PCA9535EC datasheet(13/20 Pages) ONSEMI

13 / 20 page

PCA9535E, PCA9535EC

http://onsemi.com

Interrupt Output

The open−drain interrupt output is activated when an I/O

pin configured as an input changes state. The interrupt is

deactivated when the input pin returns to its previous state

or when the Input Port register is read (see Figure 9). A pin

configured as an output cannot cause an interrupt. Since

each 8−bit port is read independently, the interrupt caused by

Port 0 will not be cleared by a read of Port 1 or the other way

around.

Remark: Changing an I/O from an output to an input may

cause a false interrupt to occur if the state of the pin does not

match the contents of the Input Port register.

APPLICATION INFORMATION

Figure 11. Typical Application

Device address configured as 0100 000xb for this example.

IO0_0, IO0_2, IO0_3 configured as outputs.

IO0_1, IO0_4, IO0_5 configured as inputs.

IO0_6, IO0_7, and IO1_0 to IO1_7 configured as inputs.

PCA9535E

IO0_0

IO0_1

SCL

SDA

VDD

(5 V)

MASTER

CONTROLLER

INT

IO0_2

VDD

AD2

AD1

AD0

VDD

GND

INT

10 k

SUB−SYSTEM 1

(e.g., temp

sensor)

IO0_3

INT

SUB−SYSTEM 2

(e.g., counter)

RESET

controlled

switch

(e.g.,

7SB or FST)

VDD

ENABLE

SUB−SYSTEM 3

(e.g., alarm system)

ALARM

IO0_4

IO0_5

IO0_6

DIGIT

NUMERIC

KEYPAD

VSS

10 k

2 k

IO0_7

IO1_0

IO1_1

IO1_2

IO1_3

IO1_4

IO1_5

IO1_6

IO1_7

SDA

SCL

100 k

(x3)

Minimizing IDD When the I/Os are Used to Control

LEDs

To use the PCA9535E I/Os to control LEDs, the I/Os are

normally connected to VDD through a resistor as shown in

Figure 11. The LED acts as a diode. When the LED is off,

the I/O VI is about 1.2 V less than VDD. The supply current,

IDD, increases as VI becomes lower than VDD.

For applications requiring low current consumption, such

as battery power applications, it is recommended that the I/O

pin voltages be greater than or equal to VDD when the LED

is off. This would minimize current consumption. Figure 12

shows a high value resistor in parallel with the LED.

Figure 13 shows VDD less than the LED supply voltage by

at least 1.2 V. Both of these methods maintain the I/O VI at

or above VDD and prevents additional supply current

consumption when the LED is off.

This concern does not occur for the PCA9535EC because

the PCA9535EC I/O pins are open−drain.

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