PCA9554CBS datasheet(11/36 Pages) NXP

11 / 36 page

PCA9554B_PCA9554C

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Product data sheet

Rev. 1 — 19 September 2012

11 of 36

NXP Semiconductors

PCA9554B; PCA9554C

Low-voltage 8-bit I2C-bus/SMBus low power I/O port

Application design-in information

8.1 Minimizing IDD when the I/Os are 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 11. Since 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.

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 12 and Figure 13 show typical solutions to minimizing 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. However, the PCA9554B/PCA9554C needs

no external resistors due to the integrated 100 k

 pull-up resistors.

Device address is 0100 000x for this example (PCA9554B).

P0, P2, P3 configured as outputs.

P1, P4, P5 configured as inputs.

(1) External resistors are not needed due to the internal weak pull-up resistors.

Fig 11. Typical application

PCA9554B

SCL

SDA

VDD

(3.3 V)

MASTER

CONTROLLER

SCL

SDA

INT

VDD

VSS

INT

10 kΩ

SUB-SYSTEM 1

(e.g., temp sensor)

INT

SUB-SYSTEM 2

(e.g., counter)

RESET

controlled

switch

(e.g., CBT device)

enable

VSS

002aah128

10 kΩ

2 kΩ

100 kΩ

(× 3)(1)

SUB-SYSTEM 3

(e.g., alarm system)

ALARM

VDD

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