NXP octal SMBus registered
interface PCA9557
Convenient parallel I/O expansion
or collection via the I
2
C/SMBus
This flexible device offloads the I/O controller in a range of system-management applications.
It uses the I
2
C/SMBus for I/O expansion or collection, supports unique resets, enables chipset-to-
peripheral interfaces, and can be used to send alert signals to LEDs.
Features
Ñ
Supports SMBus or I
2
C-bus I/O expansion and collection
Ñ
Supports simple BIOS implementation via four registers
Ñ
Input port enables light load readback
Ñ
Active-high polarity inversion port inverts inputs
Ñ
Configuration port sets I/O as inputs or outputs
Ñ
Outpur port allows readback for debug
Ñ
I/O open-drain output for interrupt generatoin
Ñ
Active-low reset and power-recycle defaults all I/O to inputs
Ñ
Three address pins enable up to eight devices (64 I/O)
Ñ
Glitch-free operation on power-up and power-down
Ñ
2.3- to 5.5-V operation to 400 kHz
Ñ
16-pin plastic SO, TSSOP, and HVQFN packages
Applications
Ñ
Mobile system management
Ñ
Desktop workstation or server system management
Ñ
Alert-on-Lan (AoL) applications
Ñ
BIOS signalling with FlexATX EasyPC diagnostic code
The PCA9557 has its own reset pins, so its I/O can be reset
without taxing the I/O controller’s GPIO. This is especially
useful when only a subset of the system I/O need to be reset.
The V
DD
can be supplied independently from the I/O
controller’s power, so it can operate even when the I/O
controller is off. To capture and submit any pre-system
power-alert signals, it’s recommended that a collector and an
indicator be kept active while the I/O controller is off.
The PCA9557’s indicator interrupts are typically configured
as open drain, so they can be wire-OR’d with other indicator
interrupts. The I/O pin can also be set as an open-drain
output, to support an interrupt.
To facilitate BIOS implementation, the PCA9557 has four
SMBus registers.
In system-management configurations that use
the popular application “Alert-on-Lan” or AoL, the
PCA9557 can provide motherboard alert signals via
the I
2
C/SMBus and thereby save the I/O controller
from using its limited GPIO for I/O-intensive system-
management functions. The PCA9557 can be used
to collect a range of motherboard signals, including
chassis intruder, CPU missing, voltage regulator
module power good, and SMBus environmental IC
alert. It can also drive a range of signals, including
reset button switch and power button switch.
The simple, two-wire I
2
C/SMBus structure enables
a minimal pin-count interface between the
motherboard and various peripherals, such as a
PCI card or a laptop docking station. The PCA9557
can also be used to support AoL applications by
configuring its parallel interface to supply alert signals
to the system’s LEDs.
Similarly, in applications that use FlexATX Easy PC
diagnostic code, the PCA9557 can be used with LEDs
to signal BIOS power-up with lights instead of beeps.
Selection guide
SO
Tube
T&R
PCA9557D
PCA9557D-T
PCA9557 block diagram
TSSOP
PCA9557PW
PCA9557PW-T
HVQFN
-
PCA9557BS-T
Pinout diagram
Sample application for mobile system management
Sample application for desktop workstation
or server system management
www.nxp.com/i2clogic
www.nxp.com
© 2008 NXP B.V.
All rights reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner.
The information presented in this document does not form part of any quotation or contract, is believed to be accurate and
reliable and may be changed without notice. No liability will be accepted by the publisher for any consequence of its use.
Publication thereof does not convey nor imply any license under patent- or other industrial or intellectual property rights.
Date of release: August 2008
Document order number: 9397 750 16534
Printed in the Netherlands
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