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
Automotive
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
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
________________________________________________________________ Maxim Integrated Products 1
28
27
26
25
24
23
22
21
20
19
18
17
16
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
V+
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
Pin Configurations
19-2429; Rev 4; 2/07
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Typical Operating Circuit appears at end of data sheet.
Ordering Information
PART TEMP RANGE PIN-
PACKAGE
PKG
CODE
MAX6957ANI -40°C to +125°C 28 DIP N28-2
MAX6957AAI -40°C to +125°C 28 SSOP A28-1
MAX6957AAX -40°C to +125°C 36 SSOP A36-4
MAX6957ATL -40°C to +125°C 40 Thin QFN T4066-5
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corp. Pin Configurations continued at end of data sheet.
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage (with Respect to GND)
V+ .............................................................................-0.3V to +6V
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
ELECTRICAL CHARACTERISTICS
(Typical Operating Circuit, V+ = 2.5V to 5.5V, TA= TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Operating Supply Voltage V+ 2.5 5.5 V
TA = +25°C 5.5 8
TA = - 40°C to + 85°C 10Shutdown Supply Current ISHDN Al l d i g i tal i np uts at
V + or G N D
TA = TMIN to TMAX 11
µA
TA = +25°C 180 230
TA = - 40°C to + 85°C 250Operating Supply Current IGPOH
Al l p or ts p r og r am m ed
as outp uts hi g h, no l oad ,
al l other i np uts at V + or
G N D TA = TMIN to TMAX 270
µA
TA = +25°C 170 210
TA = - 40°C to + 85°C 230
Operating Supply Current IGPOL
Al l p or ts p r og r am m ed
as outp uts l ow , no l oad ,
al l other i np uts at V + or
G N D TA = TMIN to TMAX 240
µA
TA = +25°C 110 135
TA
= - 40° C to + 85°C 140Operating Supply Current ILED
Al l p or ts p r og r am m ed
as LE D outp uts, al l LE D s
off, no l oad , al l other
i np uts at V + or G N D TA = TMIN to TMAX 145
µA
INPUTS AND OUTPUTS
Logic-High Input Voltage
Port Inputs VIH 0.7 ✕
V+ V
Logic-Low Input Voltage
Port Inputs VIL 0.3 ✕
V+ V
Input Leakage Current IIH, IIL GPIO inputs without pullup,
VPORT = V+ to GND -100 ±1 +100 nA
V+ = 2.5V 12 19 30
GPIO Input Internal Pullup to V+ IPU V+ = 5.5V 80 120 180 µA
Hysteresis Voltage GPIO Inputs ΔVI0.3 V
GPIO outputs, ISOURCE = 2mA, TA = -40°C to
+85°C
V+ -
0.7 V
Output High Voltage VOH GPIO outputs, ISOURCE = 1mA,
TA = TMIN to TMAX (Note 2)
V+ -
0.7 V
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
_______________________________________________________________________________________ 3
Note 1: All parameters tested at TA= +25°C. Specifications over temperature are guaranteed by design.
Note 2: Guaranteed by design.
ELECTRICAL CHARACTERISTICS (continued)
(Typical Operating Circuit, V+ = 2.5V to 5.5V, TA= TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Port Sink Current IOL VPORT = 0.6V 2 10 18 mA
Output Short-Circuit Current IOLSC Port configured output low, shorted to V+ 2.75 11 20 mA
V+ = 2.5V, VLED = 2.3V at maximum LED
current 9.5 13.5 18
V+ = 3.3V, VLED = 2.4V at maximum LED
current (Note 2) 18.5 24 27.5
Port Drive LED Sink Current,
Port Configured as LED Driver IPORT
V+ = 5.5V, VLED = 2.4V at maximum LED
current 19 25 30
mA
V+ = 2.5V, VOUT = 0.6V at maximum LED
current 18.5 23 28.0
Port Drive Logic Sink Current,
Port Configured as LED Driver IPORT_SC V+ = 5.5V, VOUT = 0.6V at maximum LED
current 19 24 28
mA
Port LED Sink Current Matching ΔIPORT 6%
V+ ≤ 3.3V 1.6
Input High-Voltage SCLK, DIN,
CS VIH V+ > 3.3V 2 V
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
TIMING CHARACTERISTICS (Figure 3)
(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 0ns
DIN Setup Time tDS 9.5 ns
DIN Hold Time tDH 0ns
Output Data Propagation Delay tDO CLOAD = 25pF 21 ns
Minimum CS Pulse High tCSW 19 ns
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
4 _______________________________________________________________________________________
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)
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX6957 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (μA)
97.570.042.515.0-12.5
4
5
6
7
8
3
-40.0 125.0
V+ = 5.5V
V+ = 3.3V
V+ = 2.5V
OPERATING SUPPLY CURRENT vs. V+
(NO LOADS)
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)
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
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
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
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
GPI PULLUP CURRENT
vs. TEMPERATURE
MAX6957 toc08
TEMPERATURE (°C)
PULLUP CURRENT (μA)
97.570.042.515.0-12.5
100
1000
10
-40.0 125.0
V+ = 5.5V
V+ = 3.3V
V+ = 2.5V
GPO SHORT-CIRCUIT CURRENT
vs. TEMPERATURE
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
__________________________________________Typical Operating Characteristics
(RISET = 39kΩ, TA = +25°C, unless otherwise noted.)
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 config-
ured 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 seg-
ments with individual 16-step adjustment of the con-
stant current through each LED segment. A single
resistor sets the maximum segment current for all seg-
ments, 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 (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 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.
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
_______________________________________________________________________________________ 5
PIN
28 SSOP
28 DIP
36
SSOP
40
TQFN
NAME FUNCTION
1 1 36 ISET Segment Current Setting. Connect ISET to GND through a resistor (RISET) to set
the maximum segment current.
2, 3 2, 3 37, 38,
39 GND Ground
4 4 40 DOUT 4-Wire Serial Data Output Port
5–24 — — P12–P31 LED Segment Drivers and GPIO. P12 to P31 can be configured as CA LED drivers,
GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.
— 5–32
1–10,
12–19,
21–30
P4–P31 LED Segment Drivers and GPIO. P4 to P31 can be configured as CA LED drivers,
GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.
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 Paddle. Internally connected to GND. Connect to large ground plane for
maximum thermal dissipation. Do not use as sole ground connection.
Pin Description
MAX6957
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 example:
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 deci-
mal point can be updated in a single byte-write, a 14-
segment digit with DP can be updated in two
byte-writes, and 16-segment digits with DP can be
updated in two byte-writes plus a bit write. Also, dis-
crete LEDs and GPIO port bits can be lit and controlled
individually without affecting other ports.
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
6 _______________________________________________________________________________________
Table 1. Port Configuration Map
REGISTER DATA
REGISTER ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
Port Configuration for P7, P6, P5, P4 0x09 P7 P6 P5 P4
Port Configuration for P11, P10, P9, P8 0x0A P11 P10 P9 P8
Port Configuration for P15, P14, P13, P12 0x0B P15 P14 P13 P12
Port Configuration for P19, P18, P17, P16 0x0C P19 P18 P17 P16
Port Configuration for P23, P22, P21, P20 0x0D P23 P22 P21 P20
Port Configuration for P27, P26, P25, P24 0x0E P27 P26 P25 P24
Port Configuration for P31, P30, P29, P28 0x0F P31 P30 P29 P28
Table 2. Port Configuration Matrix
Note: The logic is inverted between the two output modes; a high makes the output go low in LED segment driver mode (0x00) to
turn that segment on; in GPIO output mode (0x01), a high makes the output go high.
PORT
CONFIGURATION
BIT PAIR
MODE FUNCTION
PORT
REGISTER
(0x20–0x5F)
(
0xA0–0xDF
)
PIN BEHAVIOR ADDRESS
CODE
(
HEX
)
UPPER LOWER
Register bit = 0 High impedance
Output LED Segment Driver Register bit = 1
Open-drain current sink, with sink
current (up to 24mA) determined
by the appropriate current register
0x09 to 0x0F 0 0
Active-low logic output
Output GPIO Output Register bit = 0 Active-high logic output 0x09 to 0x0F 0 1
Input GPIO Input
Without Pullup Schmitt logic input 0x09 to 0x0F 1 0
Input GPIO Input with
Register bit =
input logic level Schmitt logic input with pullup 0x09 to 0x0F 1 1
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 driver can still be programmed while in
shutdown mode. For minimum supply current in shut-
down 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
impedance. Go to www.maxim-ic.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.
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
_______________________________________________________________________________________ 7
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
Figure 1. MAX6957 Functional Diagram
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Figure 2. Two MAX6957s Controlling Seven 7-Segment Displays
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+
Figure 3. 4-Wire Interface Timing
tCSH tCL
tCSS tCH tCSH
CS
SCLK
DIN
DOUT
tDS
tDH
tDV tDO
8 _______________________________________________________________________________________
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 togeth-
er. 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.
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
_______________________________________________________________________________________ 9
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
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
Figure 5. 16-Bit Write Transmission to the MAX6957
MAX6957
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
register).
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 regis-
ter 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 regis-
ter, sets the current for all ports configured as LED seg-
ment drivers. It is also possible to individually control
the current drive of each LED segment driver.
Individual/global brightness control is selected by set-
ting the configuration register I bit (Table7). The global
current register (0x02) data are then ignored, and seg-
ment 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 interrupt, 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 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.
Port P31 must be configured as an output in order to
work as the interrupt output INT when transition detec-
tion 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 regis-
ter 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 configuration register is written with the M bit set,
the MAX6957 updates an internal 7-bit snapshot regis-
ter, which holds the comparison copy of the logic states
of ports P24 through P30. The update action occurs
regardless of the previous state of the M bit, so that it is
not necessary to clear the M bit and then set it again to
update the snapshot register.
When the configuration register is written with the M bit
set, transition detection is enabled and remains
enabled until either the configuration register is written
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
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), 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 condi-
tion. 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,
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.
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
10 ______________________________________________________________________________________
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 11
Table 3. Register Address Map
COMMAND ADDRESS
REGISTER D15 D14 D13 D12 D11 D10 D9 D8
HEX
CODE
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
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
12 ______________________________________________________________________________________
COMMAND ADDRESS
REGISTER D15 D14 D13 D12 D11 D10 D9 D8
HEX
CODE
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) R/ W1 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
Table 3. Register Address Map (continued)
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 temporarily 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 register
(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 cur-
rent. The current difference between successive cur-
rent steps, ISTEP, is therefore determined by the
formula:
ISTEP = ISEG / 16
If ISEG = 24mA, then ISTEP = 24mA / 16 = 1.5mA.
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 13
COMMAND ADDRESS
REGISTER D15 D14 D13 D12 D11 D10 D9 D8
HEX
CODE
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
Table 3. Register Address Map (continued)
Note: Unused bits read as 0.
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
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
Figure 6. Maskable GPIO Ports P24 Through P31
14 ______________________________________________________________________________________
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 15
Table 4. Power-Up Configuration
REGISTER DATA
REGISTER
FUNCTION POWER-UP CONDITION
ADDRESS
CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Port Register
Bits 4 to 31 LED Off; GPIO Output Low 0x24 to
0x3F XXXXXXX0
Global
Current 1/16 (minimum on) 0x02 X X X X 0 0 0 0
Configuration
Register
Shutdown Enabled
Current Control = Global
Transition Detection Disabled
0x04 0 0 X X X X X 0
Input Mask
Register All Clear (Masked Off) 0x06 X 0 0 0 0 0 0 0
Display Test Normal Operation 0x07 X X X X X X X 0
Port
Configuration P7, P6, P5, P4: GPIO Inputs Without Pullup 0x09 1 0 1 0 1 0 1 0
Port
Configuration P11, P10, P9, P8: GPIO Inputs Without Pullup 0x0A 1 0 1 0 1 0 1 0
Port
Configuration P15, P14, P13, P12: GPIO Inputs Without Pullup 0x0B 1 0 1 0 1 0 1 0
Port
Configuration P19, P18, P17, P16: GPIO Inputs Without Pullup 0x0C 1 0 1 0 1 0 1 0
Port
Configuration P23, P22, P21, P20: GPIO Inputs Without Pullup 0x0D 1 0 1 0 1 0 1 0
Port
Configuration P27, P26, P25, P24: GPIO Inputs Without Pullup 0x0E 1 0 1 0 1 0 1 0
Port
Configuration P31, P30, P29, P28: GPIO Inputs Without Pullup 0x0F 1 0 1 0 1 0 1 0
Current054 1/16 (minimum on) 0x12 0 0 0 0 0 0 0 0
Current076 1/16 (minimum on) 0x13 0 0 0 0 0 0 0 0
Current098 1/16 (minimum on) 0x14 0 0 0 0 0 0 0 0
Current0BA 1/16 (minimum on) 0x15 0 0 0 0 0 0 0 0
Current0DC 1/16 (minimum on) 0x16 0 0 0 0 0 0 0 0
Current0FE 1/16 (minimum on) 0x17 0 0 0 0 0 0 0 0
Current110 1/16 (minimum on) 0x18 0 0 0 0 0 0 0 0
Current132 1/16 (minimum on) 0x19 0 0 0 0 0 0 0 0
Current154 1/16 (minimum on) 0x1A 0 0 0 0 0 0 0 0
Current176 1/16 (minimum on) 0x1B 0 0 0 0 0 0 0 0
Current198 1/16 (minimum on) 0x1C 0 0 0 0 0 0 0 0
Current1BA 1/16 (minimum on) 0x1D 0 0 0 0 0 0 0 0
Current1DC 1/16 (minimum on) 0x1E 0 0 0 0 0 0 0 0
Current1FE 1/16 (minimum on) 0x1F 0 0 0 0 0 0 0 0
X = unused bits; if read, zero results.
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
16 ______________________________________________________________________________________
Table 5. Configuration Register Format
REGISTER DATA
FUNCTION ADDRESS CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Configuration Register 0x04 M I XXXXXS
Table 6. Shutdown Control (S Data Bit D0) Format
REGISTER DATA
FUNCTION ADDRESS CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Shutdown 0x04 M I XXXXX0
Normal Operation 0x04 M I XXXXX1
REGISTER DATA
FUNCTION ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
Global
Constant-current limits for all digits are
controlled by one setting in the Global Current
register, 0x02
0x04 M 0 XXXXXS
Individual Segment
Constant-current limit for each digit is
individually controlled by the settings in the
Current054 through Current1FE registers
0x04 M 1 XXXXXS
Table 7. Global Current Control (I Data Bit D6) Format
Table 8. Transition Detection Control (M-Data Bit D7) Format
REGISTER DATA
FUNCTION ADDRESS CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Disabled 0x04 0 I XXXXXS
Enabled 0x04 1 I XXXXXS
Table 9. Global Segment Current Register Format
LED DRIVE
FRACTION
TYPICAL SEGMENT
CURRENT (mA)
ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
1/16 1.5 0x02 X X X X 0 0 0 0 0xX0
2/16 3 0x02 X X X X 0 0 0 1 0xX1
3/16 4.5 0x02 X X X X 0 0 1 0 0xX2
4/16 6 0x02 X X X X 0 0 1 1 0xX3
5/16 7.5 0x02 X X X X 0 1 0 0 0xX4
X = Don’t care bit.
X = Don’t care bit.
X = Don’t care bit.
X = Don’t care bit.
X = Don’t care bit.
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 17
Table 9. Global Segment Current Register Format (continued)
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
X = Don’t care bit.
Table 10. Individual Segment Current Registers
REGISTER
FUNCTION
ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
Current054 register 0x12 Segment 5 Segment 4
Current076 register 0x13 Segment 7 Segment 6
Current098 register 0x14 Segment 9 Segment 8
Current0BA register 0x15 Segment 11 Segment 10
Current0DC register 0x16 Segment 13 Segment 12
Current0FE register 0x17 Segment 15 Segment 14
Current110 register 0x18 Segment 17 Segment 16
Current132 register 0x19 Segment 19 Segment 18
Current154 register 0x1A Segment 21 Segment 20
Current176 register 0x1B Segment 23 Segment 22
Current198 register 0x1C Segment 25 Segment 24
Current1BA register 0x1D Segment 27 Segment 26
Current1DC register 0x1E Segment 29 Segment 28
Current1FE register 0x1F Segment 31 Segment 30
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
18 ______________________________________________________________________________________
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 cur-
rent to be set individually from 1/16th (minimum current
and LED intensity) to 16/16th (maximum current and
LED intensity), as well as off (zero current). Thus, a
bicolor (red-green) segment pair can be set to 289
color/intensity combinations. A discrete or CA tricolor
(red-green-yellow or red-green-blue) segment triad can
be set to 4913 color/intensity combinations.
Power Dissipation Issues
Each 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 seg-
ment drivers at full current. On a 3.3V supply, a
MAX6957 dissipates (3.3V - 2.4V) ✕672mA = 0.6W
when driving 28 of these 2.4V forward-voltage drop
LEDs at full current. This dissipation is within the ratings
of the 36-pin SSOP package with an ambient tempera-
ture up to +98°C. If a higher supply voltage is used or
the LEDs used have a lower forward-voltage drop than
2.4V, the 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✕(82Ω
✕ 1.02) = 34mW. The maximum MAX6957 dissipation
per LED is at maximum input supply voltage, minimum
toleranced resistance, minimum toleranced LED for-
ward-voltage drop, i.e., 0.020 x (5.25V - 2.0V - (0.020A
✕82Ωx 0.98)) = 32.86mW. Worst-case MAX6957 dissi-
pation is 920mW, driving all 28 LEDs at 20mA full cur-
rent at once, which meets the 941mW dissipation
ratings of the 36-pin SSOP package.
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 0000 0xX0
2/16 3 0x12 to 0x1F 0001 0xX1
3/16 4.5 0x12 to 0x1F 0010 0xX2
4/16 6 0x12 to 0x1F 0011 0xX3
5/16 7.5 0x12 to 0x1F 0100 0xX4
6/16 9 0x12 to 0x1F 0101 0xX5
7/16 10.5 0x12 to 0x1F 0110 0xX6
8/16 12 0x12 to 0x1F See Table 12. 0111 0xX7
9/16 13.5 0x12 to 0x1F 1000 0xX8
10/16 15 0x12 to 0x1F 1001 0xX9
11/16 16.5 0x12 to 0x1F 1010 0xXA
12/16 18 0x12 to 0x1F 1011 0xXB
13/16 19.5 0x12 to 0x1F 1100 0xXC
14/16 21 0x12 to 0x1F 1101 0xXD
15/16 22.5 0x12 to 0x1F 1110 0xXE
16/16 24 0x12 to 0x1F 1111 0xXF
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 19
REGISTER DATA
FUNCTION
REGISTER
ADDRESS
(HEX)
READ/
WRITE D7 D6 D5 D4 D3 D2 D1 D0
Read 0
Mask
Register 0x06
Write Unchanged
Port
30
mask
Port
29
mask
Port
28
mask
Port
27
mask
Port
26
mask
Port
25
mask
Port
24
mask
REGISTER DATA
MODE ADDRESS CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Normal Operation 0x07 XXXXXXX0
Display Test Mode 0x07 XXXXXXX1
X = Don’t care bit.
Table 12. Odd Individual Segment Current Format
LED
DRIVE
FRACTION
SEGMENT
CONSTANT
CURRENT WITH
RISET = 39kΩ (mA)
ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
1/16 1.5 0x12 to 0x1F 0 0 0 0 0x0X
2/16 3 0x12 to 0x1F 0 0 0 1 0x1X
3/16 4.5 0x12 to 0x1F 0 0 1 0 0x2X
4/16 6 0x12 to 0x1F 0 0 1 1 0x3X
5/16 7.5 0x12 to 0x1F 0 1 0 0 0x4X
6/16 9 0x12 to 0x1F 0 1 0 1 0x5X
7/16 10.5 0x12 to 0x1F 0 1 1 0 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
Table 13. Transition Detection Mask Register
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.
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
20 ______________________________________________________________________________________
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
Pin Configurations (continued)
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 1kΩto
10kΩparallel 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.
Chip Information
TRANSISTOR COUNT: 30,316
PROCESS: CMOS
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 21
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
212
SW3
SW2SW1
47nF
47nF
Typical Operating Circuit
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
22 ______________________________________________________________________________________
SSOP.EPS
PACKAGE OUTLINE, SSOP, 5.3 MM
1
1
21-0056 C
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
NOTES:
1. D&E DO NOT INCLUDE MOLD FLASH.
2. MOLD FLASH OR PROTRUSIONS NOT TO EXCEED .15 MM (.006").
3. CONTROLLING DIMENSION: MILLIMETERS.
4. MEETS JEDEC MO150.
5. LEADS TO BE COPLANAR WITHIN 0.10 MM.
7.90
H
L
0∞
0.301
0.025
8∞
0.311
0.037
0∞
7.65
0.63
8∞
0.95
MAX
5.38
MILLIMETERS
B
C
D
E
e
A1
DIM
A
SEE VARIATIONS
0.0256 BSC
0.010
0.004
0.205
0.002
0.015
0.008
0.212
0.008
INCHES
MIN MAX
0.078
0.65 BSC
0.25
0.09
5.20
0.05
0.38
0.20
0.21
MIN
1.73 1.99
MILLIMETERS
6.07
6.07
10.07
8.07
7.07
INCHES
D
D
D
D
D
0.239
0.239
0.397
0.317
0.278
MIN
0.249
0.249
0.407
0.328
0.289
MAX MIN
6.33
6.33
10.33
8.33
7.33
14L
16L
28L
24L
20L
MAX N
A
D
eA1 L
C
HE
N
12
B
0.068
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
______________________________________________________________________________________ 23
SSOP.EPS
PACKAGE OUTLINE, 36L SSOP, 0.80 MM PITCH
1
1
21-0040 E
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
FRONT VIEW
MAX
0.011
0.104
0.017
0.299
0.013
INCHES
0.291
0.009
E
C
DIM
0.012
0.004
B
A1
MIN
0.096A
0.23
7.40 7.60
0.32
MILLIMETERS
0.10
0.30
2.44
MIN
0.44
0.29
MAX
2.65
0.040
0.020L0.51 1.02
H 0.4140.398 10.11 10.51
e 0.0315 BSC 0.80 BSC
D 0.6120.598 15.20 15.55
HE
A1 A
D
eB0∞-8∞
L
C
TOP VIEW
SIDE VIEW
1
36
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
24 ______________________________________________________________________________________
QFN THIN.EPS
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX6957
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 25
© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
Revision History
Pages changed at Rev 4: 1, 2, 5, 20, 24, 25
