 0) R/W0 1 1 1 0 0 1 0x39
Port 26 only (data bit D0. D7–D1 read as 0) R/W0 1 1 1 0 1 0 0x3A
Port 27 only (data bit D0. D7–D1 read as 0) R/W0 1 1 1 0 1 1 0x3B
Port 28 only (data bit D0. D7–D1 read as 0) R/W0 1 1 1 1 0 0 0x3C
Port 29 only (data bit D0. D7–D1 read as 0) R/W0 1 1 1 1 0 1 0x3D
Port 30 only (data bit D0. D7–D1 read as 0) R/W0 1 1 1 1 1 0 0x3E
Port 31 only (data bit D0. D7–D1 read as 0) R/W0 1 1 1 1 1 1 0x3F
4 ports 4–7 (data bits D0–D3. D4–D7 read as 0)) R/W1 0 0 0 0 0 0 0x40
5 ports 4–8 (data bits D0–D4. D5–D7 read as 0) R/W1 0 0 0 0 0 1 0x41
6 ports 4–9 (data bits D0–D5. D6–D7 read as 0) R/W1 0 0 0 0 1 0 0x42
7 ports 4–10 (data bits D0–D6. D7 reads as 0) R/W1 0 0 0 0 1 1 0x43
8 ports 4–11 (data bits D0–D7) R/W1 0 0 0 1 0 0 0x44
8 ports 5–12 (data bits D0–D7) R/W1 0 0 0 1 0 1 0x45
8 ports 6–13 (data bits D0–D7) R/W1 0 0 0 1 1 0 0x46
8 ports 7–14 (data bits D0–D7) R/W1 0 0 0 1 1 1 0x47
8 ports 8–15 (data bits D0–D7) R/W1 0 0 1 0 0 0 0x48
8 ports 9–16 (data bits D0–D7) R/W1 0 0 1 0 0 1 0x49
8 ports 10–17 (data bits D0–D7) RW1 0 0 1 0 1 0 0x4A
8 ports 11–18 (data bits D0–D7) R/W1 0 0 1 0 1 1 0x4B
8 ports 12–19 (data bits D0–D7) R/W1 0 0 1 1 0 0 0x4C
8 ports 13–20 (data bits D0–D7) R/W1 0 0 1 1 0 1 0x4D
8 ports 14–21 (data bits D0–D7) R/W1 0 0 1 1 1 0 0x4E
8 ports 15–22 (data bits D0–D7) R/W1 0 0 1 1 1 1 0x4F
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
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 14).
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 tempo-
rarily set to 1/2 the maximum current limit as controlled
by RISET.
Selecting External Component RISET
to Set Maximum Segment Current
The MAX6957 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 in mA.
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 regis-
ter (Table 9) or individual segment current registers
(Tables 10, 11, and 12), according to the setting of the
current control bit of the configuration register (Table 7).
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.
Note: Unused bits read as 0.
Table 3. Register Address Map (continued)
REGISTER COMMAND ADDRESS HEX
CODE
D15 D14 D13 D12 D11 D10 D9 D8
8 ports 16–23 (data bits D0–D7) R/W1 0 1 0 0 0 0 0x50
8 ports 17–24 (data bits D0–D7) R/W1 0 1 0 0 0 1 0x51
8 ports 18–25 (data bits D0–D7) R/W1 0 1 0 0 1 0 0x52
8 ports 19–26 (data bits D0–D7) R/W1 0 1 0 0 1 1 0x53
8 ports 20–27 (data bits D0–D7) R/W1 0 1 0 1 0 0 0x54
8 ports 21–28 (data bits D0–D7) R/W1 0 1 0 1 0 1 0x55
8 ports 22–29 (data bits D0–D7) R/W1 0 1 0 1 1 0 0x56
8 ports 23–30 (data bits D0–D7) R/W1 0 1 0 1 1 1 0x57
8 ports 24–31 (data bits D0–D7) R/W1 0 1 1 0 0 0 0x58
7 ports 25–31 (data bits D0–D6. D7 reads as 0) R/W1 0 1 1 0 0 1 0x59
6 ports 26–31 (data bits D0–D5. D6, D7 read as 0) R/W1 0 1 1 0 1 0 0x5A
5 ports 27–31 (data bits D0–D4. D5–D7 read as 0) R/W1 0 1 1 0 1 1 0x5B
4 ports 28–31 (data bits D0–D3. D4–D7 read as 0) R/W1 0 1 1 1 0 0 0x5C
3 ports 29–31 (data bits D0–D2. D3–D7 read as 0) R/W1 0 1 1 1 0 1 0x5D
2 ports 30–31 (data bits D0–D1. D2–D7 read as 0) R/W1 0 1 1 1 1 0 0x5E
1 port 31 only (data bit D0. D1–D7 read as 0) R/W1 0 1 1 1 1 1 0x5F
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Figure 6. Maskable GPIO Ports P24 Through P31
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
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
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
X = unused bits; if read, zero results.
Table 4. Power-Up Configuration
REGISTER
FUNCTION POWER-UP CONDITION
ADDRESS
CODE
(HEX)
REGISTER DATA
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
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
X = Don’t care bit.
Table 9. Global Segment Current Register Format
X = Don’t care bit.
Table 8. Transition Detection Control (M-Data Bit D7) Format
X = Don’t care bit.
Table 7. Global Current Control (I Data Bit D6) Format
X = Don’t care bit.
Table 6. Shutdown Control (S Data Bit D0) Format
X = Don’t care bit.
Table 5. Configuration 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
FUNCTION ADDRESS CODE
(HEX)
REGISTER DATA
D7 D6 D5 D4 D3 D2 D1 D0
Disabled 0x04 0 I X X X X X S
Enabled 0x04 1 I X X X X X S
FUNCTION ADDRESS
CODE (HEX)
REGISTER DATA
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 X X X X X S
Individual Segment
Constant-current limit for each digit is individually
controlled by the settings in the Current054
through Current1FE registers
0x04 M 1 X X X X X S
FUNCTION ADDRESS CODE
(HEX)
REGISTER DATA
D7 D6 D5 D4 D3 D2 D1 D0
Shutdown 0x04 M I X X X X X 0
Normal Operation 0x04 M I X X X X X 1
FUNCTION ADDRESS CODE
(HEX)
REGISTER DATA
D7 D6 D5 D4 D3 D2 D1 D0
Configuration Register 0x04 M 0 X X X X X S
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Table 10. Individual Segment Current Registers
X = Don’t care bit.
Table 9. Global Segment Current Register Format (continued)
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
LED DRIVE
FRACTION
TYPICAL SEGMENT
CURRENT (mA)
ADDRESS CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
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
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
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 MAX6957 allows each segment’s current to be set
individually from 1/16th (minimum current and LED inten-
sity) to 16/16th (maximum current and LED intensity), as
well as off (zero current). Thus, a bicolor (red-green) seg-
ment 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 MAX6957 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 MAX6957 can sink 28 x 24mA
= 672mA when all outputs are operating as LED segment
drivers at full current. On a 3.3V supply, a MAX6957 dis-
sipates (3.3V - 2.4V) 5 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 MAX6957 absorbs a higher voltage, and the
MAX6957’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 MAX6957
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 5 (82Ω
× 1.02) = 34mW. The maximum MAX6957 dissipation
per LED is at maximum input supply voltage, minimum
toleranced resistance, mini-mum toleranced LED for-
ward-voltage drop, i.e., 0.020 × (5.25V - 2.0V - (0.020A
× 82Ω × 0.98)) = 32.86mW. Worst-case MAX6957 dis-
sipation 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.
Table 11. 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 0 0 0 0 0xX0
2/16 3 0x12 to 0x1F 0 0 0 1 0xX1
3/16 4.5 0x12 to 0x1F 0 0 1 0 0xX2
4/16 6 0x12 to 0x1F 0 0 1 1 0xX3
5/16 7.5 0x12 to 0x1F 0 1 0 0 0xX4
6/16 9 0x12 to 0x1F 0 1 0 1 0xX5
7/16 10.5 0x12 to 0x1F 0 1 1 0 0xX6
8/16 12 0x12 to 0x1F See Table 12. 0 1 1 1 0xX7
9/16 13.5 0x12 to 0x1F 1 0 0 0 0xX8
10/16 15 0x12 to 0x1F 1 0 0 1 0xX9
11/16 16.5 0x12 to 0x1F 1 0 1 0 0xXA
12/16 18 0x12 to 0x1F 1 0 1 1 0xXB
13/16 19.5 0x12 to 0x1F 1 1 0 0 0xXC
14/16 21 0x12 to 0x1F 1 1 0 1 0xXD
15/16 22.5 0x12 to 0x1F 1 1 1 0 0xXE
16/16 24 0x12 to 0x1F 1 1 1 1 0xXF
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18
MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Low-Voltage Operation
The MAX6957 operates down to 2V supply voltage
(although the sourcing and sinking currents are not
guaranteed), providing that the MAX6957 is powered
up initially to at least 2.5V to trigger the device’s internal
reset, and also that the serial interface is constrained to
10Mbps.
Table 14. Display Test Register
X = Don’t care bit.
Table 13. Transition Detection Mask Register
X = Don’t care bit.
Table 12. Odd Individual Segment Current Format
MODE ADDRESS CODE
(HEX)
REGISTER DATA
D7 D6 D5 D4 D3 D2 D1 D0
Normal Operation 0x07 X X X X X X X 0
Display Test Mode 0x07 X X X X X X X 1
FUNCTION
REGISTER
ADDRESS
(HEX)
READ/
WRITE
REGISTER DATA
D7 D6 D5 D4 D3 D2 D1 D0
Mask
Register 0x06
Read 0 Port
30
mask
Port
29
mask
Port
28
mask
Port
27
mask
Port
26
mask
Port
25
mask
Port
24
mask
Write Unchanged
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 0x6X
8/16 12 0x12 to 0x1F 0 1 1 1 See Table 11. 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
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19
MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
SPI Routing Considerations
The MAX6957’s SPI interface is guaranteed to operate at
26Mbps on a 2.5V supply, and on a 5V supply typically
operates at 50Mbps. This means that the transmission
line issues should be considered when the interface con-
nections are longer that 100mm, particularly with higher
supply voltages. Ringing manifests itself as communica-
tion issues, often intermittent, typically due to double
clocking due to ringing at the SCLK input. Fit a 1kΩ to
10kΩ parallel termination resistor to either GND or V+ at
the DIN, SCLK, and CS input to damp ringing for moder-
ately long interface runs. Use line impedance matching
terminations when making connections between boards.
PC Board Layout Considerations
Ensure that all the MAX6957 GND connections are
used. A ground plane is not necessary, but may be
useful to reduce supply impedance if the MAX6957
outputs are to be heavily loaded. Keep the track length
from the ISET pin to the RISET resistor as short as pos-
sible, and take the GND end of the resistor either to the
ground plane or directly to the GND pins.
Power-Supply Considerations
The MAX6957 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 MAX6957 is far away from the
board’s input bulk decoupling capacitor.
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+
CS
DIN
SCLK
P4
P31
P26
P5
P30
P6
P29
P7
P28
P27
P17
P16
P15
P11
P14
P10
P13
P9
P12
P8
DOUT
GND
GND
ISET
SSOP
TOP VIEW
MAX6957
22
21
20
19
15
16
17
18 P22
P25
P24
P23
P21
P20
P19
P18
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+
CS
DIN
SCLK
N.C.
DOUT
TQFN
MAX6957
P24
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│
20
MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Pin Congurations (continued)
Chip Information
PROCESS: CMOS
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
33
35
34
4
29
27
31
24
25
22
21
23
V+
GND
ISET
GND
SCLK
DIN
DOUT
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
CS MAX6957AAX
39kΩ
3V
3V
4-WIRE DATA IN
4-WIRE CLOCK IN
CHIP SELECT
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
33
35
34
4
29
27
31
24
25
22
21
23
V+
GND
ISET
GND
SCLK
DIN
DOUT
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
CS MAX6957AAX
39kΩ
3V
4-WIRE DATA OUT
IRQ OUT
LED3
a2
a1
c
d1
b
e
d2
g1
g2
f
i
h
k
l
j
dp
m
ca
LED2
U1
U2
21 2
SW3
SW2SW1
47nF
47nF
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21
MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Typical Operating Circuit
PACKAGE TYPE PACKAGE CODE DOCUMENT NO. LAND PATTERN NO.
28 PDIP N28-2 21-0043 —
28 SSOP A28-1 21-0056 90-0095
36 SSOP A36-4 21-0040 90-0098
40 TQFN-EP
T4066+5 21-0141 90-0055
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│
22
MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 4/02 Initial Release —
1 10/02 Corrected data sheet 1, 3, 5, 9, 10, 11, 14, 19
2 2/03 Revised Electrical Characteristics table and added QFN package 1, 3
3 11/03 Package change, added new sections 1, 5-7, 10-14, 18,
20, 24 25
4 2/07
Added exposed pad information to Genaral Description, package code to
Ordering Information, corrected Absolute Maximum Ratings, TQFN pinout
information to Pin Description
1, 2, 5
5 7/14 Removed automotive reference from data sheet 1
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2014 Maxim Integrated Products, Inc.
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23
MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
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