MAX7321 datasheet(13/17 Pages) MAXIM

13 / 17 page

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 MAX7321

port, and the LED anode to V+ through the series cur-

rent-limiting resistor, RLED. Set the port output low to

illuminate the LED. Choose the resistor value according

to the following formula:

RLED = (VSUPPLY - VLED - VOL) / ILED

where:

RLED is the resistance of the resistor in series with the

LED (

Ω).

VSUPPLY is the supply voltage used to drive the LED (V).

VLED is the forward voltage of the LED (V).

VOL is the output-low voltage of the MAX7323 when

sinking ILED (V).

ILED is the desired operating current of the LED (A).

For example, to operate a 2.2V red LED at 10mA from a

+5V supply:

RLED = (5 - 2.2 - 0.07) / 0.010 = 270

Ω.

I2C Port Expander with 4 Push-Pull Outputs

and 4 Open-Drain I/Os

______________________________________________________________________________________

OUTPUT

V+

PORTS

O0, O1, O6, O7

MAX7323

Figure 9. MAX7323 Push-Pull Output Port Structure

PORTS

P2–P5

PULLUP

ENABLE

INPUT

OUTPUT

40k

MAX7323

V+

Figure 10. MAX7323 I/O Port Structure

I2C

CONTROL

INT

I/O

PORTS

POWER-

ON RESET

INPUT

FILTER

RST

SDA

SCL

AD2

AD0

MAX7323

Functional Diagram

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