specific uart application on txs0102

Hi, James,

Here is the feedback for your questions.

1) Since the 5v is not always powered, what is the best design? Since I only need UART when the 5v side is powered, I have tied the OE pin to grd (via a resistor) and 5v. therefore the OE will go high when the 5v is powered. 

[Junjie] your design is Ok. Also the part has the Vcc isolation feature, it is also ok when 5V is off while the OE is enabled.

   a) from the datasheet, it says "During operation, ensure that VCCA ≤ VCCB at all times.". Since my application requires 5v(VccB) to be off when not in use(thus Vcca>Vccb). Is Vcca>Vccb safe at non-operating condition?

[Junjie] our part TXS0102 has the Vcc isolation feature, which means when one of power is off, the output will be in high-impedance. it is no problem with VccB is off, while VccA is on. what the concern is to ensure VccA<=VccB in normal transfer operation.

    b) If the 5v is not powered, the OE is low and according to datasheet, the A1 and B1 pin goes to high impedance state. Is there any implication to the MCU UART pins on the 3.3v side? (assuming mcu tx is push pull and rx is open drain)

[Junjie] no any implication to the MCU side except some leakage current (Ioz), when OE is low or 5V is off, all the A ports connected to the MCU side are the high impedance state.

2) with the application described above, is there advantage/disadvantage of using TXB0102 compared to TXS0102?

[Junjie] For TXS0102, it can be used for both open drain and push pull, if use it, please check the interface voltage level, make sure the Vil, Vih, Vol and Voh can meet the requirement.

For TXB0102, it only can be used for push pull scenario, it can not used for open drain, please make sure the driver can provide 2mA source and sink current capability.  and still need to check the Vol and Voh is OK for the receiver.

For your requirement for the 5V power off, it doesn't matter to use TXB or TXS, both parts have the Vcc isolaton feature. if no open drain required and driver capability is enough,I prefer to use the TXB0102 since its Vil, and Vih is standard voltage level. no special notice on it.

Any futher thing, please let me know.

BR
Junjie  

Thanks Junjie, much of the doubt has been cleared now. I will definitely check into the voltage range again, currently it has been working great so far.

During the experiment these few days, I have occasionally power down 3.3v while the 5v and OE is on. From what you have explained, this seems to be still safe since the Vcc isolation will make the 3.3v io pin goes to high impedance, is that correct?