19-2429; Rev 4; 2/07

4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and

28-Port LED Display Driver and I/O Expander
General Description Features

MAX6957
The MAX6957 compact, serial-interfaced LED display ♦ High-Speed 26MHz SPI-/QSPI-™/MICROWIRE™-
driver general-purpose I/O (GPIO) peripheral provides Compatible Serial Interface
microprocessors with up to 28 ports. Each port is indi-
♦ 2.5V to 5.5V Operation
vidually user configurable to either a logic input, logic
output, or common-anode (CA) LED constant-current ♦ -40°C to +125°C Temperature Range
segment driver. Each port configured as an LED seg- ♦ 20 or 28 I/O Ports, Each Configurable as
ment driver behaves as a digitally controlled constant- Constant-Current LED Driver
current sink, with 16 equal current steps from 1.5mA to Push-Pull Logic Output
24mA. The LED drivers are suitable for both discrete
Schmitt Logic Input
LEDs and CA numeric and alphanumeric LED digits.
Schmitt Logic Input with Internal Pullup
Each port configured as a GPIO can be either a push-
pull logic output capable of sinking 10mA and sourcing ♦ 11µA (max) Shutdown Current
4.5mA, or a Schmitt logic input with optional internal ♦ 16-Step Individually Programmable Current
pullup. Seven ports feature configurable transition Control for Each LED
detection logic, which generates an interrupt upon ♦ Logic Transition Detection for Seven I/O Ports
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 Ordering Information
are available in 36-pin SSOP and 40-pin TQFN (6mm x PIN- PKG
6mm) packages, respectively. The MAX6957AAI and PART TEMP RANGE
PACKAGE CODE
MAX6957ANI have 20 ports and are available in 28-pin
SSOP and 28-pin DIP packages, respectively. MAX6957ANI -40°C to +125°C 28 DIP N28-2

For a 2-wire interfaced version, refer to the MAX6956 MAX6957AAI -40°C to +125°C 28 SSOP A28-1
data sheet. MAX6957AAX -40°C to +125°C 36 SSOP A36-4
For a lower cost pin-compatible port expander without MAX6957ATL -40°C to +125°C 40 Thin QFN T4066-5
the constant-current LED drive capability, refer to the
MAX7301 data sheet.
Pin Configurations
Applications TOP VIEW
Set-Top Boxes ISET 1 28 V+
Panel Meters GND 2 27 CS
White Goods GND 3 26 DIN

Automotive DOUT 4 25 SCLK

P12 5 24 P31
Bar Graph Displays
P13 6 23 P30
Industrial Controllers
P14 7 MAX6957 22 P29
System Monitoring
P15 8 21 P28

P16 9 20 P27

P17 10 19 P26

P18 11 18 P25

P19 12 17 P24

P20 13 16 P23
Typical Operating Circuit appears at end of data sheet. P21 14 15 P22

SSOP/DIP
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corp. Pin Configurations continued at end of data sheet.

________________________________________________________________ Maxim Integrated Products 1

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.
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
ABSOLUTE MAXIMUM RATINGS
MAX6957

Voltage (with Respect to GND) Operating Temperature Range (TMIN, TMAX) ....-40°C to +125°C
V+ .............................................................................-0.3V to +6V Junction Temperature ......................................................+150°C
All Other pins................................................-0.3V to (V+ + 0.3V) Storage Temperature Range .............................-65°C to +150°C
P4–P31 Current ................................................................±30mA Lead Temperature (soldering, 10s) .................................+300°C
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

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS
(Typical Operating Circuit, V+ = 2.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Operating Supply Voltage V+ 2.5 5.5 V
TA = +25°C 5.5 8
ISHDN All digital inputs at
Shutdown Supply Current TA = -40°C to +85°C 10 µA
V+ or GND
TA = TMIN to TMAX 11
All ports programmed TA = +25°C 180 230
as outputs high, no load,
Operating Supply Current IGPOH TA = -40°C to +85°C 250 µA
all other inputs at V+ or
GND TA = TMIN to TMAX 270
All ports programmed TA = +25°C 170 210
as outputs low, no load,
Operating Supply Current IGPOL TA = -40°C to +85°C 230 µA
all other inputs at V+ or
GND TA = TMIN to TMAX 240
All ports programmed TA = +25°C 110 135
as LED outputs, all LEDs
Operating Supply Current ILED TA = -40°C to +85°C 140 µA
off, no load, all other
inputs at V+ or GND TA = TMIN to TMAX 145
INPUTS AND OUTPUTS
Logic-High Input Voltage 0.7 ✕
VIH V
Port Inputs V+
Logic-Low Input Voltage 0.3 ✕
VIL V
Port Inputs V+
GPIO inputs without pullup,
Input Leakage Current IIH, IIL -100 ±1 +100 nA
VPORT = V+ to GND
V+ = 2.5V 12 19 30
GPIO Input Internal Pullup to V+ IPU µA
V+ = 5.5V 80 120 180
Hysteresis Voltage GPIO Inputs ΔVI 0.3 V
GPIO outputs, ISOURCE = 2mA, TA = -40°C to V+ -
V
+85°C 0.7
Output High Voltage VOH
GPIO outputs, ISOURCE = 1mA, V+ -
V
TA = TMIN to TMAX (Note 2) 0.7

2 _______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
ELECTRICAL CHARACTERISTICS (continued)

MAX6957
(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
9.5 13.5 18
current
Port Drive LED Sink Current, V+ = 3.3V, VLED = 2.4V at maximum LED
IPORT 18.5 24 27.5 mA
Port Configured as LED Driver current (Note 2)
V+ = 5.5V, VLED = 2.4V at maximum LED
19 25 30
current
V+ = 2.5V, VOUT = 0.6V at maximum LED
18.5 23 28.0
Port Drive Logic Sink Current, current
IPORT_SC mA
Port Configured as LED Driver V+ = 5.5V, VOUT = 0.6V at maximum LED
19 24 28
current
Port LED Sink Current Matching ΔIPORT 6 %
Input High-Voltage SCLK, DIN, V+ ≤ 3.3V 1.6
VIH V
CS V+ > 3.3V 2
Input Low-Voltage SCLK, DIN, CS VIL 0.6 V
Input Leakage Current SCLK,
IIH, IIL -50 +50 nA
DIN, CS
V+ -
Output High-Voltage DOUT VOH ISOURCE = 1.6mA V
0.5
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 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

Note 1: All parameters tested at TA = +25°C. Specifications over temperature are guaranteed by design.
Note 2: Guaranteed by design.

_______________________________________________________________________________________ 3
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
MAX6957

__________________________________________Typical Operating Characteristics

(RISET = 39kΩ, TA = +25°C, unless otherwise noted.)

OPERATING SUPPLY CURRENT SHUTDOWN SUPPLY CURRENT OPERATING SUPPLY CURRENT vs. V+
vs. TEMPERATURE vs. TEMPERATURE (NO LOADS)
0.40 8 100

MAX6957 toc03
MAX6957 toc02
V+ = 2.5V TO 5.5V MAX6957 toc01
0.36 ALL PORTS LED (ON)
NO LOAD V+ = 5.5V
0.32 7
10

SUPPLY CURRENT (mA)

SUPPLY CURRENT (μA)
SUPPLY CURRENT (mA)

0.28 ALL PORTS V+ = 3.3V

ALL PORTS OUTPUT (0) ALL PORTS OUTPUT (1)
0.24 OUTPUT (1) 6
0.20 1
ALL PORTS OUTPUT (0)
0.16 5 V+ = 2.5V
0.12
0.1
0.08 4
0.04 ALL PORTS LED (OFF) ALL PORTS LED (OFF)
0 3 0.01
-40.0 -12.5 15.0 42.5 70.0 97.5 125.0 -40.0 -12.5 15.0 42.5 70.0 97.5 125.0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
TEMPERATURE (°C) TEMPERATURE (°C) V+ (V)

LED DRIVER SINK CURRENT GPO SINK CURRENT vs. TEMPERATURE

LED DRIVER SINK CURRENT vs. V+ vs. TEMPERATURE (OUTPUT = 0)
26 27 18
MAX6957 toc05

MAX6957 toc06
MAX6957 toc04

VLED = 2.4V V+ = 2.5V TO 5.5V, VPORT = 0.6V

24 26 16
22 V+ = 5.5V
PORT SINK CURRENT (mA)

PORT SINK CURRENT (mA)

PORT SINK CURRENT (mA)

14
25
20
LED DROP = 2.4V 12
18 24
16 10
23
14 LED DROP = 1.8V 8
V+ = 3.3V
12 22
6
10
21 4
8
6 20 2
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -40.0 -12.5 15.0 42.5 70.0 97.5 125.0 -40.0 -12.5 15.0 42.5 70.0 97.5 125.0
V+ (V) TEMPERATURE (°C) TEMPERATURE (°C)

GPO SOURCE CURRENT vs. TEMPERATURE GPI PULLUP CURRENT GPO SHORT-CIRCUIT CURRENT
(OUTPUT = 1) vs. TEMPERATURE vs. TEMPERATURE
9 1000 100
MAX6957 toc07

MAX6957 toc08

MAX6957 toc09

VPORT = 1.4V
8
PORT SOURCE CURRENT (mA)

V+ = 5.5V
PULLUP CURRENT (μA)

7
PORT CURRENT (mA)

V+ = 5.5V GPO = 0, PORT

V+ = 3.3V SHORTED TO V+
6
100 10
5 V+ = 2.5V V+ = 3.3V

4
V+ = 2.5V GPO = 1, PORT
3
SHORTED TO GND
2 10 1
-40.0 -12.5 15.0 42.5 70.0 97.5 125.0 -40.0 -12.5 15.0 42.5 70.0 97.5 125.0 -40.0 -12.5 15.0 42.5 70.0 97.5 125.0
TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C)

4 _______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Pin Description

MAX6957
PIN
28 SSOP 36 40 NAME FUNCTION
28 DIP SSOP TQFN

Segment Current Setting. Connect ISET to GND through a resistor (RISET) to set
1 1 36 ISET
the maximum segment current.
37, 38,
2, 3 2, 3 GND Ground
39
4 4 40 DOUT 4-Wire Serial Data Output Port
LED Segment Drivers and GPIO. P12 to P31 can be configured as CA LED drivers,
5–24 — — P12–P31
GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.
1–10,
LED Segment Drivers and GPIO. P4 to P31 can be configured as CA LED drivers,
— 5–32 12–19, P4–P31
GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.
21–30
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,
— — N.C. No Connection. Not internally connected.
31
Exposed Paddle. Internally connected to GND. Connect to large ground plane for
— — EP EP
maximum thermal dissipation. Do not use as sole ground connection.

Detailed Description A detected transition is flagged through an interrupt pin

(port P31).
The MAX6957 LED driver/GPIO peripheral provides up
to 28 I/O ports, P4 to P31, controlled through an SPI- The Typical Operating Circuit shows two MAX6957s
compatible serial interface. The ports can be config- working together controlling three monocolor 16-seg-
ured to any combination of constant-current LED ment-plus-DP displays, with five ports left available for
drivers, logic inputs and logic outputs, and default to GPIO (P27–P31 of U2).
logic inputs on power-up. When fully configured as an The port configuration registers set the 28 ports, P4 to
LED driver, the MAX6957 controls up to 28 LED seg- P31, individually as either LED drivers or GPIO. A pair
ments with individual 16-step adjustment of the con- of bits in registers 0x09 through 0x0F sets each port’s
stant current through each LED segment. A single configuration (Tables 1 and 2).
resistor sets the maximum segment current for all seg-
The 36-pin MAX6957AAX has 28 ports, P4 to P31. The
ments, with a maximum of 24mA per segment. The
28-pin MAX6957ANI and MAX6957AAI make only 20
MAX6957 drives any combination of discrete LEDs and
ports available. The eight unused ports should be con-
CA digits, including seven-segment and starburst
figured as outputs on power-up by writing 0x55 to reg-
alphanumeric types.
isters 0x09 and 0x0A. If this is not done, the eight
Figure 1 is the MAX6957 functional diagram. Any I/O unused ports remain as floating inputs and quiescent
port can be configured as a push-pull output (sinking supply current rises, although there is no damage to
10mA, sourcing 4.5mA), or a Schmitt-trigger logic the part.
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.

_______________________________________________________________________________________ 5
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
MAX6957

Table 1. Port Configuration Map

ADDRESS REGISTER DATA
REGISTER
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

PORT PORT
REGISTER ADDRESS CONFIGURATION
MODE FUNCTION PIN BEHAVIOR BIT PAIR
(0x20–0x5F) CODE (HEX)
(0xA0–0xDF) UPPER LOWER
Register bit = 0 High impedance

Output LED Segment Driver Open-drain current sink, with sink 0x09 to 0x0F 0 0
Register bit = 1 current (up to 24mA) determined
by the appropriate current register
Active-low logic output
Output GPIO Output Register bit = 0 0x09 to 0x0F 0 1
Active-high logic output
GPIO Input
Input Register bit = Schmitt logic input 0x09 to 0x0F 1 0
Without Pullup
input logic level
Input GPIO Input with Schmitt logic input with pullup 0x09 to 0x0F 1 1
Note: The logic is inverted between the two output modes; a high makes the output go low in LED segment driver mode (0x00) to
turn that segment on; in GPIO output mode (0x01), a high makes the output go high.

Register Control of I/O Ports and LEDs ond driver. The first driver ignores the last 4 bits and
Across Multiple Drivers the second driver ignores the first 4 bits.
The MAX6957 offers 20 or 28 I/O ports, depending on Two addressing methods are available. Any single port
package choice. These can be applied to a variety of (bit) can be written (set/cleared) at once; or, any
combinations of different display types, for example: sequence of eight ports can be written (set/cleared) in
seven, 7-segment digits (Figure 2). This example any combination at once. There are no boundaries; it is
requires two MAX6957s, with one digit being driven by equally acceptable to write P0 through P7, P1 through
both devices, half by one MAX6957, half by the other P8, or P31 through P38 (P32 through P38 are nonexis-
(digit 4 in this example). The two drivers are static, and tent, so the instructions to these bits are ignored).
therefore do not need to be synchronized. The
MAX6957 sees CA digits as multiple discrete LEDs. To Using 8-bit control, a seven-segment digit with a deci-
simplify access to displays that overlap two MAX6957s, mal point can be updated in a single byte-write, a 14-
the MAX6957 provides four virtual ports P0 through P3. segment digit with DP can be updated in two
To update an overlapping digit, send the same code byte-writes, and 16-segment digits with DP can be
twice as an eight-port write, once to P28 through P35 of updated in two byte-writes plus a bit write. Also, dis-
the first driver, and again to P0 through P7 of the sec- crete LEDs and GPIO port bits can be lit and controlled
individually without affecting other ports.

6 _______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander

MAX6957
INTENSITY INTENSITY REGISTERS

TEST TEST REGISTER

CONFIGURATION PORT REGISTERS

P4 TO P31 MASK REGISTER

LED DRIVERS LED DRIVERS AND GPIO
OR GPIO CONFIGURATION
PORT CHANGE
REGISTERS
DETECTOR
DATA CE R/W
8
SEGMENT OR
GPIO DATA R/W

8
COMMAND
REGISTER DECODE

8 8

DATA BYTE COMMAND BYTE

CS D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15

DIN D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15 DOUT

SCLK

Figure 1. MAX6957 Functional Diagram

Shutdown low to clock data into or out of the device, and DIN
When the MAX6957 is in shutdown mode, all ports are must be stable when sampled on the rising edge of
forced to inputs, and the pullup current sources are SCLK. DOUT provides a copy of the bit that was input
turned off. Data in the port and control registers remain 15.5 clocks earlier, or upon a query it outputs internal
unaltered so port configuration and output levels are register data, and is stable on the rising edge of SCLK.
restored when the MAX6957 is taken out of shutdown. Note that the SPI protocol expects DOUT to be high
The display driver can still be programmed while in impedance when the MAX6957 is not being
shutdown mode. For minimum supply current in shut- accessed; DOUT on the MAX6957 is never high
down mode, logic inputs should be at GND or V+ impedance. Go to www.maxim-ic.com/an1879 for
potential. Shutdown mode is exited by setting the S bit ways to convert DOUT to tri-state, if required.
in the configuration register (Table 6). Shutdown mode SCLK and DIN may be used to transmit data to other
is temporarily overridden by the display test function. peripherals, so the MAX6957 ignores all activity on
Serial Interface SCLK and DIN except between the fall and subsequent
The MAX6957 communicates through an SPI-compati- rise of CS.
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

_______________________________________________________________________________________ 7
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
MAX6957

V+
7-SEGMENT DIGIT 1 7-SEGMENT DIGIT 2 7-SEGMENT DIGIT 3 7-SEGMENT DIGIT 4

VIRTUAL SEGMENTS
P0 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 P31

V+
7-SEGMENT DIGIT 5 7-SEGMENT DIGIT 6 7-SEGMENT DIGIT 7

VIRTUAL SEGMENTS
P0 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 P31

Figure 2. Two MAX6957s Controlling Seven 7-Segment Displays

CS

tCSS tCH tCSH

tCSH tCL

SCLK

tDS
tDH

DIN

tDV tDO

DOUT

Figure 3. 4-Wire Interface Timing

8 _______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander

MAX6957
MICROCONTROLLER
SERIAL DATA INPUT

SERIAL CS OUTPUT CS CS CS
MAX6957 MAX6957 MAX6957
SERIAL CLOCK OUTPUT SCLK SCLK SCLK

SERIAL DATA OUTPUT DIN DOUT DIN DOUT DIN DOUT

Figure 4. Daisy-Chain Arrangement for Controlling Multiple MAX6957s

CS

SCLK

DIN D15
D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
=0

DOUT D15 = 0
.

Figure 5. 16-Bit Write Transmission to the MAX6957

Control and Operation Using the Writing Device Registers

The MAX6957 contains a 16-bit shift register into which
4-Wire Interface DIN data are clocked on the rising edge of SCLK, when
Controlling the MAX6957 requires sending a 16-bit CS is low. When CS is high, transitions on SCLK have
word. The first byte, D15 through D8, is the command no effect. When CS goes high, the 16 bits in the Shift
address (Table 3), and the second byte, D7 through register are parallel loaded into a 16-bit latch. The 16
D0, is the data byte (Table 4). bits in the latch are then decoded and executed.
Connecting Multiple MAX6957s to the 4-Wire Bus The MAX6957 is written to using the following
Multiple MAX6957s may be daisy-chained by connect- sequence:
ing the DOUT of one device to the DIN of the next, and 1) Take SCLK low.
driving SCLK and CS lines in parallel (Figure 4). Data at 2) Take CS low. This enables the internal 16-bit shift
DIN propagates through the internal shift registers and register.
appears at DOUT 15.5 clock cycles later, clocked out
on the falling edge of SCLK. When sending commands 3) Clock 16 bits of data into DIN—D15 first, D0 last—
to multiple MAX6957s, all devices are accessed at the observing the setup and hold times (bit D15 is low,
same time. An access requires (16 ✕ n) clock cycles, indicating a write command).
where n is the number of MAX6957s connected togeth- 4) Take CS high (either while SCLK is still high after
er. To update just one device in a daisy-chain, the user clocking in the last data bit, or after taking SCLK
can send the No-Op command (0x00) to the others. low).
5) Take SCLK low (if not already low).
Figure 5 shows a write operation when 16 bits are
transmitted.

_______________________________________________________________________________________ 9
 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 active-high interrupt output (INT). Note that the
MAX6957

MAX6957 between taking CS low and taking CS high MAX6957 does not identify which specific port(s)
again. In this case, only the last 16 bits clocked into the caused the interrupt, but provides an alert that one or
MAX6957 are retained. more port levels have changed.
Reading Device Registers The mask register contains 7 mask bits that select
Any register data within the MAX6957 may be read by which of the seven ports P24–P30 are to be monitored
sending a logic high to bit D15. The sequence is: (Table 13). Set the appropriate mask bit to enable that
port for transition detect. Clear the mask bit if transitions
1) Take SCLK low. on that port are to be ignored. Transition detection
2) Take CS low (this enables the internal 16-bit shift works regardless of whether the port being monitored is
register). set to input or output, but generally it is not particularly
3) Clock 16 bits of data into DIN—D15 first to D0 last. useful to enable transition detection for outputs.
D15 is high, indicating a read command and bits Port P31 must be configured as an output in order to
D14 through D8 containing the address of the regis- work as the interrupt output INT when transition detec-
ter to be read. Bits D7–D0 contain dummy data, tion is used. Port P31 is set as output by writing bit D7
which is discarded. = 0 and bit D6 = 1 to the port configuration register
4) Take CS high (either while SCLK is still high after (Table 1).
clocking in the last data bit, or after taking SCLK To use transition detection, first set up the mask regis-
low), positions D7 through D0 in the Shift register ter and configure port P31 as an output, as described
are now loaded with the register data addressed by above. Then enable transition detection by setting the
bits D1 through D8. M bit in the configuration register (Table 8). Whenever
5) Take SCLK low (if not already low). the configuration register is written with the M bit set,
the MAX6957 updates an internal 7-bit snapshot regis-
6) Issue another read or write command (which can ter, which holds the comparison copy of the logic states
be a No-Op), and examine the bit stream at DOUT; of ports P24 through P30. The update action occurs
the second 8 bits are the contents of the register regardless of the previous state of the M bit, so that it is
addressed by bits D1 through D8 in step 3. not necessary to clear the M bit and then set it again to
Initial Power-Up update the snapshot register.
On initial power-up, all control registers are reset, cur- When the configuration register is written with the M bit
rent registers are set to minimum value, and the set, transition detection is enabled and remains
MAX6957 enters shutdown mode (Table 4). enabled until either the configuration register is written
with the M bit clear, or a transition is detected. The INT
LED Current Control output port P31 goes low, if it was not already low.
LED segment drive current can be set either globally or Once transition detection is enabled, the MAX6957
individually. Global control simplifies the operation continuously compares the snapshot register against
when all LEDs are set to the same current level, the changing states of P24 through P31. If a change on
because writing one register, the Global Current regis- any of the monitored ports is detected, even for a short
ter, sets the current for all ports configured as LED seg- time (like a pulse), INT output port P31 is latched high.
ment drivers. It is also possible to individually control The INT output is not cleared if more changes occur or
the current drive of each LED segment driver. if the data pattern returns to its original snapshot condi-
Individual/global brightness control is selected by set- tion. The only way to clear INT is to access (read or
ting the configuration register I bit (Table7). The global write) the transition detection mask register (Table 13).
current register (0x02) data are then ignored, and seg-
Transition detection is a one-shot event. When INT has
ment currents are set using register addresses 0x12
been cleared after responding to a transition event,
through 0x1F (Tables 10, 11, and 12). Each segment is
transition detection is automatically disabled, even
controlled by a nibble of one of the 16 current registers.
though the M bit in the configuration register remains
Transition (Port Data Change) Detection set (unless cleared by the user). Reenable transition
Port transition detection allows any combination of the detection by writing the configuration register with the
seven ports P24–P30 to be continuously monitored for M bit set to take a new snapshot of the seven ports,
changes in their logic status (Figure 6). A detected P24 to P30.
change is flagged on port P31, which is used as an

10 ______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander

MAX6957
Table 3. Register Address Map
COMMAND ADDRESS HEX
REGISTER
D15 D14 D13 D12 D11 D10 D9 D8 CODE
No-Op R/ W 0 0 0 0 0 0 0 0x00
Global Current R/ W 0 0 0 0 0 1 0 0x02
Configuration R/ W 0 0 0 0 1 0 0 0x04
Transition Detect Mask R/ W 0 0 0 0 1 1 0 0x06
Display Test R/ W 0 0 0 0 1 1 1 0x07
Port Configuration P7, P6, P5, P4 R/ W 0 0 0 1 0 0 1 0x09
Port Configuration P11, P10, P9, P8 R/ W 0 0 0 1 0 1 0 0x0A
Port Configuration P15, P14, P13, P12 R/ W 0 0 0 1 0 1 1 0x0B
Port Configuration P19, P18, P17, P16 R/ W 0 0 0 1 1 0 0 0x0C
Port Configuration P23, P22, P21, P20 R/ W 0 0 0 1 1 0 1 0x0D
Port Configuration P27, P26, P25, P24 R/ W 0 0 0 1 1 1 0 0x0E
Port Configuration P31, P30, P29, P28 R/ W 0 0 0 1 1 1 1 0x0F
Current054 R/ W 0 0 1 0 0 1 0 0x12
Current076 R/ W 0 0 1 0 0 1 1 0x13
Current098 R/ W 0 0 1 0 1 0 0 0x14
Current0BA R/ W 0 0 1 0 1 0 1 0x15
Current0DC R/ W 0 0 1 0 1 1 0 0x16
Current0FE R/ W 0 0 1 0 1 1 1 0x17
Current110 R/ W 0 0 1 1 0 0 0 0x18
Current132 R/ W 0 0 1 1 0 0 1 0x19
Current154 R/ W 0 0 1 1 0 1 0 0x1A
Current176 R/ W 0 0 1 1 0 1 1 0x1B
Current198 R/ W 0 0 1 1 1 0 0 0x1C
Current1BA R/ W 0 0 1 1 1 0 1 0x1D
Current1DC R/ W 0 0 1 1 1 1 0 0x1E
Current1FE R/ W 0 0 1 1 1 1 1 0x1F
Port 0 only (virtual port, no action) R/ W 0 1 0 0 0 0 0 0x20
Port 1 only (virtual port, no action) R/ W 0 1 0 0 0 0 1 0x21
Port 2 only (virtual port, no action) R/ W 0 1 0 0 0 1 0 0x22
Port 3 only (virtual port, no action) R/ W 0 1 0 0 0 1 1 0x23
Port 4 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 0 1 0 0 0x24
Port 5 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 0 1 0 1 0x25
Port 6 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 0 1 1 0 0x26
Port 7 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 0 1 1 1 0x27
Port 8 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 1 0 0 0 0x28
Port 9 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 1 0 0 1 0x29
Port 10 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 1 0 1 0 0x2A

______________________________________________________________________________________ 11
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
MAX6957

Table 3. Register Address Map (continued)

COMMAND ADDRESS HEX
REGISTER
D15 D14 D13 D12 D11 D10 D9 D8 CODE
Port 11 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 1 0 1 1 0x2B
Port 12 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 1 1 0 0 0x2C
Port 13 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 1 1 0 1 0x2D
Port 14 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 1 1 1 0 0x2E
Port 15 only (data bit D0. D7–D1 read as 0) R/ W 0 1 0 1 1 1 1 0x2F
Port 16 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 0 0 0 0 0x30
Port 17 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 0 0 0 1 0x31
Port 18 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 0 0 1 0 0x32
Port 19 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 0 0 1 1 0x33
Port 20 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 0 1 0 0 0x34
Port 21 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 0 1 0 1 0x35
Port 22 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 0 1 1 0 0x36
Port 23 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 0 1 1 1 0x37
Port 24 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 1 0 0 0 0x38
Port 25 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 1 0 0 1 0x39
Port 26 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 1 0 1 0 0x3A
Port 27 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 1 0 1 1 0x3B
Port 28 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 1 1 0 0 0x3C
Port 29 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 1 1 0 1 0x3D
Port 30 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 1 1 1 0 0x3E
Port 31 only (data bit D0. D7–D1 read as 0) R/ W 0 1 1 1 1 1 1 0x3F
4 ports 4–7 (data bits D0–D3. D4–D7 read as 0)) R/ W 1 0 0 0 0 0 0 0x40
5 ports 4–8 (data bits D0–D4. D5–D7 read as 0) R/ W 1 0 0 0 0 0 1 0x41
6 ports 4–9 (data bits D0–D5. D6–D7 read as 0) R/ W 1 0 0 0 0 1 0 0x42
7 ports 4–10 (data bits D0–D6. D7 reads as 0) R/ W 1 0 0 0 0 1 1 0x43
8 ports 4–11 (data bits D0–D7) R/ W 1 0 0 0 1 0 0 0x44
8 ports 5–12 (data bits D0–D7) R/ W 1 0 0 0 1 0 1 0x45
8 ports 6–13 (data bits D0–D7) R/ W 1 0 0 0 1 1 0 0x46
8 ports 7–14 (data bits D0–D7) R/ W 1 0 0 0 1 1 1 0x47
8 ports 8–15 (data bits D0–D7) R/ W 1 0 0 1 0 0 0 0x48
8 ports 9–16 (data bits D0–D7) R/ W 1 0 0 1 0 0 1 0x49
8 ports 10–17 (data bits D0–D7) R/ W 1 0 0 1 0 1 0 0x4A
8 ports 11–18 (data bits D0–D7) R/ W 1 0 0 1 0 1 1 0x4B
8 ports 12–19 (data bits D0–D7) R/ W 1 0 0 1 1 0 0 0x4C
8 ports 13–20 (data bits D0–D7) R/ W 1 0 0 1 1 0 1 0x4D
8 ports 14–21 (data bits D0–D7) R/ W 1 0 0 1 1 1 0 0x4E
8 ports 15–22 (data bits D0–D7) R/ W 1 0 0 1 1 1 1 0x4F

12 ______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander

MAX6957
Table 3. Register Address Map (continued)
COMMAND ADDRESS HEX
REGISTER
D15 D14 D13 D12 D11 D10 D9 D8 CODE
8 ports 16–23 (data bits D0–D7) R/ W 1 0 1 0 0 0 0 0x50
8 ports 17–24 (data bits D0–D7) R/ W 1 0 1 0 0 0 1 0x51
8 ports 18–25 (data bits D0–D7) R/ W 1 0 1 0 0 1 0 0x52
8 ports 19–26 (data bits D0–D7) R/ W 1 0 1 0 0 1 1 0x53
8 ports 20–27 (data bits D0–D7) R/ W 1 0 1 0 1 0 0 0x54
8 ports 21–28 (data bits D0–D7) R/ W 1 0 1 0 1 0 1 0x55
8 ports 22–29 (data bits D0–D7) R/ W 1 0 1 0 1 1 0 0x56
8 ports 23–30 (data bits D0–D7) R/ W 1 0 1 0 1 1 1 0x57
8 ports 24–31 (data bits D0–D7) R/ W 1 0 1 1 0 0 0 0x58
7 ports 25–31 (data bits D0–D6. D7 reads as 0) R/ W 1 0 1 1 0 0 1 0x59
6 ports 26–31 (data bits D0–D5. D6, D7 read as 0) R/ W 1 0 1 1 0 1 0 0x5A
5 ports 27–31 (data bits D0–D4. D5–D7 read as 0) R/ W 1 0 1 1 0 1 1 0x5B
4 ports 28–31 (data bits D0–D3. D4–D7 read as 0) R/ W 1 0 1 1 1 0 0 0x5C
3 ports 29–31 (data bits D0–D2. D3–D7 read as 0) R/ W 1 0 1 1 1 0 1 0x5D
2 ports 30–31 (data bits D0–D1. D2–D7 read as 0) R/ W 1 0 1 1 1 1 0 0x5E
1 port 31 only (data bit D0. D1–D7 read as 0) R/ W 1 0 1 1 1 1 1 0x5F
Note: Unused bits read as 0.

Display Test Register The recommended value of R ISET is the minimum

allowed value, since it sets the display driver to the
Display test mode turns on all ports configured as LED
maximum allowed segment current. RISET can be a
drivers by overriding, but not altering, all controls and
higher value to set the segment current to a lower maxi-
port registers, except the port configuration register
mum value where desired. The user must also ensure
(Table 14). Only ports configured as LED drivers are
that the maximum current specifications of the LEDs
affected. Ports configured as GPIO push-pull outputs
connected to the driver are not exceeded.
do not change state. In display test mode, each port's
current is temporarily set to 1/2 the maximum current The drive current for each segment can be controlled
limit as controlled by RISET. through programming either the global current register
(Table 9) or individual segment current registers
Selecting External Component RISET (Tables 10, 11, and 12), according to the setting of the
to Set Maximum Segment Current current control bit of the configuration register (Table 7).
The MAX6957 uses an external resistor RISET to set the These registers select the LED’s constant-current drive
maximum segment current. The recommended value, from 16 equal fractions of the maximum segment cur-
39kΩ, sets the maximum current to 24mA, which makes rent. The current difference between successive cur-
the segment current adjustable from 1.5mA to 24mA in rent steps, I STEP , is therefore determined by the
1.5mA steps. formula:
To set a different segment current, use the formula:
ISTEP = ISEG / 16
RISET = 936kΩ / ISEG
If ISEG = 24mA, then ISTEP = 24mA / 16 = 1.5mA.
where ISEG is the desired maximum segment current in mA.

The recommended value of RISET is 39kΩ.

______________________________________________________________________________________ 13
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
MAX6957

GPIO INPUT
GPIO IN
CONDITIONING

GPIO/PORT
OUTPUT LATCH GPIO/PORT OUT

P31

INT R CLOCK PULSE AFTER EACH READ ACCESS TO MASK REGISTER

OUTPUT LATCH S

CONFIGURATION REGISTER M BIT = 1

GPIO IN
GPIO INPUT
D Q
CONDITIONING
P30 GPIO/PORT OUT MASK REGISTER BIT 6
GPIO/PORT OUTPUT LATCH

GPIO INPUT GPIO IN

D Q
CONDITIONING
P29
GPIO/PORT OUT MASK REGISTER BIT 5
GPIO/PORT OUTPUT LATCH

GPIO INPUT GPIO IN

CONDITIONING D Q

P28
GPIO/PORT OUT MASK REGISTER BIT 4
GPIO/PORT OUTPUT LATCH

GPIO INPUT GPIO IN

D Q OR
CONDITIONING
P27
GPIO/PORT OUT MASK REGISTER BIT 3
GPIO/PORT OUTPUT LATCH

GPIO INPUT GPIO IN

D Q
CONDITIONING
P26
GPIO/PORT OUT MASK REGISTER BIT 2
GPIO/PORT OUTPUT LATCH

GPIO INPUT GPIO IN

D Q
CONDITIONING
P25
GPIO/PORT OUT MASK REGISTER BIT 1
GPIO/PORT OUTPUT LATCH

GPIO IN
GPIO INPUT
D Q
CONDITIONING
P24
GPIO/PORT OUT MASK REGISTER LSB
GPIO/PORT OUTPUT LATCH
CLOCK PULSE WHEN WRITING CONFIGURATION REGISTER WITH M BIT SET

Figure 6. Maskable GPIO Ports P24 Through P31

14 ______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Table 4. Power-Up Configuration

MAX6957
ADDRESS REGISTER DATA
REGISTER
POWER-UP CONDITION CODE
FUNCTION
(HEX)
D7 D6 D5 D4 D3 D2 D1 D0
Port Register 0x24 to
LED Off; GPIO Output Low X X X X X X X 0
Bits 4 to 31 0x3F
Global
1/16 (minimum on) 0x02 X X X X 0 0 0 0
Current

Shutdown Enabled
Configuration
Current Control = Global 0x04 0 0 X X X X X 0
Register
Transition Detection Disabled

Input Mask
All Clear (Masked Off) 0x06 X 0 0 0 0 0 0 0
Register
Display Test Normal Operation 0x07 X X X X X X X 0
Port
P7, P6, P5, P4: GPIO Inputs Without Pullup 0x09 1 0 1 0 1 0 1 0
Configuration
Port
P11, P10, P9, P8: GPIO Inputs Without Pullup 0x0A 1 0 1 0 1 0 1 0
Configuration
Port
P15, P14, P13, P12: GPIO Inputs Without Pullup 0x0B 1 0 1 0 1 0 1 0
Configuration
Port
P19, P18, P17, P16: GPIO Inputs Without Pullup 0x0C 1 0 1 0 1 0 1 0
Configuration
Port
P23, P22, P21, P20: GPIO Inputs Without Pullup 0x0D 1 0 1 0 1 0 1 0
Configuration
Port
P27, P26, P25, P24: GPIO Inputs Without Pullup 0x0E 1 0 1 0 1 0 1 0
Configuration
Port
P31, P30, P29, P28: GPIO Inputs Without Pullup 0x0F 1 0 1 0 1 0 1 0
Configuration
Current054 1/16 (minimum on) 0x12 0 0 0 0 0 0 0 0
Current076 1/16 (minimum on) 0x13 0 0 0 0 0 0 0 0
Current098 1/16 (minimum on) 0x14 0 0 0 0 0 0 0 0
Current0BA 1/16 (minimum on) 0x15 0 0 0 0 0 0 0 0
Current0DC 1/16 (minimum on) 0x16 0 0 0 0 0 0 0 0
Current0FE 1/16 (minimum on) 0x17 0 0 0 0 0 0 0 0
Current110 1/16 (minimum on) 0x18 0 0 0 0 0 0 0 0
Current132 1/16 (minimum on) 0x19 0 0 0 0 0 0 0 0
Current154 1/16 (minimum on) 0x1A 0 0 0 0 0 0 0 0
Current176 1/16 (minimum on) 0x1B 0 0 0 0 0 0 0 0
Current198 1/16 (minimum on) 0x1C 0 0 0 0 0 0 0 0
Current1BA 1/16 (minimum on) 0x1D 0 0 0 0 0 0 0 0
Current1DC 1/16 (minimum on) 0x1E 0 0 0 0 0 0 0 0
Current1FE 1/16 (minimum on) 0x1F 0 0 0 0 0 0 0 0
X = unused bits; if read, zero results.

______________________________________________________________________________________ 15
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Table 5. Configuration Register Format
MAX6957

ADDRESS CODE REGISTER DATA

FUNCTION
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Configuration Register 0x04 M I X X X X X S
X = Don’t care bit.

Table 6. Shutdown Control (S Data Bit D0) Format

ADDRESS CODE REGISTER DATA
FUNCTION
(HEX) 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
X = Don’t care bit.

Table 7. Global Current Control (I Data Bit D6) Format

ADDRESS REGISTER DATA
FUNCTION
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
Global
Constant-current limits for all digits are
0x04 M 0 X X X X X S
controlled by one setting in the Global Current
register, 0x02

Individual Segment
Constant-current limit for each digit is
0x04 M 1 X X X X X S
individually controlled by the settings in the
Current054 through Current1FE registers
X = Don’t care bit.

Table 8. Transition Detection Control (M-Data Bit D7) Format

ADDRESS CODE REGISTER DATA
FUNCTION
(HEX) 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
X = Don’t care bit.

Table 9. Global Segment Current Register Format

LED DRIVE TYPICAL SEGMENT ADDRESS
D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
FRACTION CURRENT (mA) CODE (HEX)
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.

16 ______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander

MAX6957
Table 9. Global Segment Current Register Format (continued)
LED DRIVE TYPICAL SEGMENT ADDRESS
D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
FRACTION CURRENT (mA) CODE (HEX)
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 ADDRESS
D7 D6 D5 D4 D3 D2 D1 D0
FUNCTION CODE (HEX)
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

______________________________________________________________________________________ 17
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
MAX6957

Table 11. Even Individual Segment Current Format

SEGMENT
LED DRIVE CONSTANT ADDRESS
D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
FRACTION CURRENT WITH CODE (HEX)
RISET = 39kΩ (mA)

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

Applications Information of the 36-pin SSOP package with an ambient tempera-

ture up to +98°C. If a higher supply voltage is used or
Driving Bicolor and Tricolor LEDs the LEDs used have a lower forward-voltage drop than
Bicolor digits group a red and a green die together for 2.4V, the MAX6957 absorbs a higher voltage, and the
each display element, so that the element can be lit MAX6957's power dissipation increases.
red, green (or orange), depending on which die (or If the application requires high drive current and high
both) is lit. The MAX6957 allows each segment's cur- supply voltage, consider adding a series resistor to
rent to be set individually from 1/16th (minimum current each LED to drop excessive drive voltage off-chip. For
and LED intensity) to 16/16th (maximum current and example, consider the requirement that the MAX6957
LED intensity), as well as off (zero current). Thus, a must drive LEDs with a 2.0V to 2.4V specified forward-
bicolor (red-green) segment pair can be set to 289 voltage drop, from an input supply range is 5V ±5%
color/intensity combinations. A discrete or CA tricolor with a maximum LED current of 20mA. Minimum input
(red-green-yellow or red-green-blue) segment triad can supply voltage is 4.75V. Maximum LED series resistor
be set to 4913 color/intensity combinations. value is (4.75V - 2.4V - 0.6V)/0.020A = 87.5Ω. We
Power Dissipation Issues choose 82Ω ±2%. Worst-case resistor dissipation is at
Each MAX6957 port can sink a current of 24mA into an maximum toleranced resistance, i.e., (0.020A)2 ✕ (82Ω
LED with a 2.4V forward-voltage drop when operated ✕ 1.02) = 34mW. The maximum MAX6957 dissipation
from a supply voltage of at least 3.0V. The minimum per LED is at maximum input supply voltage, minimum
voltage drop across the internal LED drivers is therefore toleranced resistance, minimum toleranced LED for-
(3.0V - 2.4V) = 0.6V. The MAX6957 can sink 28 x 24mA ward-voltage drop, i.e., 0.020 x (5.25V - 2.0V - (0.020A
= 672mA when all outputs are operating as LED seg- ✕ 82Ω x 0.98)) = 32.86mW. Worst-case MAX6957 dissi-
ment drivers at full current. On a 3.3V supply, a pation is 920mW, driving all 28 LEDs at 20mA full cur-
MAX6957 dissipates (3.3V - 2.4V) ✕ 672mA = 0.6W rent at once, which meets the 941mW dissipation
when driving 28 of these 2.4V forward-voltage drop ratings of the 36-pin SSOP package.
LEDs at full current. This dissipation is within the ratings

18 ______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Low-Voltage Operation up initially to at least 2.5V to trigger the device's internal

MAX6957
The MAX6957 operates down to 2V supply voltage reset, and also that the serial interface is constrained to
(although the sourcing and sinking currents are not 10Mbps.
guaranteed), providing that the MAX6957 is powered

Table 12. Odd Individual Segment Current Format

SEGMENT
LED
CONSTANT ADDRESS
DRIVE D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE
CURRENT WITH CODE (HEX)
FRACTION
RISET = 39kΩ (mA)
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

REGISTER REGISTER DATA
READ/
FUNCTION ADDRESS
WRITE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0

Read 0 Port Port Port Port Port Port Port

Mask
0x06 30 29 28 27 26 25 24
Register
Write Unchanged mask mask mask mask mask mask mask

X = Don’t care bit.

ADDRESS CODE REGISTER DATA

MODE
(HEX) 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

______________________________________________________________________________________ 19
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
MAX6957

SPI Routing Considerations useful to reduce supply impedance if the MAX6957

The MAX6957’s SPI interface is guaranteed to operate at outputs are to be heavily loaded. Keep the track length
26Mbps on a 2.5V supply, and on a 5V supply typically from the ISET pin to the RISET resistor as short as pos-
operates at 50Mbps. This means that the transmission sible, and take the GND end of the resistor either to the
line issues should be considered when the interface con- ground plane or directly to the GND pins.
nections are longer that 100mm, particularly with higher Power-Supply Considerations
supply voltages. Ringing manifests itself as communica-
tion issues, often intermittent, typically due to double The MAX6957 operates with power-supply voltages of
clocking due to ringing at the SCLK input. Fit a 1kΩ to 2.5V to 5.5V. Bypass the power supply to GND with a
10kΩ parallel termination resistor to either GND or V+ at 0.047µF capacitor as close to the device as possible.
the DIN, SCLK, and CS input to damp ringing for moder- Add a 1µF capacitor if the MAX6957 is far away from
ately long interface runs. Use line impedance matching the board's input bulk decoupling capacitor.
terminations when making connections between boards. Chip Information
PC Board Layout Considerations TRANSISTOR COUNT: 30,316
Ensure that all the MAX6957 GND connections are PROCESS: CMOS
used. A ground plane is not necessary, but may be

Pin Configurations (continued)

TOP VIEW
DOUT

SCLK
GND
GND
GND
ISET

N.C.
DIN
CS
V+
40
39
38
37
36
35
34
33
32
31
ISET 1 36 V+

GND 2 35 CS P8 1 30 P4
P12 2 29 P31
GND 3 34 DIN
P9 3 28 P5
DOUT 4 33 SCLK P13 4 27 P30
P8 5 32 P4 P10 5 26 P6
P14 6 25 P29
P12 6 31 P31 MAX6957
P11 7 24 P7
P9 7 30 P5 P15 8 23 P28
P13 8 29 P30 P16 9 22 P27
MAX6957 P17 10 21 P26
P10 9 28 P6
11
12
13
14
15
16
17
18
19
20

P14 10 27 P29

P11 11 26 P7
P24
N.C.
P18
P19
P20
P21
P22
P23

P25
N.C.

P15 12 25 P28
TQFN
P16 13 24 P27

P17 14 23 P26

P18 15 22 P25

P19 16 21 P24

P20 17 20 P23

P21 18 19 P22

SSOP

20 ______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander

MAX6957
Typical Operating Circuit

3V
3V
36 V+ P4 32 a1 LED1
47nF P5 30 a2
3 GND P6 28 b
2 GND P7 26 c
1 ISET P8 5 d1
39kΩ P9 7 d2
P10 9 e
4-WIRE DATA IN
34 DIN P11 11 f
4-WIRE CLOCK IN
33 SCLK U1 P12 6 g1
35 CS P13 8 g2
CHIP SELECT
MAX6957AAX
4 DOUT P14 10 h
P15 12 i
31 P31 P16 13 j
29 P30 P17 14 k
27 P29 P18 15 l
25 P28 P19 16 m
24 P27 P20 17 dp
23 P26 P21 18 ca
22 P25 P22 19
21 P24 P23 20
a1 LED2
a2
b
c
d1
d2
e
f
g1
g2
h
i
j
3V
k
36 V+ 32
P4 l
30
47nF P5 m
3 GND 28
P6 dp
2 GND 26
P7 ca
1 ISET 5
P8
39kΩ 7
P9
P10 9 a1 LED3
34 DIN
U2 P11 11 a2
33 SCLK P12 6 b
35 CS P13 8 c
MAX6957AAX
4-WIRE DATA OUT
4 DOUT P14 10 d1
P15 12 d2
IRQ OUT
31 P31 P16 13 e
29 P30 P17 14 f
27 P29 P18 15 g1
25 P28 P19 16 g2
24 P27 P20 17 h
23 P26 P21 18 i
1 2 22 P25 P22 19 j
21
P24 P23 20 k
l
SW1 SW2 SW3 m
dp
ca

______________________________________________________________________________________ 21
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Package Information
MAX6957

(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.)

SSOP.EPS
2 1

INCHES MILLIMETERS
DIM MIN MAX MIN MAX INCHES MILLIMETERS
A 0.068 0.078 1.73 1.99 MIN MAX MIN MAX N
A1 0.002 0.008 0.05 0.21 D 0.239 0.249 6.07 6.33 14L
B 0.010 0.015 0.25 0.38 D 0.239 0.249 6.07 6.33 16L
C 0.004 0.008 0.09 0.20 D 0.278 0.289 7.07 7.33 20L
E H D SEE VARIATIONS D 0.317 0.328 8.07 8.33 24L
D 0.397 0.407 10.07 10.33 28L
E 0.205 0.212 5.20 5.38
e 0.0256 BSC 0.65 BSC
H 0.301 0.311 7.65 7.90
L 0.025 0.037 0.63 0.95
0∞ 8∞ 0∞ 8∞

C
B
e A1 L

NOTES:
1. D&E DO NOT INCLUDE MOLD FLASH.
2. MOLD FLASH OR PROTRUSIONS NOT TO EXCEED .15 MM (.006").
PROPRIETARY INFORMATION
3. CONTROLLING DIMENSION: MILLIMETERS. TITLE:

4. MEETS JEDEC MO150. PACKAGE OUTLINE, SSOP, 5.3 MM

5. LEADS TO BE COPLANAR WITHIN 0.10 MM. APPROVAL DOCUMENT CONTROL NO. REV.
1
21-0056 C 1

22 ______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Package Information (continued)

MAX6957
(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.)

SSOP.EPS
36
INCHES MILLIMETERS
DIM MIN MAX MIN MAX
A 0.096 0.104 2.44 2.65
A1 0.004 0.011 0.10 0.29
B 0.012 0.017 0.30 0.44
C 0.009 0.013 0.23 0.32
E H e 0.0315 BSC 0.80 BSC
E 0.291 0.299 7.40 7.60
H 0.398 0.414 10.11 10.51
L 0.020 0.040 0.51 1.02
D 0.598 0.612 15.20 15.55

1
TOP VIEW

A1 A C

e 0∞-8∞
B L

FRONT VIEW SIDE VIEW

PROPRIETARY INFORMATION
TITLE:

PACKAGE OUTLINE, 36L SSOP, 0.80 MM PITCH

APPROVAL DOCUMENT CONTROL NO. REV.
1
21-0040 E 1

______________________________________________________________________________________ 23
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
MAX6957

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.)

QFN THIN.EPS

24 ______________________________________________________________________________________
 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Package Information (continued)

MAX6957
(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

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.