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SN65HVD1782: Schematic Review Request

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Replies: 4

Views: 853

Part Number: SN65HVD1782

Hi there,

Would you be able to review the attached schematic for me? (RS485: SN65HVD1782, RS232: TRS3122)

Thank you!

Best regards,

Roy Hsu

  • Hi Roy,

    thank you for reaching out. From the first look I can't find any major issues or mistakes.

    For the RS-485 part:

    The only thing what catches my attention is that there is an external fail-safe network which is not necessary due to fact that the SN65HVD1782 has an internal fail-safe feature. Please take a look here to get more information:

    https://e2e.ti.com/support/interface/industrial_interface/f/142/p/640404/2362531#2362531

    Other than that I was looking at the current what is recommended for the TLP175A. The typical forward current is specified at 5 mA and with the current 330 Ohm resistor it would be 10 mA what is in the specs of the device.

    For the RS-232 part:

    Nothing wrong found here neither all caps look good TTL levels on the GPIO pins also.

    Please let me know if this is helping you out. Don't hesitatate to ask further questions.

    Kind regards 

    Dierk

  • In reply to Dierk Bronner:

    Hi Dierk,

    Yes, your response helps a lot. Thanks for the support!

    My customer has some other questions regarding the schematic:

    1.For the RS-485 circuit, do you mean that D1802/D1803 could be removed because of the fail-safe feature available in SN65HVD1782?

    2.For the part  TLP175A, it seems that the Ron 25-Ohm( typ.) / 50-Ohm(max)  will have a problem with the termination resistor.   I will replace it with VO1400AEF (please see the attached file). Is the load current 100 mA of the VO1400AEF enough?

    Please comment! Thank you.

    Best regards,

    Roy Hsu

  • In reply to Roy Hsu:

    Hi Roy,

    1. The failsafe network contains in your case R1801 and R1812 they pull up the the A and B BUS lines to insure that always a defined voltage is provided to the bus. You can find mor information (Page 10,11 and 12) here: 

    /cfs-file/__key/communityserver-discussions-components-files/138/5417.1106.slla036d.pdf

    2. 100 mA is enough current since the termination resistor is around 120 Ohms and the differential voltage is typical around 3 V which drives around 25 mA current when the BUS is is driven by the driver. I could not see any attachment maybe yo can upload it again if there are further questions. You can also search the E2E to find similar topics example: https://e2e.ti.com/support/applications/automotive/f/26/t/306385

    Kind regards 

    Dierk

  • In reply to Dierk Bronner:

    Hi Dierk,

    Thanks for the detailed reply!

    Best regards,

    Roy Hsu

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