Port Structures
Each of the four output ports O0, O1, O6, and O7 has
protection diodes to V+ and to GND (Figure 9). When a
port output is driven to a voltage lower than GND, the
appropriate protection diode clamps the output to a
diode drop above V+ or below GND. When the
MAX7322 is powered down (V+ = 0), each output port
appears as a diode clamp to GND (Figure 9).
Each of the four input ports I2–I5 has a protection diode
to GND (Figure 10). When a port input is driven to a
voltage lower than GND, the protection diode will
clamp the input to a diode drop below GND.
Each of the four inputs ports I2–I5 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 MAX7322 is
powered down (V+ = 0), each input port appears as a
40kΩ pullup resistor in series with a diode connected to
zero. Input ports are protected to +6V under any of
these circumstances (Figure 10).
Driving LED Loads
When driving LEDs from one of the four output ports
O0, O1, O6, or O7, a resistor must be connected in
series with the LED to limit the LED current to no more
than 20mA. Connect the LED cathode to the MAX7322
port, and the LED anode to V+ through the series cur-
rent-limiting resistor, R
LED
. Set the port output low to
light the LED. Choose the resistor value according to
the following formula:
R
LED
= (V
SUPPLY
- V
LED
- V
OL
) / I
LED
where:
R
LED
is the resistance of the resistor in series with the
LED (Ω).
V
SUPPLY
is the supply voltage used to drive the
LED (V).
V
LED
is the forward voltage of the LED (V).
V
OL
is the output low voltage of the MAX7322 when
sinking I
LED
(V).
I
LED
is the desired operating current of the LED (A).
For example, to operate a 2.2V red LED at 10mA from a
+5V supply:
R
LED
= (5 - 2.2 - 0.07) / 0.010 = 270Ω
Driving Load Currents Higher than 20mA
The MAX7322 can be used to drive loads, such as
relays, that draw more than 20mA by paralleling out-
puts. Use at least one output per 20mA of load current;
for example, a 5V 330mW relay draws 66mA, and
therefore, requires all four paralleled outputs. Any com-
bination of outputs can be used as part of a load-shar-
ing design, because any combination of ports can be
set or cleared at the same time by writing to the
MAX7322. Do not exceed a total sink current of 100mA
for the device.
The MAX7322 must be protected from the negative
voltage transient generated when switching off induc-
tive 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 induc-
tive load’s operating current.
Power-Supply Considerations
The MAX7322 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.
MAX7322
I
2
C Port Expander with
4 Push-Pull Outputs and 4 Inputs
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