PCA6408APW datasheet(13/40 Pages) NXP

13 / 40 page

PCA6408A

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 1 — 27 September 2012

13 of 40

NXP Semiconductors

PCA6408A

Low-voltage, 8-bit I2C-bus and SMBus I/O expander

Application design-in information

9.1 Minimizing IDD when I/Os control LEDs

When the I/Os are used to control LEDs, normally they are connected to VDD(P) through a

resistor as shown in Figure 12. The LED acts as a diode, so when the LED is off, the I/O

VI is about 1.2 V less than VDD(P). The IDD parameter in Table 15 “Static characteristics”

shows how IDD(P) increases as VI becomes lower than VDD(P). Designs that must minimize

current consumption, such as battery power applications, should consider maintaining the

I/O pins greater than or equal to VDD(P) when the LED is off.

Figure 13 shows a high-value resistor in parallel with the LED. Figure 14 shows VDD(P)

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(P) and prevent additional supply current consumption when the LED

is off.

Device address configured as 0100 000x for this example.

P0 and P2 through P4 are configured as inputs.

P1 and P5 through P7 are configured as outputs.

(1) Resistors are required for inputs (on P port) that may float. If a driver to an input will never let the

input float, a resistor is not needed. Outputs (in the P port) do not need pull-up resistors.

Fig 12. Typical application

PCA6408A

SCL

SDA

VDD

SCL

SDA

VSS

MASTER

CONTROLLER

VSS

VDD(I2C-bus) = 1.8 V

controlled

switch

enable

INT

VDD(P)

INT

10 kΩ

SUBSYSTEM 1

(e.g., alarm system)

ALARM(1)

10 kΩ

RESET

VDD(P)

002aaf829

VDD(I2C-bus)

ADDR

KEYPAD

10 kΩ

10 kΩ (× 3)

PCA6408APW Datasheet(PDF) 13 Page - NXP Semiconductors

PCA6408APW Datasheet(HTML) 13 Page - NXP Semiconductors

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Datasheet Download

Link URL