PCA9509PDP,118 View Datasheet(PDF) - NXP Semiconductors.
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PCA9509PDP,118 Datasheet PDF : 26 Pages
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NXP Semiconductors
PCA9509P
Low power level translating I2C-bus/SMBus repeater
6. Functional description
Refer to Figure 1 “Functional diagram of PCA9509P”.
The PCA9509P enables I2C-bus or SMBus translation down to VCC(A) as low as 0.8 V
without degradation of system performance. The PCA9509P contains 2 bidirectional
open-drain buffers specifically designed to support up-translation/down-translation
between the low voltage and 3.3 V SMBus or 5 V I2C-bus. The port A and port B I/Os are
over-voltage tolerant to 5.5 V even when the device is unpowered.
The PCA9509P includes a power-up circuit that keeps the output drivers turned off until
VCC(B) is above 1.7 V and the VCC(A) is above 0.7 V. VCC(B) and VCC(A) can be applied in
any sequence at power-up. After power-up and with the EN pin HIGH, a LOW level on
port A (below approximately 0.15VCC(A)) turns on the corresponding port B driver (either
SDA or SCL) and drives port B down to about 0 V. When port A rises above approximately
0.15VCC(A), the port B pull-down driver is turned off and the external pull-up resistor pulls
the pin HIGH. When port B falls first and goes below 0.3VCC(B), the port A driver is turned
on and port A pulls down to 0.2VCC(A) (typical). The port B pull-down is not enabled unless
the port A voltage goes below VIL. If the port A low voltage goes below VIL, the port B
pull-down driver is enabled until port A rises above approximately 0.15VCC(A) (VIL), then
port B, if not externally driven LOW, rises, being pulled up by the external pull-up resistor.
When port B voltage rises above 50 % of VCC(B), port A continues to rise being pulled up
by external pull-up resistor.
Remark: Ground offset between the PCA9509P ground and the ground of devices on
port A of the PCA9509P 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 has an output resistance of 133 or less (R = E / I). Such
a driver shares enough current with the port A output pull-down of the PCA9509P 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 VIL can be as low as 80 mV at cold
temperatures and the low end of the current distribution, the maximum ground offset
should not exceed 40 mV.
Bus repeaters that use an output offset are not interoperable with the port A of the
PCA9509P as their output LOW levels are not recognized by the PCA9509P as a LOW. If
the PCA9509P is placed in an application where the VIL of port A of the PCA9509P does
not go below its VIL, the port B does not go LOW.
Port B provides normal I2C-bus voltage levels and 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 hangs the bus and enabling part way through a bus cycle could confuse
the I2C-bus parts being enabled. The EN also puts the PCA9509P in a standby condition
to reduce power consumption.
PCA9509P
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 4 — 18 May 2018
© NXP B.V. 2018. All rights reserved.
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