MAX7324 Maxim, MAX7324 Datasheet - Page 16

• Manufacturer Part Number: MAX7324
• Description: The MAX7324 2-wire serial-interfaced peripheral features 16 I/O ports that are divided into eight push-pull outputs and eight inputs
• Manufacturer: Maxim

Set the port output low to light the LED. Choose the
resistor value according to the following formula:
where:
R
LED (Ω).
V
(V).
V
V
sinking I
I
For example, to operate a 2.2V red LED at 10mA from
+5V supply:
I
and Eight Inputs
16
LED
SUPPLY
LED
OL
LED
2
C Port Expander with Eight Push-Pull Outputs
is the desired operating current of the LED (A).
______________________________________________________________________________________
is the output low voltage of the MAX7324 when
is the forward voltage of the LED (V).
is the resistance of the resistor in series with the
LED
R
is the supply voltage used to drive the LED
R
LED
LED
(V).
= (V
= (5 - 2.2 - 0.1) / 0.01 = 270Ω
SUPPLY
- V
LED
- V
OL
) / I
LED
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.
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.
Driving Load Currents Higher than 20mA
Power-Supply Considerations