Each of the I/O ports P0–P7 also has a 40k

Ω (typ)

pullup resistor that can be enabled or disabled. When a

the pullup enable switch conducts and the 40k

Ω pullup

resistor is enabled. When the MAX7321 is powered down

(V+ = 0), each I/O port appears as a 40k

Ω resistor in

series with a diode connected to zero. I/O ports are pro-

10).

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-

nate the LED. Choose the resistor value according to

the following formula:

where:

LED (

Ω).

For example, to operate a 2.2V red LED at 10mA from a

+5V supply:

Ω

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 com-

bination of ports can be set or cleared at the same time

by writing the MAX7321. Do not exceed a total sink cur-

rent of 100mA for the device.

The MAX7321 must be protected from the negative volt-

age transient generated when switching off inductive

loads (such as relays), by connecting a reverse-biased

diode across the inductive load. Choose the peak current

for the diode to be greater than the inductive load’s oper-

ating 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 to the device as possible. For the

TQFN version, additionally connect the exposed pad to

GND.

Compatibility with MAX6965, MAX7315, and

MAX7316

The MAX7321 is subset pin compatible with the

MAX6965, MAX7315, and MAX7316. The pin differences

are shown in Table 4. The MAX7321 is not software com-

patible with the MAX6965, MAX7315, or MAX7316. In

many cases, it is possible to design a PC board to work

with all these port expanders, providing design flexibility.

14

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PIN-PACKAGE

PIN FUNCTION

16

QSOP

16

TQFN

MAX7321

MAX7315

MAX6965 AND

MAX7316

115

AD0

AD0

BLINK

216

RST

AD1

RST

31

AD2

AD2

AD0

Table 4. MAX7321, MAX6965, MAX7315,

and MAX7316 Pin Compatibility

MAX7321

P2

P7

P6

P5

P4

V+

+3.3V

+5V

µC

SCL

SDA

SCL

AD0

P1

P0

SDA

P3

GND

I/O

I/O

AD2

I/O

I/O

RST

RST

INT

INT

0.047

µF

Typical Application Circuit