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DS90C401: Customer needs help with circuit configuration and subsequent part failure

Gabriel Garza45
Intellectual 2275 points
Part Number: DS90C401
Other Parts Discussed in Thread: DS90C402,

Hello,

We have a customer who is having issue with both the DS90C401 and DS90C402.

From customer:

"I killed my first driver. Receiver seems OK.

I built a driver to receiver prototype using two SOIC-8 adapters,
with 6-ft tw-pr cable. It failed, all flat, output at gnd.

Setup:
- measured quick pin resistances, for reference before putting chips on adapters.
- verified pin resistances after chips are on adapters: all ok
- used 6-foot twisted pair from Driver to Receiver
- used same 5VDC & Gnd to both chips
- connections:
  pin-7 (DO2+) to receiver pin-7  (RI2+)
  pin-6 (DO2-) to receiver pin-8  (RI2-)
  100-ohms across receiver pins 7 to 8
  tied driver pin-4 (DI-1) to Gnd
  pins-2(RO1), 3(RI1+), 4(RI1-) left open per datasheet
  pin-6 (RO2) observed with 1-Meg-probe
 
- I applied 1.5v, 500ns pulse @ 50kpps to pin 8 (DI2)
  Receiver output stayed flat.
 
- quick pin resistance measurements made with SOIC-8 adapters removed from proto-board
DS90C401 pins before test:
Pin-1 to pin-2: 480k
Pin-2 to pin-3: 5.9M
Pin-3 to pin-4: 6M
Pin-4 to pin-5: 340k
Pin-5 to pin-6: 1.3Mk
Pin-6 to pin-7: 4.9M
Pin-7 to pin-8: 5.9M

DS90C401 pins after test:
Pin-1 to pin-2: 480k
Pin-2 to pin-3: 840k
Pin-3 to pin-4: 850k
Pin-4 to pin-5: 340k
Pin-5 to pin-6: 480k
Pin-6 to pin-7: 830k
Pin-7 to pin-8: 830k

DSC90C402 pins, measured same before and after test.
DS90C402 pins:
Pin-1 to pin-2: 475k
Pin-2 to pin-3: 6.7M
Pin-3 to pin-4: 6.7M
Pin-4 to pin-5: 327k
Pin-5 to pin-6: 4.8M
Pin-6 to pin-7: 6.6M
Pin-7 to pin-8: 6.6M

I really would appreciate your thoughts on what I have done wrong."

Can anyone assist with this?

Thank you,

Gabe Garza

TI Customer Support

  • 0
    TI__Intellectual 2915 points
    Hi,

    We will review this and provide an update to you on Monday.

    Dennis
  • 0
    TI__Mastermind 43795 points
    Hi Gabe,

    The 1.5V input does not meet the VIH minimum voltage level. I would try to run the test with a 0V - 5V input pulse to ensure the driver input was getting enough voltage to switch.

    Regards,
    Lee
  • 0 in reply to Lee Sledjeski
    TI__Intellectual 2275 points
    Hi Lee,

    We received a response from the customer:

    "If that could explain why my DS90C401 died, I would try it.
    But switching from 0v (V-IL) to only 1.5v (V-IH), doesn't explain why the DS90C401 died.
    I don't want to kill another DS90C401."

    Are there any further suggestions we could provide?

    Thanks,
    Gabe
  • 0 in reply to Gabriel Garza45
    TI__Intellectual 2275 points
    Hello,
    The customer replied with an additional question:

    "The DS90C402 datasheet has some vague statements wrt 401=>media=>402 pair.
    How well matched does the media and termination resistor need to be?
    According to the top of page-4,(DS90C402 datasheet), these 3 are said:

    -"The receiver is connected to the driver through a balanced
    media which may be a standard twisted pair cable, a parallel pair cable or simple PCB traces."

    -"...typically the characteristic impedance (Zo) of the media is in the range of 100-ohms."

    -"A termination resistor of 100-ohms should be selected to match the media, and is
    located as close to the receiver pins as possible."

    So...
    Can an 'acceptable range' be clarified more specifically for the media Zo & the resistor?
    i.e. what is the acceptable Zo range of the media, with 100-ohms at the receiver?

    Or, what is the acceptable range for the receiver resistor, with a media of 90-ohms ?
    Can the resistor be chosen (from 100 to 50 ohms) to match the media ?

    The Zo of twisted pair cables varies quite a bit (45 to 100+ ohms).
    I used the 100-ohm resistor at the Rcvr, and cut some tw-pair media to 6-ft, and tried it.
    My tw-pr media could have been 50-60 ohms,
    could that have killed the DS90C401 driver ?"


    Thank you,
    Gabe Garza
    TI Customer Support
  • 0 in reply to Gabriel Garza45
    TI__Mastermind 43795 points

    Gabe,

    The media type did not kill the driver.  My response about a 1.5V input just relates to the VIH minimum.  If the input never actually gets to VIH, then the output is very likely to stay "low" and not switch "high". 

    If the driver is "killed", it was likely some sort of EOS event.  I see the leakage has gone up, but the part is not completely shorted either.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    TI__Intellectual 2275 points
    Hi Lee,

    We received a response from the customer:

    "Yes, thank you very much for your help, and for the help from your e2e support team.

    I changed my media to a known 75-ohm impedance and installed a fresh DS90C401.
    It is working well now."

    Thanks for your help!

    Best regards,
    Gabe Garza
    TI Support