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Original question:

THS3001: THS3001HV oscillates at higher temperatures

THS3001: Different operating wave forme due to LOT differences

Masayuki Uchihara
Intellectual 1686 points
Part Number: THS3001
Other Parts Discussed in Thread: THS3491

Tool/software:

Hi Team,

My customer build a circuit using the THS3001 however the waveforme is different. the differences are only LOT accourding to cusomter.

Can you advise why the differences happend? 

>>> Customer questio & Request>>>

The square wave is input at 5kHz, ±5V, and a square wave of 50mV (reduced to 1/100) should be output by capacitive voltage division (see output voltage).
The square wave is distorted depending on the production lot (this has not been observed in simulations). I would like to know the cause of the distortion.

Best Regards,

Masa

  • 0
    TI__Genius 14640 points

    Hi Masa,

    I was able to simulate the circuit and got a similar result as the square wave the customer is seeing.  Could you try reducing the input resistor to 100k instead of the 2.4MOhm on the board. If you adjust this resistor for the lot giving you a square output, do you see the signal behave more like the other signals? 

    Best Regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    TI__Intellectual 1686 points

    Hi Ignacio,

    Thank you for your reply. I'll take with customer. Which parameter of this amplifer is related with the input resistor? If I can explain it based on the datasheet spec, it would be really helpful.

    Best Regards,

    Masa

  • 0 in reply to Masayuki Uchihara
    TI__Genius 14640 points

    Hi Masa,

    The concern with the very large input resistor on the non-inverting pin is due to the non-inverting input bias current. The device has a max value of 15uA across temperature, which would cause an offset at the output. Due to lot variation one possible scenario is that some units are not as affected by the large resistance, but others could have a larger bias current which could be causing the device to fall outside its linear region. Decreasing this resistance value would be a good debug step to see if the circuit performance changes. 

    Best regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    TI__Intellectual 1686 points

    Hi Ignacio,

    Is there die different towards the lot differences? I think this device has PCN in the past.

    Is there any input resistance differences bewtween before after PCN? Because the THS3491 has lower input resistance value than THS3001?

    Best Regards,

    Masa

  • 0 in reply to Masayuki Uchihara
    TI__Genius 14640 points

    Hi Masa,

    There was a PCN issued as we transitioned to a new fab process. I was able to compare and found the inverting and non-inverting impedance did not change. The THS3491 is a very different device to the THS3001, so I am not sure we can compare the two devices. Was the customer able to adjust the resistor at the input? 

    Best Regards,

    Ignacio