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TRS3232E: Question about datarate

Roy Hsu
Genius 9180 points
Part Number: TRS3232E
Other Parts Discussed in Thread: TRSF3232E

Hi there,

I am trying to replace Exar SP3232EB with our TRS3232EI and my customer has one concern on the datarate.

In SP3232EB datasheet, the minimum value of the maximum datarate is 250 kbps.

However, the datarate is shown as 150 kbps(min.) and 250 kbps(typ.) which says that our datarate could be in the range of 150 kbps to 250 kbps.

My customer is concerned about this since they need the datarate to be higher than 250 kbps.

Is it just related to the way of defining the spec or our device just behaves this way?

Thanks!

Roy Hsu

  • 0
    TI__Mastermind 25705 points

    Roy,

    I think the two devices have similar performance at 250kbps, although the datasheet specifies it differently. If your customer wants to support a higher data rate, you can recommend TRSF3232E (www.ti.com/.../trsf3232e.pdf) that has minimum 1Mbps data rate. Please let me know if you have more questions.

    Regards,

    Hao

  • 0 in reply to Hao L
    TI__Genius 9180 points

    Hi Hao,

    Is there any way to verify this through bench test?

    By 250 kbps (typ.), it means that a certain portion of this device would support 250 kbps but some would not.

    Is there a way to show that this device work well at 250 kbps?

    If there's any material or test result, please send it to me via email.

    Thanks!

    Best regards,

    Roy Hsu

  • 0 in reply to Roy Hsu
    TI__Mastermind 25705 points

    Roy,

    Yes we could test several devices, but probably we won't see the process variation due to limited samples. If a device doesn't support 250kbps, it can still communicate but might be short on some spec like output voltage. These behavior is a statistical spread over the voltage, temperature and process.

    Regards,

    Hao

  • 0 in reply to Hao L
    TI__Genius 9180 points

    Hi Hao,

    We have decided to switch to TRSF3232EI. Now, the capacitor values for different Vcc are different.

    Why is that? Is it OK to use 4 0.1 uF caps for 5V Vcc?

    If not, what effect will it bring?

    Thanks!

    Roy Hsu

  • 0 in reply to Roy Hsu
    TI__Mastermind 25705 points

    Roy,
    The capacitor values impact the ripple of the output voltage. You can take a look at this post for some details (e2e.ti.com/.../463809). The rule of thumb is that if the flying cap C1 is smaller and the storage cap C3 is bigger, the ripple is smaller. Therefore we recommend different values for 5V supply.
    Regards,
    Hao

  • 0 in reply to Hao L
    TI__Genius 9180 points
    Hi Hao,

    There's some problem with the link so I can't see the post.

    Besides, how would the ripple impact the performance?

    Looking at Exar SP3222 datasheet, the external capacitors for 5V Vcc are all 0.1 uF.

    This difference actually makes my customer reluctant to switch to our device.

    Thanks!

    Roy Hsu
  • 0 in reply to Roy Hsu
    TI__Mastermind 25705 points

    Roy,

    (sorry for the broken link. I fixed it.)

    It's OK to use 0.1uF cap, with the drawback of higher ripples. Many customers prefer to have less ripples for better signal quality such as less emi.

    To give you visual comparison, I attach two waveforms here.

    You can tell the second graph has bigger ripples.

    Please let me know if you have more questions.

    Regards,

    Hao 

  • 0 in reply to Hao L
    TI__Genius 9180 points
    Hi Hao,

    Thanks for showing the waveforms! That really helps!

    However, I can see some ringing at the falling slope of the first graph and am wondering if that harms data transmission or emi performance?

    Besides, from the link you shared, I saw a statement saying "The ripple voltage does not hurt the data transmission."

    Therefore, I think 4x0.1uF should be fine if the customer can bear with the resulted emi performance but will also suggest them to follow the recommendation in the datasheet.

    Thanks!
    Roy Hsu
  • 0 in reply to Roy Hsu
    TI__Mastermind 25705 points

    Roy,

    The falling slope should not impact data transmission since the voltage level is above 5V (RS232 standard). I agree with your comments. Please let me know if your customer has any questions or concerns.

    Regards,

    Hao