PCA9306 used as a I2C Switch. No Voltage translation

Steve W1

Other Parts Discussed in Thread: PCA9306, TXS0102

I'm using your PCA9306 but don't require the voltage translation aspect in that I have VREF1 and VREF2 both connected to 3.3V (however different sources so that VREF2 can be on while VREF1 is off), and I have the EN connected to a pull-down and controlled by one processor (related to VREF1) while the other processor on the board is related to VREF2. Will this still work as a bidirectional tristate I2C buffer satisfactorily ? Thanks, -Steve

over 10 years ago

0 Jonathan Valdez over 10 years ago

TI__Genius 16565 points

Hello Steve,

Thanks for the question.

Would you be able to supply a schematic of your PCA9306 or a block diagram which highlights the connections?

If both power rails are 3.3 V and share the same ground, then you may actually leave VREF1 and VREF2 pins tied to ground and have EN controlled by a processor similar to what it sounds like your current setup is.

Also, I am moving this post to the I2C forum, which is the proper forum for support on this product.

0 ShreyasRao over 10 years ago in reply to Jonathan Valdez

TI__Guru 63250 points

Hi Steve ,
If you don't need the voltage translation with this device , why not use a bidirectional buffer or 3 state mux ?

0 Steve W1 over 10 years ago in reply to ShreyasRao

Prodigy 100 points

Here is the schematic:

0 Jonathan Valdez over 10 years ago in reply to Steve W1

TI__Genius 16565 points

Hello Steve,

Is it possible to leave either 1 or both of the VREF pins floating?

The reason is that when EN pin is at 3.3V and either VREF pin is low and the other is high, you will have an internal short between the two VREF pins. There is a MOSFET between the two VREF pins (which is why there is a 200k current limiting resistor used in the typical application schematic).

0 Steve W1 over 10 years ago in reply to Jonathan Valdez

Prodigy 100 points

I'm actually using a TXS0102 but trying to fix the I2C bus I'm connected to with a PCA9306 Breakout Board. Does the TXS0102 have the same issue when one of the VREF is on (= 3.3V) and the other might be off (= 0V) in terms of a short circuit ? I noticed that the datasheet allows VREF1 = VREF2 so I am assuming not ?

0 Jonathan Valdez over 10 years ago in reply to Steve W1

TI__Genius 16565 points

You are correct. the TXS0102 uses internal logic and does not have this connection. You can safely have one rail low and the other high.

0 Steve W1 over 10 years ago in reply to Jonathan Valdez

Prodigy 100 points

If one VREF were on while the other were off, what kind of leakage/ current draw would I expect with 3.3V ?

0 Jonathan Valdez over 10 years ago in reply to Steve W1

TI__Genius 16565 points

Steve,

You can find some information about this in the datasheet's electrical characteristics.

0 Steve W1 over 8 years ago in reply to Jonathan Valdez

Prodigy 100 points

Regarding the TXS0102DQMR chip, if VCCA is almost off (~ 0.5V) and the OE is pulled to GND with a resistor but VCCB is at 3.3V, will the 10K pullups associated with B1 and B2 be active ?

0 ShreyasRao over 8 years ago in reply to Steve W1

TI__Guru 63250 points

hi Steve ,

For the TXS0102 device, the I/O ports will be in Hi-z in the following conditions :

1) OE is held low(gnd) , as OE is active high enable for the device.
2) If either Vcc is held at gnd(not floating)

If you have engaged the OE pins , the I/O are in Hi-Z. (disconnected with the 10k pull up)

0 Steve W1 over 8 years ago in reply to ShreyasRao

Prodigy 100 points

So I guess my case qualifies for 1) so I/O is hi-Z and the internal 10K pullups then have an effect or have no effect ?

Is there an equivalent part in all respects that doesn't have internal 10K pullups, ie. none at all ?

0 ShreyasRao over 8 years ago in reply to Steve W1

TI__Guru 63250 points

For the TXS0102 , when OE is engaged , the 10k is disconnected and the i/os are Hi-Z.
There is TXB which is a weak driver without the 10k pullup internally and there is LSF as well in the auto bidirection family.
but do you need the internal 10k ? Are your signals OD or push pull ?

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PCA9306 used as a I2C Switch. No Voltage translation