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TXB0104: Customer is seeing garbled data

Part Number: TXB0104

Hi Support team, 

My customer is using the TXB0104 to interface two different device via UART. They are getting garbled data.One issue may be the OE, it is tied to VCCB, another may be the decoupling, see attached schematic. 

Can you look at the schematic and let me know if there is anything in error, concerns, 

Here are my customer comments

We are having some issues with the TXB0104 in a product. 

The TXB0104 is acting as a UART level translator between an STM32F101CBU6 and a Qualcomm Q410e System on module.

The STM32F101 operates at 3.3V, the Q410e operates at 1.8V.

Attached is a schematic snippet of how the TXB0104 is being used.

Please review it and let me know if there is something obvious that I missed.  The problem is that we are getting scrambled data periodically.

The BLSP1 refers to the Qualcomm Q410 interface and the USART2_TX and USART2_RX refer to the STM32 UART interface.

DS-Mars.docx

I'm reading through the datasheet more carefully.  It looks like OE is internally referenced to VCCA (the 1.8V side)  I have it tied to VCCB (the 3.3V side).  According to the datasheet OE can take up to 5.5V.  OE must be driven high for the outputs to operate.

Elsewhere in the datasheet it mentions that OE must be driven low until VCCA and VCCB are stable.

It is likely that VCCB (3.3V side) receives power before VCCA (1.8V side) in my application.

So I have to ask the following:

What happens to the TXB0104 when OE is tied to VCCB, and what can happen if OE is always tied to VCCB including on power up? 

I'm trying to determine if the part will be damaged or will get damaged overtime, etc. or what will happen?

  • Hi Jeff,
    I've notified the appropriate apps specialist and he should be back with you soon.
  • Hi Jeff,

    Thanks for your query and sorry I missed your post yesterday.

    You are right, OE is referenced to Vcca and should not be tied to Vccb. could this be the reason why the garbled data is being seen, I do not think so since OE pin is overvoltage tolerant and hence having higher than Vcca is ok.
    Power sequencing is our recommendations but not requirements. Customers have tied the OE pin directly to Vcca to have the device always enabled without issues.
  • Although the schematic sent out is blurry, I do not see any obvious mistakes on it.
    If you could, please send out scopeshots of the garbled data being seen with the Vcca / Vccb and input signal if possible.