Datasheet

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-
limiting resistor (R
LED
). Set the port output low to
illuminate 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 MAX7321 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.
Figure 9. MAX7321 I/O Structure
P0–P7
PULLUP
ENABLE
INPUT
OUTPUT
40kΩ
MAX7321
V+
V+
I
2
C
CONTROL
P0
P3
P2
P1
P4
P5
P6
P7
INT
I/O
PORTS
POWER-
ON RESET
INPUT
FILTER
RST
SDA
SCL
AD2
AD0
MAX7321
www.maximintegrated.com
Maxim Integrated │ 13
MAX7321 I
2
C Port Expander with 8 Open-Drain I/Os
Functional Diagram