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SN65LVDS388A: About Vcc Overshoot problem

Guru 19605 points
Part Number: SN65LVDS388A

Customer is evaluating SN65LVDS388A for single end output, but start to supply vcc and occur 5V-overshoot.

⇒device is damaged.

Schematic and waveform is attached below;

※Single end is not output(35 pin), Differencial input pin(1pin-2pin) are Open.

※Single end is output(32 pin), Differencial input pin(6pin-7pin) are Open.

Please let me know about three points below.

①I think that one of cause is Vcc inlush for fast startup.

 Is there recommended spec for Vcc start up time? 

②In fact, the above differencial input circuit is no connect to transmitter. (100Ω termination is connecting)

 Is these circuit no problem?

③If there find the other cause, please let me know.

Best regards,

Satoshi

  • Hi Satoshi-san,

    We will work on this thread and provide an update as soon as possible.

    Regards,
    I.K.
  • I.K-san

    Thank you for reply.
    I looking forward your update.

    Best regards,
    Satoshi
  • I.K-san

    Sorry, I found mistake point and additional information.
    Please see below.

    【Mistake point】
    ・Overshoot problem is occurred not Vcc but output signal.
     About above second waveform, but It is hard to see, during B1Y's second startup is occur 5V overshoot.
     (Overshoot is looked to straight yellow line)
    【Additional information】
    ・Vcc start up time: 10ms is occur problem, but 50ms~100ms is no problem.
    ・Problem is depend on output channel.
     ⇒35pin is damage, 32pin is above problem, 26pin is no problem, etc. (Vcc: 10ms condition)
    ・On the same test condition and 10ms Vcc startup, 1~4ch LVDS receiver are not occur overshoot.

    Question point is below again, please let me know
    ①I think that one of cause is Vcc inrush for fast startup.
     Is there recommended spec for Vcc start up time?
    ②In fact, the above differential input circuit is no connect from transmitter. (100Ω termination is connecting)
     Is these circuit no problem?
    ③If there find the other cause, please let me know.
    ④Is SN65LVDS388A have transient response spec for overshoot?

    Best regards,
    Satoshi
  • Hi Satoshi-san,

    Sorry but can you provide a clearer image of the schematic? It is very blurry. I will continue looking into your questions but unfortunately, if it's not on the datasheet then I do not believe we have specs for Vcc start up time or transient response since this is an old device.

    Regards,
    I.K.
  • I.K-san

    Thank you for check.

    I pictured simplified schematic, please see attached below.

    By the way, customer added 10nF capacitor near VCC, waveform was not change.

    Best regards,

    Satoshi

  • Hi Satoshi-san,

    Please see update below:

    ①I think that one of cause is Vcc inrush for fast startup.
     Is there recommended spec for Vcc start up time?

    Unfortunately there is no recommended spec for this parameter. This issue appears on different channels on the same unit? Has the customer seen this issue on a different unit? 

    ②In fact, the above differential input circuit is no connect from transmitter. (100Ω termination is connecting)
     Is these circuit no problem?

    This circuit looks okay; don't see any problems. 


    ④Is SN65LVDS388A have transient response spec for overshoot?

    Unfortunately, there is no recommended spec for this parameter.

    Regards,

    I.K.

  • I.K-san

    Thank you for update.

    I updated your answer ①, please see below.

    This issue appears on different channels on the same unit?
    ⇒Yes, this issue is appear the same unit.
     But issue degree is depend on channel; large issue, small issue, and one channel was no issue.

    Has the customer seen this issue on a different unit?
    ⇒Yes, customer checked different unit. result was near the other unit.

    Best regards,
    Satoshi
  • Hi Satoshi-san,

    Since the issue appears on multiple units and the results were similar, I agree that the cause is the Vcc inrush for fast startup. Since there is no recommended spec for Vcc startup, I believe the customer should keep it in the range where they see no issues on any channels or units.

    Regards,
    I.K.
  • I.K-san

    Thank you for reply, I understood.
    I will feedback to customer.

    Best regards,
    Satoshi