PCA9517A_14 Datasheet, PDF (3/14 Pages) ON Semiconductor – Level-Translating I2C-Bus Repeater

PCA9517A
PIN ASSIGNMENT
PCA9517A
Figure 2. SOIC8 / Micro8
PIN DESCRIPTIONS
Symbol
Pin
V_CC(A)
1
SCLA
2
SDAA
3
GND
4
EN
5
SDAB
6
SCLB
7
V_CC(B)
8
Description
A−Side Supply Voltage (0.9 V to 5.5 V)
Open−Drain I/O, Serial Clock A−Side Bus
Open−Drain I/O, Serial Data A−Side Bus
Ground
Active−HIGH Repeater Enable
Open−Drain I/O, Serial Data B−Side Bus
Open−Drain I/O, Serial Clock B−Side Bus
B−Side Supply Voltage (2.7 V to 5.5 V)
FUNCTIONAL DESCRIPTION
Please refer to Figure 1 “Block Diagram of PCA9517A”.
The PCA9517A enables I²C−bus or SMBus translation
down to V_CC(A) as low as 0.9 V without degradation of
system performance. The PCA9517A contains two
bidirectional open−drain buffers specifically designed to
support up−translation/down−translation between the low
voltage (as low as 0.9 V) and a 3.3 V or 5 V I²C−bus or
SMBus. All inputs and I/Os are overvoltage tolerant to 5.5 V
even when the device is unpowered (V_CC(B) and/or V_CC(A)
= 0 V). The PCA9517A includes a power−up circuit that
keeps the output drivers turned off until V_CC(B) is above
2.5 V and the V_CC(A) is above 0.8 V. V_CC(B) and V_CC(A) can
be applied in any sequence at power−up.
After power−up and with the enable (EN) HIGH, a LOW
level on port A (below 0.3 V_CC(A)) turns the corresponding
port B driver (either SDA or SCL) on and drives port B down
to about 0.5 V. When port A rises above 0.3 V_CC(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 0.3V_CC(B), the port A driver is turned on and port A
pulls down to 0 V. The port B pull−down is not enabled
unless the port B voltage goes below 0.4 V. If the port B low
voltage does not go below 0.5 V, the port A driver will turn
off when port B voltage is above 0.7 V_CC(B). If the port B
low voltage goes below 0.4 V, the port B pull−down driver
is enabled and port B will only be able to rise to 0.5 V until
port A rises above 0.3 V_CC(A), then port B will continue to
rise being pulled up by the external pull−up resistor. The
V_CC(A) is only used to provide the 0.3 V_CC(A) reference to
the port A input comparators and for the power good detect
circuit. The PCA9517A logic and all I/Os are powered by
the V_CC(B) pin.
Enable Pin (EN)
The EN pin is active HIGH with an internal pull−up to
V_CC(B) 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 EN pin should only change state when the global bus
and the repeater port are in an idle state to prevent system
failures.
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,
but each side of the repeater must have a pull−up resistor.
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