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THVD4431: Power supply capability

Akash S
Intellectual 790 points
Part Number: THVD4431

Hi,

The maximum short circuit current in RS485 mode is mentioned as 250mA. 

Is there any over-current protection in the chip so that the it can cut off below the short circuit current or should the power supply be rated to handle this current.

If we implement an external over current protection, can we set it at 100mA such that it does not affect the normal operation?

  • 0
    Guru 316440 points

    The short-circuit output current specification describes how the device behaves. If there were a current limiter, this specification would be lower.

    You can use any external protection circuit, as long as the voltage does not drop for normal currents (up to 50 mA).

  • 0
    TI__Guru 52012 points

    Hi Akash,

    As Clemens mentioned the 250mA is how the device reacts. You can add a current limiter as long as it has very little impact on circuit - generally 60mA is the recommended output current of RS-485 - but having a limit of 100mA should give some margin and work okay. 

    Please let me know if you have any other questions!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Intellectual 790 points

    Hi Parker,

    Thanks for the response.

    Can you pls suggest a current limiting circuit to restrict the current to 100mA

  • 0 in reply to Akash S
    TI__Guru 52012 points

    Hi Akash,

    1. If you do limit current - do know that you will be in compliance with RS-485 and failure can occur when current is limited; RS-485 requires the 250mA short circuit maximum + other current lost through device. Essentially - for compliance your power tree cannot be restricted

    2. I don't have a good specific suggestion - it would be easiest to do it through the power tree - I'd honestly ask a question for a current limiting LDO over in our Power Management forum  (https://e2e.ti.com/support/power-management-group/) as that may be the best bet as they are more familiar with these types of applications - largely this is not something that is done in RS-485 because it makes your system non RS-485 compliant. Honestly I wouldn't current limit; I'd redo the power tree to allow for the max current in RS-485 for compliance - as non-compliance removes a lot of benefit from RS-485 apps. But if you are set on doing this - please ask a question in our power management forum because they will be the most up to date.

    Best,

    Parker Dodson