MAX7321 Maxim, MAX7321 Datasheet - Page 13

• Manufacturer Part Number: MAX7321
• Description: The MAX7321 2-wire serial-interfaced peripheral features eight open-drain I/O ports with selectable internal pullups and transition detection
• Manufacturer: Maxim

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
nate the LED. Choose the resistor value according to
the following formula:
where:
R
LED (Ω).
V
V
V
sinking I
I
For example, to operate a 2.2V red LED at 10mA from a
+5V supply:
LED
SUPPLY
LED
LED
OL
is the desired operating current of the LED (A).
is the output-low voltage of the MAX7321 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 (V).
R
LED
LED
(V).
= (5 - 2.2 - 0.07) / 0.010 = 270Ω.
= (V
I
LED
2
______________________________________________________________________________________
SUPPLY
C Port Expander with 8 Open-Drain I/Os
. Set the port output low to illumi-
- V
SDA
SCL
RST
LED
AD0
AD2
Driving LED Loads
- V
OL
) / I
INPUT
FILTER
ON RESET
POWER-
LED
MAX7321
CONTROL
I
2
C
Figure 9. MAX7321 I/O Structure
OUTPUT
PULLUP
ENABLE
INPUT
PORTS
I/O
V+
V+
Functional Diagram
P7
P6
P5
P4
P3
P2
P1
P0
INT
40kΩ
MAX7321
P0–P7
13