PCA9538D datasheet(8/18 Pages) PHILIPS

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Philips Semiconductors

Product data sheet

PCA9538

8-bit I2C and SMBus low power I/O port

with interrupt and reset

2004 Oct 05

TYPICAL APPLICATION

SW02180

I/O0

I/O1

I/O2

I/O3

I/O4

I/O5

I/O6

I/O7

VDD

(5 V)

VDD

SCL

SDA

INT

RESET

MASTER

CONTROLLER

GND

SCL

SDA

PCA9538

VSS

VDD

SUBSYSTEM 3

(e.g. alarm

system)

SUBSYSTEM 2

(e.g. counter)

SUBSYSTEM 1

(e.g. temp sensor)

INT

VDD

ALARM

Controlled Switch

(e.g. CBT device)

ENABLE

10 k

Ω

10 k

Ω

10 k

Ω

2 k

Ω

NOTE: Device address configured as 1110000 for this example

I/O0, I/O2, I/O3, configured as outputs

I/O1, I/O4, I/O5, configured as inputs

I/O06, I/O7, are not used and need 100 kΩ pull-up resistors to protect them from floating.

10 k

Ω

INT

IRESET

100 k

Ω

(

×3)

Figure 10. Typical application

Minimizing IDD when the I/O is used to control LEDs

When the I/Os are used to control LEDs, they are normally connected to VDD through a resistor as shown in Figure 10. Since the LED acts as a

diode, when the LED is off the I/O VIN is about 1.2 V less than VDD. The supply current , IDD, increases as VIN becomes lower than VDD and is

specified as

∆IDD in the DC characteristics table.

Designs needing to minimize current consumption, such as battery power applications, should consider maintaining the I/O pins greater than or

equal to VDD when the LED is off. Figure 11 shows a high value resistor in parallel with the LED. Figure 12 shows VDD less than the LED supply

voltage by at least 1.2 V. Both of these methods maintain the I/O VIN at or above VDD and prevents additional supply current consumption when

the LED is off.

VDD

LEDx

LED

100 k

Ω

SW02086

Figure 11. High value resistor in parallel with the LED

VDD

3.3 V

LEDx

LED

SW02087

5 V

Figure 12. Device supplied by a lower voltage

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