Datasheet

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 MAX7323
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 MAX7323 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 10. MAX7323 I/O Port Structure
I
2
C
CONTROL
O7
P4
P5
O6
P3
P2
O1
O0
INT
I/O
PORTS
POWER-
ON RESET
INPUT
FILTER
RST
SDA
SCL
AD2
AD0
MAX7323
PORTS
P2–P5
PULLUP
ENABLE
INPUT
OUTPUT
40kΩ
G
S
D
MAX7323
V+
V+
Figure 9. MAX7323 Push-Pull Output Port Structure
OUTPUT
V+V+
PORTS
O0, O1, O6, O7
MAX7323
Functional Diagram
www.maximintegrated.com
Maxim Integrated │ 13
MAX7323 I
2
C Port Expander with 4 Push-Pull
Outputs and 4 Open-Drain I/Os