Datasheet

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 pul-
lup 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 current-
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
outputs. 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
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 to the
MAX7322. Do not exceed a total sink current of 100mA
for the device.
The MAX7322 must be protected from the nega-
tive voltage 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 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 0.047°F as close to the device as
possible. For the TQFN version, additionally connect the
exposed pad to GND.
Figure 10. MAX7322 Input Port Structure
Figure 9. MAX7322 Push-Pull Output Port Structure
PORTS
I2–I5
PULLUP
ENABLE
INPUT
40kΩ
MAX7322
V+
V+
OUTPUT
V+V+
PORTS
O0, O1, O6, O7
MAX7322
www.maximintegrated.com
Maxim Integrated │ 14
MAX7322 I
2
C Port Expander with
4 Push-Pull Outputs and 4 Inputs