PCA9509 Просмотр технического описания (PDF) - Philips Electronics
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PCA9509 Datasheet PDF : 16 Pages
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Philips Semiconductors
PCA9509
Level translating I2C-bus/SMBus repeater
pull-down driver is enabled until port A rises above approximately 0.15 V (VILc), then
port B, if not externally driven LOW, will continue to rise being pulled up by the external
pull-up resistor.
Remark: Ground offset between the PCA9509 ground and the ground of devices on
port A of the PCA9509 must be avoided.
The reason for this cautionary remark is that a CMOS/NMOS open-drain capable of
sinking 3 mA of current at 0.4 V will have an output resistance of 133 Ω or less (R = E / I).
Such a driver will share enough current with the port A output pull-down of the PCA9509
to be seen as a LOW as long as the ground offset is zero. If the ground offset is greater
than 0 V, then the driver resistance must be less. Since VILc can be as low as 90 mV at
cold temperatures and the low end of the current distribution, the maximum ground offset
should not exceed 50 mV.
Bus repeaters that use an output offset are not interoperable with the port A of the
PCA9509 as their output LOW levels will not be recognized by the PCA9509 as a LOW. If
the PCA9509 is placed in an application where the VIL of port A of the PCA9509 does not
go below its VILc it will pull port B LOW initially when port A input transitions LOW but the
port B will return HIGH, so it will not reproduce the port A input on port B. Such
applications should be avoided.
Port B is interoperable with all I2C-bus slaves, masters and repeaters.
6.1 Enable
The EN pin is active HIGH 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 I2C-bus operation because disabling during
a bus operation will hang the bus and enabling part way through a bus cycle could
confuse the I2C-bus parts being enabled.
The enable pin should only change state when the bus and the repeater port are in an idle
state to prevent system failures.
6.2 I2C-bus systems
As with the standard I2C-bus system, pull-up resistors are required to provide the logic
HIGH levels on the buffered bus (standard open-collector configuration of the I2C-bus).
The size of these pull-up resistors depends on the system. Each of the port A I/Os has an
internal pull-up current source and does not require the external pull-up resistor. Port B is
designed to work with Standard-mode and Fast-mode I2C-bus devices in addition to
SMBus devices. Standard-mode I2C-bus devices only specify 3 mA output drive; this
limits the termination current to 3 mA in a generic I2C-bus system where Standard-mode
devices and multiple masters are possible. Under certain conditions higher termination
currents can be used.
PCA9509_1
Product data sheet
Rev. 01 — 27 June 2006
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
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