Datasheet

PCA9517_3 © NXP B.V. 2007. All rights reserved.
Product data sheet Rev. 03 — 30 January 2007 4 of 19
NXP Semiconductors
PCA9517
Level translating I
2
C-bus repeater
be able to rise to 0.5 V until the A-side rises above 0.3V
CCA
, then the B-side will continue
to rise being pulled up by the external pull-up resistor. The V
CCA
is only used to provide
the 0.3V
CCA
reference to the A-side input comparators and for the power good detect
circuit. The PCA9517 logic and all I/Os are powered by the V
CCB
pin.
6.1 Enable
The EN pin is active HIGH with an internal pull-up to V
CCB
and allows the user to select
when the repeater is active. This can be used to isolate a badly behaved slave on
power-up until after the system power-up reset. It should never change state during an
I
2
C-bus operation because disabling during a bus operation will hang the bus and
enabling part way through a bus cycle could confuse the I
2
C-bus parts being enabled.
The enable pin should only change state when the global bus and the repeater port are in
an idle state to prevent system failures.
6.2 I
2
C-bus systems
As with the standard I
2
C-bus system, pull-up resistors are required to provide the logic
HIGH levels on the buffered bus (standard open-collector configuration of the I
2
C-bus).
The size of these pull-up resistors depends on the system, but each side of the repeater
must have a pull-up resistor. This part designed to work with Standard mode and Fast
mode I
2
C-bus devices in addition to SMBus devices. Standard mode I
2
C-bus devices only
specify 3 mA output drive; this limits the termination current to 3 mA in a generic I
2
C-bus
system where Standard mode devices and multiple masters are possible. Under certain
conditions higher termination currents can be used.
Please see Application Note AN255, I
2
C/SMBus Repeaters, Hubs and Expanders for
additional information on sizing resistors and precautions when using more than one
PCA9517 in a system or using the PCA9517 in conjunction with other bus buffers.