MAX7324
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 MAX7324 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
+5V supply:
R
LED
= (5 - 2.2 - 0.1) / 0.01 = 270Ω
Driving Load Currents Higher than 20mA
The MAX7324 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 four paralleled outputs. Any combi-
nation 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 MAX7324. Do
not exceed a total sink current of 100mA for the device.
Protect the MAX7324 from the negative voltage tran-
sient 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 MAX7324 operates with a supply voltage of
+1.71V to +5.5V over the -40°C to +125°C tempera-
ture 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.
I
2
C Port Expander with Eight Push-Pull Outputs
and Eight Inputs
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