Pin Configurations are continued at end of data sheet.
Typical Application Circuit and Functional Diagram appear
at end of data sheet.
●Cell Phones
●SAN/NAS
●Servers
●Notebooks
●Satellite Radio
General Description
The MAX7321 2-wire serial-interfaced peripheral features
eight open-drain I/O ports with selectable internal pullups
and transition detection. Any port may be used as a logic
input or an open-drain output. Ports are overvoltage
protected to +6V independent of supply voltage.
All I/O ports configured as inputs are continuously
monitored for state changes (transition detection). State
changes are indicated by the open-drain INT output.
The interrupt is latched, allowing detection of transient
changes. When the MAX7321 is subsequently accessed
through the serial interface, any pending interrupt is
cleared.
The open-drain outputs are rated to sink 20mA and are
capable of driving LEDs.
The RST input clears the serial interface, terminating any
I2C communication to or from the MAX7321.
The MAX7321 uses two address inputs with four-level
logic to allow 16 I2C slave addresses. The slave address
also determines the power-up logic state for the I/O ports,
and enables or disables internal 40kΩ pullups in groups
of four ports.
The MAX7321 is one device in a family of pin-compatible
port expanders with a choice of input ports, open-drain
I/O ports, and push-pull output ports (see Table 1).
The MAX7321 is available in 16-pin QSOP and TQFN
packages, and is specified over the automotive temper-
ature range (-40°C to +125°C).
Features
●400kHz I2C Serial Interface
●+1.71V to +5.5V Operating Voltage
●8 Open-Drain I/O Ports Rated to 20mA Sink Current
●I/O Ports Are Overvoltage Protected to +6V
●Any Port Can Be a Logic Input or an Open-Drain
Output
●Selectable I/O Port Power-Up Default Logic States
●Transient Changes Are Latched, Allowing Detection
Between Read Operations
●INT Output Alerts Change on Inputs
●AD0 and AD2 Inputs Select from 16 Slave
Addresses
●Low 0.6µA (typ) Standby Current
●-40°C to +125°C Operating Temperature
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
PART INPUTS INTERRUPT
MASK
OPEN-
DRAIN
OUTPUTS
PUSH-PULL
OUTPUTS
MAX7319 8 Yes — —
MAX7320 — — — 8
MAX7321 Up to 8 — Up to 8 —
MAX7322 4 Yes — 4
MAX7323 Up to 4 — Up to 4 4
MAX7328 Up to 8 — Up to 8 —
MAX7329 Up to 8 — Up to 8 —
PART TEMP RANGE PIN-
PACKAGE
TOP
MARK
MAX7321AEE+ -40°C to +125°C 16 QSOP —
MAX7321ATE+ -40°C to +125°C 16 TQFN-EP* ADC
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
AD0 V+
SDA
SCL
INT
P7
P6
P5
P4
MAX7321
QSOP
RST
AD2
P2
P0
P1
P3
GND
+
MAX7321 I2C Port Expander with 8 Open-Drain I/Os
19-3738; Rev 4; 7/14
Selector Guide
Ordering Information
Pin Congurations
Applications
(All voltages referenced to GND.)
Supply Voltage V+ ...................................................-0.3V to +6V
SCL, SDA, AD0, AD2, RST, INT, P0–P7 ...............-0.3V to +6V
P0–P7 Sink Current ....................................................... 25mA
SDA Sink Current .............................................................. 10mA
INT Sink Current.................................................................10mA
Total V+ Current .................................................................50mA
Total GND Current ...........................................................100mA
Continuous Power Dissipation (TA = +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)..........667mW
16-Pin TQFN (derate 15.6mW/°C above +70°C) ......1250mW
Operating Temperature Range ......................... -40°C to +125°C
Junction Temperature ...................................................... +150°C
Storage Temperature Range ............................ -65°C to +150°C
Lead Temperature (soldering, 10s) ................................. +300°C
Soldering Temperature (reflow)
QSOP ..........................................................................+240°C
TQFN ........................................................................... +260°C
(V+ = +1.71V to +5.5V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at V+ = +3.3V, TA = +25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Operating Supply Voltage V+1.71 5.50 V
Power-On Reset Voltage VPOR V+ falling 1.6 V
Standby Current
(Interface Idle) ISTB SCL and SDA and other digital inputs at V+ 0.6 1.5 µA
Supply Current
(Interface Running) I+fSCL = 400kHz; other digital inputs at V+ 23 55 µA
Input High Voltage
SDA, SCL, AD0, AD2, RST, P0–P7 VIH
V+ < 1.8V 0.8 x V+ V
V+ ≥ 1.8 0.7 x V+
Input Low Voltage
SDA, SCL, AD0, AD2, RST, P0–P7 VIL
V+ < 1.8V 0.2 x V+ V
V+ ≥ 1.8V 0.3 x V+
Input Leakage Current
SDA, SCL, AD0, AD2, RST, P0–P7 IIH, IIL
SDA, SCL, AD0, AD2, RST, P0–P7 at V+ or
GND, internal pullup disabled -0.2 +0.2 µA
Input Capacitance
SDA, SCL, AD0, AD2, RST, P0–P7 10 pF
Output Low Voltage P0–P7 VOL
V+ = +1.71V, ISINK = 5mA 90 180
mV
V+ = +2.5V, ISINK = 10mA 110 210
V+ = +3.3V, ISINK = 15mA 130 230
V+ = +5V, ISINK = 20mA 140 250
Output Low Voltage SDA VOLSDA ISINK = 6mA 250 mV
Output Low Voltage INT VOLINT ISINK = 5mA 130 250 mV
Port Input Pullup Resistor RPU 25 40 55 kΩ
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MAX7321 I2C Port Expander with 8 Open-Drain I/Os
Electrical Characteristics
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Absolute Maximum Ratings
Note 1: All parameters tested at TA = +25°C. Specifications over temperature are guaranteed by design.
Note 2: A master device must provide a hold time of at least 300ns for the SDA signal (referred to VIL of the SCL signal) in order to
bridge the undefined region of SCL’s falling edge.
Note 3: Guaranteed by design.
Note 4: Cb = total capacitance of one bus line in pF. ISINK ≤ 6mA. tR and tF measured between 0.3 x V+ and 0.7 x V+.
Note 5: Input filters on the SDA and SCL inputs suppress noise spikes less than 50ns.
(V+ = +1.71V to +5.5V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at V+ = +3.3V, TA = +25°C.) (Note 1)
(V+ = +1.71V to +5.5V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at V+ = +3.3V, TA = +25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Port Output Data Valid tPPV CL ≤ 100pF 4 µs
Port Input Setup Time tPSU CL ≤ 100pF 0 µs
Port Input Hold Time tPH CL ≤ 100pF 4 µs
INT Input Data Valid Time tIV CL ≤ 100pF 4 µs
INT Reset Delay Time from STOP tIP CL ≤ 100pF 4 µs
INT Reset Delay Time from
Acknowledge tIR CL ≤ 100pF 4 µs
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Serial-Clock Frequency fSCL 400 kHz
Bus Free Time Between a STOP
and a START Condition tBUF 1.3 µs
Hold Time (Repeated) START
Condition tHD, STA 0.6 µs
Repeated START Condition Setup
Time tSU, STA 0.6 µs
STOP Condition Setup Time tSU, STO 0.6 µs
Data Hold Time tHD, DAT (Note 2) 0.9 µs
Data Setup Time tSU, DAT 100 ns
SCL Clock Low Period tLOW 1.3 µs
SCL Clock High Period tHIGH 0.7 µs
Rise Time of Both SDA and SCL
Signals, Receiving tR(Notes 3, 4) 20 +
0.1Cb
300 ns
Fall Time of Both SDA and SCL
Signals, Receiving tF(Notes 3, 4) 20 +
0.1Cb
300 ns
Fall Time of SDA, Transmitting tF,TX (Notes 3, 4) 20 +
0.1Cb
250 ns
Pulse Width of Spike Suppressed tSP (Note 5) 50 ns
Capacitive Load for Each Bus
Line Cb(Note 3) 400 pF
RST Pulse Width tW500 ns
RST Rising to START Condition
Setup Time tRST 1 µs
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MAX7321 I2C Port Expander with 8 Open-Drain I/Os
Timing Characteristics
Port and Interrupt INT Timing Characteristics
(TA = +25°C, unless otherwise noted.)
PIN NAME FUNCTION
QSOP TQFN
1, 3 15, 1 AD0,
AD2
Address Inputs. Select device slave address with AD0 and AD2. Connect AD0 and
AD2 to either GND, V+, SCL, or SDA to give four logic combinations (see Table 3).
2 16 RST Reset Input, Active Low. Drive RST low to clear the 2-wire interface.
4–7, 9–12 2–5, 7–10 P0–P7 Input/output Ports. P0 to P7 are open-drain I/Os.
8 6 GND Ground
13 11 INT Interrupt Output. INT is an open-drain output.
14 12 SCL I2C-Compatible Serial-Clock Input
15 13 SDA I2C-Compatible Serial-Data I/O
16 14 V+ Positive Supply Voltage. Bypass V+ to GND with a ceramic capacitor of at least
0.047µF as close to the device as possible.
— EP EP Exposed Pad. Connect exposed pad to GND.
OUTPUT VOLTAGE LOW
vs. TEMPERATURE
TEMPERATURE (°C)
OUTPUT VOLTAGE LOW (V)
MAX7321 toc03
-40 -25 -10 5 20 35 50 65 80 95 110 125
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
V+ = +5.0V
ISINK = 20mA
V+ = +2.5V
ISINK = 10mA
V+ = +1.71V
ISINK = 5mA
V+ = +3.3V
ISINK = 15mA
0
20
10
40
30
50
60
-40 -10 5 20-25 35 50 65 80 95 110 125
SUPPLY CURRENT vs. TEMPERATURE
MAX7321 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
V+ = +3.3V
V+ = +5.0V
V+ = +1.71V
V+ = +2.5V
fSCL = 400kHz
0
0.4
0.2
1.0
0.8
0.6
1.2
1.4
1.8
1.6
2.0
-40 -10 5-25 20 35 50 65 80 95 110 125
STANDBY CURRENT vs. TEMPERATURE
MAX7321 toc01
TEMPERATURE (°C)
STANDBY CURRENT (µA)
V+ = +3.3V
V+ = +2.5V
V+ = +5.0V
V+ = +1.71V
fSCL = 0kHz
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MAX7321 I2C Port Expander with 8 Open-Drain I/Os
Pin Description
Typical Operating Characteristics
Detailed Description
MAX7319–MAX7329 Family Comparison
The MAX7319–MAX7323 family consists of five pin-
compatible, eight-port expanders. Each version is optimized
for different applications. The MAX7328 and MAX7329
are industry standard parts.
The MAX7324–MAX7327 family consists of four pin-
compatible, 16-port expanders that integrate the
functions of the MAX7320 and one of either the MAX7319,
MAX7321, MAX7322, or MAX7323.
Functional Overview
The MAX7321 is a general-purpose port expander
operating from a +1.71V to +5.5V supply that provides
eight open-drain I/O ports. Each open-drain output is
rated to sink 20mA, and the entire device is rated to
sink 100mA into all ports combined. The outputs drive
loads connected to supplies up to +5.5V, independent
of the MAX7321’s supply voltage.
The MAX7321 is set to one of 16 I2C slave addresses
(0x60 to 0x6F) using the address select inputs AD0 and
AD2, and is accessed over an I2C serial interface up
to 400kHz. The RST input clears the serial interface in
Table 1. MAX7319–MAX7329 Family Comparison
PART
I2C
SLAVE
ADDRESS
INPUTS
INPUT
INTERRUPT
MASK
OPEN-
DRAIN
OUTPUTS
PUSH-
PULL
OUTPUTS
APPLICATION
8-PORT EXPANDERS
MAX7319 110xxxx 8 Yes — —
Input-only versions:
8 input ports with programmable latching transition
detection interrupt and selectable pullups.
Offers maximum versatility for automatic input
monitoring. An interrupt mask selects which inputs
cause an interrupt on transitions, and transition flags
identify which inputs have changed (even
momentarily) since the ports were last read.
MAX7320 101xxxx — — — 8
Output-only versions:
8 push-pull outputs with selectable power-up default
levels.
Push-pull outputs offer faster rise time than open-
rain outputs, and require no pullup resistors.
MAX7321 110xxxx Up to 8 — Up to 8 —
I/O versions:
8 open-drain I/O ports with latching transition
detection interrupt and selectable pullups.
Open-drain outputs can level shift the logic-high state
to a higher or lower voltage than V+ using external
pullup resistors. Any port can be used as an input by
setting the open-drain output to logic-high. Transition
flags identify which inputs have changed (even
momentarily) since the ports were last read.
MAX7322 110xxxx 4 Yes — 4
4 input-only, 4 output-only versions:
4 input ports with programmable latching transition
detection interrupt and selectable pullups;
4 push-pull outputs with selectable power-up default
levels.
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MAX7321 I2C Port Expander with 8 Open-Drain I/Os
case of a bus lockup, terminating any serial transaction to
or from the MAX7321.
Any port can be configured as a logic input by setting the
port output logic-high (logic-high for an open-drain output
is high impedance). When the MAX7321 is read through
the serial interface, the actual logic levels at the ports are
read back.
The open-drain ports offer latching transition detection
when used as inputs. All input ports are continuously
monitored for changes. An input change sets 1 of 8 flag
bits that identify changed input(s). All flags are cleared
upon a subsequent read or write transaction to the
MAX7321.
A latching interrupt output (INT) is programmed to flag
logic changes on ports used as inputs. Data changes
on any input port forces INT to a logic-low. Changing
the I/O port level through the serial interface does not
cause an interrupt. The interrupt output INT is deassert-
ed when the MAX7321 is next accessed through the
serial interface.
Internal pullup resistors to V+ are selected by the address
select inputs (AD0 and AD2). Pullups are enabled on the
input ports in groups of four (see Table 3).
Use the slave address selection to ensure that I/O ports
used as inputs are logic-high on power-up. I/O ports with
internal pullups enabled default to a logic-high output
state. Ports with internal pullups disabled default to a
logic-low output state. Output port power-up logic states
are selected by the address select inputs AD0 and AD2.
Ports default to logic-high or logic-low on power-up in
groups of four (see Table 3).
Initial Power-Up
On power-up, the transition detection logic is reset, and
INT is deasserted. The transition flags are cleared to
indicate no data changes. The power-up default states
of the eight I/O ports are set according to the I2C slave
address selection inputs, AD0 and AD2 (Table 3). For
I/O ports used as inputs, ensure that the default
states are logic-high so that the I/O ports power up
in the high-impedance state. All I/O ports configured
with pullups enabled also have a logic-high power-up
state.
Power-On Reset
The MAX7321 contains an integral power-on reset
(POR) circuit that ensures all registers are reset to a
known state on power-up. When V+ rises above VPOR
(1.6V max), the POR circuit releases the registers and
2-wire interface for normal operation. When V+ drops to
less than VPOR, the MAX7321 resets all register contents
to the POR defaults (Table 3).
Table 1. MAX7319–MAX7329 Family Comparison (continued)
PART
I2C
SLAVE
ADDRESS
INPUTS
INPUT
INTERRUPT
MASK
OPEN-
DRAIN
OUTPUTS
PUSH-
PULL
OUTPUTS
APPLICATION
MAX7323 110xxxx Up to 4 — Up to 4 4
4 I/O, 4 output-only versions:
4 open-drain I/O ports with latching transition
detection interrupt and selectable pullups.
4 push-pull outputs with selectable power-up default
levels.
MAX7328
MAX7329
0100xxx
0111xxx Up to 8 — Up to 8 —
8 open-drain I/O ports with nonlatching transition
detection interrupt and pullups on all ports.
All ports power up as inputs (or logic-high outputs).
Any port can be used as an input by setting the open-
drain output to logic-high.
16-PORT EXPANDERS
MAX7324
101xxxx
And
110xxxx
8 Yes — 8 Software equivalent to a MAX7320 plus a MAX7319.
MAX7325 Up to 8 — Up to 8 8 Software equivalent to a MAX7320 plus a MAX7321.
MAX7326 4 Yes — 12 Software equivalent to a MAX7320 plus a MAX7322.
MAX7327 Up to 4 — Up to 4 12 Software equivalent to a MAX7320 plus a MAX7323.
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MAX7321 I2C Port Expander with 8 Open-Drain I/Os
RST Input
The RST input voids any I2C transaction involving the
MAX7321, forcing the MAX7321 into the I2C STOP
condition. A reset does not affect the INT interrupt output.
Standby Mode
When the serial interface is idle, the MAX7321 automat-
ically enters standby mode, drawing minimal supply
current.
Slave Address, Power-Up Default Logic
Levels, and Input Pullup Selection
Address inputs AD0 and AD2 determine the MAX7321
slave address, set the power-up I/O state for the ports,
and select which inputs have pullup resistors. Internal
pullups and power-up default states are set in groups
of four (Table 3). The MAX7319, MAX7321, MAX7322,
and MAX7323 use a different range of slave addresses
(110xxxx) than the MAX7320 (101xxxx) (Table 2).
The MAX7321 slave address is determined on each I2C
transmission, regardless of whether the transmission
is actually addressing the MAX7321. The MAX7321
distinguishes whether address inputs AD2 and AD0 are
connected to SDA or SCL instead of fixed logic levels
V+ or GND during this transmission. This means that the
MAX7321 slave address can be configured dynamically in
the application without cycling the device supply.
On initial power-up, the MAX7321 cannot decode
address inputs AD0 and AD2 fully until the first I2C
transmission. AD0 and AD2 initially appear to be
connected to V+ or GND. This is important because the
address selection is used to determine the power-up
logic state and whether pullups are enabled. However,
at power-up, the I2C SDA and SCL bus interface lines
are high impedance at the pins of every device (master
or slave) connected to the bus, including the MAX7321.
This is guaranteed as part of the I2C specification.
Therefore, address inputs AD2 and AD0 that are
connected to SDA or SCL normally appear at power-up to
be connected to V+. The power-up logic uses AD0 to
select the power-up state and whether pullups are
enabled for ports P3–P0, and AD2 for ports P7–P4.
The rule is that a logic-high, SDA, or SCL connection
selects the pullups and sets the default logic state to
high. A logic-low deselects the pullups and sets the
default logic state to low (Table 3). The port configu-
ration is correct on power-up for a standard I2C configu
ration, where SDA or SCL are pulled up to V+ by the
external I2C pullup resistors.
Table 2. Read and Write Access to Eight-Port Expander Family
PART I2C SLAVE
ADDRESS INPUTS INTERRUPT
MASK
OPEN-
DRAIN
OUTPUTS
PUSH-
PULL
OUTPUTS
I2C DATA WRITE I2C DATA READ
MAX7319 110xxxx 8 Yes — — <I7–I0 interrupt
mask>
<I7–I0 port inputs>
<I7–I0 transition flags>
MAX7320 101xxxx — — — 8 <O7–O0 port
outputs> <O7-O0 port inputs>
MAX7321 110xxxx Up to 8 — Up to 8 — <P7–P0 port
outputs>
<P7–P0 port inputs>
<P7–P0 transition flags>
MAX7322 110xxxx 4 Yes — 4
<O7, O6 outputs,
I5–I2 interrupt
mask, O1, O0
outputs>
<O7, O6, I5–I2, O1, O0 port
inputs>
<0, 0, I5–I2 transition flags,
0, 0>
MAX7323 110xxxx Up to 4 — Up to 4 4 <port outputs>
<O7, O6, P5–P2, O1, O0 port
inputs>
<0, 0, P5–P2 transition flags,
0, 0>
MAX7328 0100xxx Up to 8 — Up to 8 — <P7–P0 port
outputs> <P7–P0 port inputs>
MAX7329 0111xxx Up to 8 — Up to 8 — <P7–P0 port
outputs> <P7–P0 port inputs>
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MAX7321 I2C Port Expander with 8 Open-Drain I/Os
There are circumstances where the assumption that SDA
= SCL = V+ on power-up is not true (e.g., in applications
in which there is legitimate bus activity during power-up).
Also, if SDA and SCL are terminated with pullup resis-
tors to a different supply voltage than the MAX7321’s
supply voltage, and if that pullup supply rises later than
the MAX7321’s supply, then SDA or SCL may appear at
power-up to be connected to GND. In such applications,
use the four address combinations that are selected by
connecting address inputs AD2 and AD0 to V+ or GND
(shown in bold in Table 3). These selections are guaran-
teed to be correct at power-up, independent of SDA and
SCL behavior. If one of the other 12 address combinations
is used, an unexpected combination of pullups might be
asserted until the first I2C transmission (to any device,
not necessarily the MAX7321) is put on the bus, and an
unexpected combination of ports may initialize as
logic-low outputs instead of inputs or logic-high outputs.
Port Inputs
I/O port inputs switch at the CMOS-logic levels, as
determined by the expander’s supply voltage, and are
overvoltage tolerant to +6V, independent of the expander’s
supply voltage.
I/O Port Input Transition Detection
All I/O ports configured as inputs are monitored for changes
since the expander was last accessed through the serial
interface. The state of the input ports is stored in an internal
“snapshot” register for transition monitoring. The snapshot
is continuously compared with the actual input conditions,
and if a change is detected for any port, INT is asserted
to signal a state change. An internal transition flag is set
for that port. The input is sampled (internally latched into
the snapshot register) and the old transition flags cleared
during the I2C acknowledge of every MAX7321 read
and write access. The previous port transition flags are
read through the serial interface as the second byte of a
2-byte read sequence.
Table 3. MAX7321 Address Map
PIN CONNECTION DEVICE ADDRESS 40kΩ INPUT PULLUP ENABLES
AD2 AD0 A6 A5 A4 A3 A2 A1 A0 I7 I6 I5 I4 I3 I2 I1 I0
SCL GND 1 1 0 0 0 0 0 Y Y Y Y — — — —
SCL V+ 1 1 0 0 0 0 1 Y Y Y Y Y Y Y Y
SCL SCL 1 1 0 0 0 1 0 Y Y Y Y Y Y Y Y
SCL SDA 1 1 0 0 0 1 1 Y Y Y Y Y Y Y Y
SDA GND 1 1 0 0 1 0 0 Y Y Y Y — — — —
SDA V+ 1 1 0 0 1 0 1 Y Y Y Y Y Y Y Y
SDA SCL 1 1 0 0 1 1 0 Y Y Y Y Y Y Y Y
SDA SDA 1 1 0 0 1 1 1 Y Y Y Y Y Y Y Y
GND GND 1 1 0 1 0 0 0 — — — — — — — —
GND V+ 1 1 0 1 0 0 1 — — — — Y Y Y Y
GND SCL 1 1 0 1 0 1 0 — — — — Y Y Y Y
GND SDA 1 1 0 1 0 1 1 — — — — Y Y Y Y
V+ GND 1 1 0 1 1 0 0 Y Y Y Y — — — —
V+ V+ 1 1 0 1 1 0 1 Y Y Y Y Y Y Y Y
V+ SCL 1 1 0 1 1 1 0 Y Y Y Y Y Y Y Y
V+ SDA 1 1 0 1 1 1 1 Y Y Y Y Y Y Y Y
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MAX7321 I2C Port Expander with 8 Open-Drain I/Os
Serial Interface
Serial Addressing
The MAX7321 operates as a slave that sends and
receives data through an I2C interface. The interface uses
a serial-data line (SDA) and a serial-clock line (SCL) to
achieve bidirectional communication between master(s)
and slave(s). The master initiates all data transfers to
and from the MAX7321 and generates the SCL clock that
synchronizes the data transfer (Figure 1).
SDA operates as both an input and an open-drain output.
A pullup resistor, typically 4.7kΩ, is required on SDA.
SCL operates only as an input. A pullup resistor, typically
4.7kΩ, is required on SCL if there are multiple masters
on the 2-wire interface, or if the master in a single-master
system has an open-drain SCL output.
Each transmission consists of a START condition sent
by a master, followed by the MAX7321’s 7-bit slave address
plus R/W bit, 1 or more data bytes, and finally a STOP
condition (Figure 2).
START and STOP Conditions
Both SCL and SDA remain high when the interface is not
busy. A master signals the beginning of a transmission
with a START (S) condition by transitioning SDA from high
to low while SCL is high. When the master has finished
communicating with the slave, the master issues a STOP
(P) condition by transitioning SDA from low to high while
SCL is high. The bus is then free for another transmission
(Figure 2).
Bit Transfer
One data bit is transferred during each clock pulse.
The data on SDA must remain stable while SCL is high
(Figure 3).
Acknowledge
The acknowledge bit is a clocked 9th bit the recipient uses
to acknowledge receipt of each byte of data (Figure 4).
Each byte transferred effectively requires 9 bits. The
master generates the 9th clock pulse, and the recipient
pulls down SDA during the acknowledge clock pulse,
such that the SDA line is stable low during the high period
of the clock pulse. When the master is transmitting to the
MAX7321, the MAX7321 generates the acknowledge bit
because the device is the recipient. When the MAX7321
is transmitting to the master, the master generates the
acknowledge bit because the master is the recipient.
Slave Address
The MAX7321 has a 7-bit-long slave address (Figure 5).
The eighth bit following the 7-bit slave address is the R/W
bit. It is low for a write command, and high for a read
command.
The first (A6), second (A5), and third (A4) bits of the
MAX7321 slave address are always 1, 1, and 0.
Connect AD2 and AD0 to GND, V+, SDA, or SCL to
select slave address bits A3, A2, A1, and A0. The
MAX7321 has 16 possible slave addresses (Table 3),
allowing up to 16 MAX7321 devices on an I2C bus.
Figure 2. START and STOP Conditions
Figure 1. 2-Wire Serial Interface Timing Details
SDA
SCL
START
CONDITION
STOP
CONDITION
S P
SCL
SDA
tRtF
tBUF
START
CONDITION
STOP
CONDITION
REPEATED START CONDITION
START CONDITION
tSU,STO
tHD,STA
tSU,STA
tHD,DAT
tSU,DAT
tLOW
tHIGH
tHD,STA
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MAX7321 I2C Port Expander with 8 Open-Drain I/Os
Accessing the MAX7321
The MAX7321 is accessed through an I2C interface. The
transition flags are cleared, and INT is deasserted each
time the device acknowledges the I2C slave address.
A single-byte read from the MAX7321 returns the status
of the eight I/O ports.
A 2-byte read returns first the status of the eight I/O ports
(as for a single-byte read), followed by the transition flags.
A multibyte read (more than 2 bytes before the I2C
STOP bit) repeatedly returns the port data, alternating
with the transition flags. As the port data is resampled
for each transmission, and the transition flags are reset
each time, a multibyte read continuously returns the
current data and identifies any changing ports.
If a port data change occurs during the read sequence,
INT is reasserted after the I2C STOP bit. The MAX7321
does not generate another interrupt during a single-byte
or multibyte read.
Port data is sampled during the preceding I2C acknowl-
edge bit (the acknowledge bit for the I2C slave address in
the case of a single-byte or 2-byte read).
A single-byte write to the MAX7321 sets the logic state
of all eight I/O ports.
A multibyte write to the MAX7321 repeatedly sets the
logic state of all eight I/O ports.
Reading from the MAX7321
A read from the MAX7321 starts with the master
transmitting the MAX7321’s slave address with the R/W
bit set high. The MAX7321 acknowledges the slave
address, and samples the ports during the acknowl-
edge bit. INT deasserts during the slave address
acknowledge.
Typically, the master reads 1 or 2 bytes from the
MAX7321, each byte being acknowledged by the master
upon reception with the exception of the last byte.
When the master reads 1 byte from the MAX7321 and
subsequently issues a STOP condition (Figure 6), the
MAX7321 transmits the current port data, clears the
change flags, and resets the transition detection. INT
deasserts during the slave acknowledge. The new
snapshot data is the current port data transmitted to the
master; therefore, port changes ocurring during the
transmission are detected. INT remains high until the
STOP condition.
The master can read 2 bytes from the MAX7321 and
then issue a STOP condition (Figure 7). In this case,
the MAX7321 transmits the current port data, followed
by the change flags. The change flags are then cleared,
and transition detection resets. INT goes high (high
impedance if an external pullup resistor is not fitted) during
the slave acknowledge. The new snapshot data is the
current port data transmitted to the master; therefore, port
changes occurring during the transmission are detected.
INT remains high until the STOP condition.
Figure 4. Acknowledge
Figure 3. Bit Transfer
SCL
SDA BY
TRANSMITTER
CLOCK PULSE
FOR ACKNOWLEDGMENT
START
CONDITION
SDA BY
RECEIVER
1 2 8 9
S
SDA
SCL
DATA LINE STABLE;
DATA VALID
CHANGE OF DATA
ALLOWED
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10
MAX7321 I2C Port Expander with 8 Open-Drain I/Os
Figure 7. Reading the MAX7321 (2 Data Bytes)
Figure 6. Reading the MAX7321 (1 Data Byte)
Figure 5. Slave Address
SCL
MAX7321 SLAVE ADDRESSS 1 1 0 A
P
1
PORTS
INT OUTPUT
R/WPORT SNAPSHOT
tIV
tPH
tIR
AD0D1D2D3D4D5D6D7
PORT SNAPSHOT
tPSU tIP
D7 D6 D5 D4 D3 D2 D1 D0 N
PORT SNAPSHOT
INT REMAINS HIGH UNTIL STOP CONDITION
S = START CONDITION
P = STOP CONDITION
SHADED = SLAVE TRANSMISSION
N = NOT ACKNOWLEDGE
I0
I1
I2I3I4I5
I6
I7 F0
F1
F2F3F4F5
F6
F7
PORT I/O INTERRUPT FLAGS
SCL
MAX7321 SLAVE ADDRESS
S 1 1 0 A P
1
PORT I/O
tIV
N
P0
P1
P2P3P4P5
P6
P7
D0D1D2D3D4D5D6D7
PORT I/O
INT OUTPUT
R/WPORT SNAPSHOT
tPH
tIR
PORT SNAPSHOT
tPSU tIP
INT REMAINS HIGH UNTIL STOP CONDITION
DATA
SDA
SCL
1 1 A3 A2 A1 A0
0R/W
MSB LSB
ACK
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11
MAX7321 I2C Port Expander with 8 Open-Drain I/Os
Writing to the MAX7321
A write to the MAX7321 starts with the master transmit-
ting the MAX7321’s slave address with the R/W bit set
low. The MAX7321 acknowledges the slave address, and
samples the ports (takes a snapshot) during acknowl-
edge. INT goes high (high impedance if an external
pullup resistor is not fitted) during the slave acknowledge.
Typically, the master proceeds to transmit 1 or more bytes
of data. The MAX7321 acknowledges these subsequent
bytes of data and updates the I/O ports with each new
byte until the master issues a STOP condition (Figure 8).
Applications Information
Port Input and I2C Interface Level
Translation from Higher or Lower
Logic Voltages
The MAX7321’s SDA, SCL, AD0, AD2, RST, INT, and
I/O ports P0–P7 are overvoltage protected to +6V inde-
pendent of V+. This allows the MAX7321 to operate from
a lower supply voltage, such as +3.3V, while the I2C
interface and/or any of the eight I/O ports are driven as
inputs driven from a higher logic level, such as +5V.
The MAX7321 can operate from a higher supply volt-
age, such as +3V, while the I2C interface and/or some
of the I/O ports (P0–P7) are driven from a lower logic
level, such as +2.5V. Apply a minimum voltage of
0.7 x V+ to assert a logic-high on any I/O port (e.g.,
a MAX7321 operating from a +5V supply may not
recognize a +3.3V nominal logic-high). One solution for
input-level translation is to drive MAX7321 I/Os from
open-drain outputs. Use a pullup resistor to V+ or a
higher supply to ensure a high logic voltage greater
than 0.7 x V+.
Port-Output Port-Level Translation
The open-drain output architecture allows for level
translation to higher or lower voltages than the
MAX7321’s supply. Use an external pullup resistor on
any output to convert the high-impedance logic-high
condition to a positive voltage level. The resistor can be
connected to any voltage up to +6V, and the resistor
value chosen to ensure no more than 20mA is sunk in
the logic-low condition. For interfacing CMOS inputs, a
pullup resistor value of 220kΩ is a good starting point.
Use a lower resistance to improve noise immunity, in
applications where power consumption is less critical,
or where a faster rise time is needed for a given capac-
itive load.
Each of the I/O ports (P0–P7) has a protection diode to
GND (Figure 9). When a port is driven to a voltage lower
than GND, the protection diode clamps the voltage to a
diode drop below GND.
Each of the P0–P7 I/O ports also has a 40kΩ (typ) pullup
resistor that can be enabled or disabled. When a port
is driven to a voltage higher than V+, the body diode of
the pullup enable switch conducts and the 40kΩ pullup
resistor is enabled. When the MAX7321 is powered
down (V+ = 0), each I/O port appears as a 40kΩ resistor
in series with a diode connected to zero. I/O ports are
protected to +6V under any of these circumstances
(Figure 9).
Figure 8. Writing to the MAX7321
SCL
SDA
START CONDITION R/W
SLAVE ADDRESS
S 0
1 2 3 4 5 6 7 8
A A A
t
PV
DATA 1 DATA 2
t
PV
DATA TO PORT DATA TO PORT
t
PV
DATA 2 VALIDDATA 1 VALID
INTERNAL WRITE
TO PORT
DATA OUT
FROM PORT
t
PV
S = START CONDITION SHADED = SLAVE TRANSMISSION
P = STOP CONDITION N = NOT ACKNOWLEDGE
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12
MAX7321 I2C Port Expander with 8 Open-Drain I/Os
Driving LED Loads
When driving LEDs, a resistor must be fitted in series
with the LED to limit the LED current to no more than
20mA. Connect the LED cathode to the MAX7321 port,
and the LED anode to V+ through the series current-
limiting resistor (RLED). Set the port output low to
illuminate the LED. Choose the resistor value according to
the following formula:
RLED = (VSUPPLY - VLED - VOL)/ILED
where:
RLED is the resistance of the resistor in series with the
LED (Ω).
VSUPPLY is the supply voltage used to drive the LED (V).
VLED is the forward voltage of the LED (V).
VOL is the output-low voltage of the MAX7321 when
sinking ILED (V).
ILED is the desired operating current of the LED (A).
For example, to operate a 2.2V red LED at 10mA from a
+5V supply:
RLED = (5 - 2.2 - 0.07)/0.010 = 270Ω.
Figure 9. MAX7321 I/O Structure
P0–P7
PULLUP
ENABLE
INPUT
OUTPUT
40kΩ
MAX7321
V+ V+
I2C
CONTROL P0
P3
P2
P1
P4
P5
P6
P7
INT
I/O
PORTS
POWER-
ON RESET
INPUT
FILTER
RST
SDA
SCL
AD2
AD0
MAX7321
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13
MAX7321 I2C Port Expander with 8 Open-Drain I/Os
Functional Diagram
Driving Load Currents Higher than 20mA
The MAX7321 can be used to drive loads, such as relays,
that draw more than 20mA by paralleling outputs. Use at
least one output per 20mA of load current; for example,
a 5V, 330mW relay draws 66mA, and therefore, requires
four paralleled outputs. Any combination of outputs can
be used as part of a load-sharing design because any
combination of ports can be set or cleared at the same
time by writing the MAX7321. Do not exceed a total sink
current of 100mA for the device.
The MAX7321 must be protected from the negative
voltage transient generated when switching off inductive
loads (such as relays), by connecting a reverse-biased
diode across the inductive load. Choose the peak cur-
rent for the diode to be greater than the inductive load’s
operating current.
Power-Supply Considerations
The MAX7321 operates with a supply voltage of +1.71V
to +5.5V over the -40°C to +125°C temperature range.
Bypass the supply to GND with a ceramic capacitor of
at least 0.047µF as close as possible to the device. For
the TQFN version, additionally connect the exposed pad
to GND.
Issue: I2C Flag Clearing Deassertion Anomaly
Description of Problem
The MAX7321 clears data stored in the interrupt flag and
deasserts the corresponding interrupt when an I2C mas-
ter reads any I2C slave on the same bus.
Workaround
To keep the interrupt flag data valid, the user must read
the MAX7321 device BEFORE any other device on the
I2C bus, after a pending interrupt. This limits the bus to
only one MAX7321 device.
PACKAGE
TYPE
PACKAGE
CODE OUTLINE NO. LAND
PATTERN NO.
16 QSOP E16+4 21-0055 90-0167
16 TQFN-EP T1633+4 21-0136 90-0031
15
16
14
13
5
6
7
P1
P2
8
AD2
P7
P6
SCL
1 3
V+
4
12 10 9
AD0
RST
P5
P4
GND
P3
MAX7321
P0 INT
2
11
SDA
TQFN
TOP VIEW
*EP
*EXPOSED PAD, CONNECTED TO GND
+
MAX7321
P2
P7
P6
P5
P4
V+
+3.3V +5V
µC
SCL
SDA
SCL
AD0
P1
P0
SDA
P3 I/O
I/O
AD2
GND
I/O
I/O
RST RST
INT INT
0.047µF
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14
MAX7321 I2C Port Expander with 8 Open-Drain I/Os
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
Pin Congurations (continued)
Typical Application Circuit
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 7/05 Initial release —
1 4/06 Updates to data sheet 1–17
2 7/13 Added the I2C Flag Clearing Deassertion Anomaly section 14
3 5/14 No /V OPNs; removed automotive reference from Applications section 1
4 7/14 Revised the Issue: I2C Flag Clearing Deassertion Anomaly section 14
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2014 Maxim Integrated Products, Inc.
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MAX7321 I2C Port Expander with 8 Open-Drain I/Os
Revision History
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
