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TPS65981: external power path over current protection

Stephen Zhu
Prodigy 30 points
Part Number: TPS65981

When TPS65981 External HV Power Switch is configured as a Sink With RSENSE, the Rsense is used to provide current measurement and current limit. If there's a short time big value inrush current, but I don't want to trigger this over current protection of TPS65981. Can I configure this feature in the "TPS6598x application Customization Tool"? For example add some delay time to ignore short time inrush current. I noticed that there's something like "external power path over-current timeout ", is that for this purpose? I have tried to configure the time to maximum value 81.92ms in the Tool software, but the over current still triggers.

 

Can this current limit feature be shut off completely?

  • 0
    TI__Genius 9710 points

    Hi Stephen,

    The External Power Path Over-Current Timeout field is used to set the time that an overcurrent condition must be present for an overcurrent event to occur (be triggered). This field should be able to be used to set a minimum overcurrent period duration like you want. 

    Can you send me your project file so I can check a few things? Please make sure the RSENSE value is configured correctly and that you are adjusting the settings for the correct power path. 

    How long of an overcurrent duration are you testing with? 

    Best,

    Alex

  • 0 in reply to Alex Liu
    Prodigy 30 points

    Hello Alex,

    Can I shut off this external path over current protection completely? Or can I set this timeout to much longer time? 

  • 0 in reply to Stephen Zhu
    TI__Genius 9710 points

    Hi Stephen,

    RSENSE when sinking is used for current measurement and reverse current protection, not overcurrent protection. As a sink, the PD controller does not do any overcurrent limiting or protection at all. If you see overcurrent trigger when the PD is sinking and the power shuts off, this is not the PD triggering this, but probably the far-end source device. The timeout setting is for overcurrent protection while sourcing only.

    If you do wish to use RSENSE for reverse current protection while sinking, please make sure to flip the connections to the two RSENSE pins. This is necessary to use RSENSE correctly when sinking only, disregard if RSENSE is configured with sourcing.

    Best,

    Alex

  • 0 in reply to Alex Liu
    Prodigy 30 points

    Hi Alex,

    On the datasheet  of TPS65981 page 39 "9.3.3.12 External HV Power Switch as a Sink With RSENSE", it's witten "Acting as a sink, the voltage between SENSEP (VBUS) and SENSEN (PP_EXT) is sensed to provide an accurate current measurement and initiate the current limiting feature of the external power path." Does this "current limiting feature" mean over current protection?

    Should I use this external path as describded in "9.3.3.13 External HV Power Switch as a Sink Without RSENSE"? Remove this sense resistor and tie the SENSEP  and SENSEN together. Because It's witten "This is used for...providing a supply voltage for a bus-powered device." We do use this VBUS power to power the entire product. If I remove this RSENSE resistor and short SENSEP and SENSEN, how should I make change in the "Application Customization Tool"? 

    We do have another TPS65981 as source on the other side of PD. Actually we have 2 identical TPS65981 boards on 2 products, TPS65981 is configured as "Dual Role Power". External power switch is configured as sink and Internal HV switch is configured as source. Depending on the situation, it automatically switch over between these 2 roles. I noticed that in the datasheet "9.3.3.9 Internal HV Power Switch Current Limit", it's written "The current through PP_HV to VBUS is current limited to ILIMPPHV (only when operating as a source) and is controlled automatically by the digital core. When the current exceeds ILIMPPHV, the current-limit circuit activates", I cannot find what's the value of "ILIMPPHV" in the datasheet. I think it's same with ILIMHV on page 14. 

    It's specific value is selected automatically based on the maximum current selected in the Cus Tool, if maximum current is 3A, the ILIMHV value will be setting 9 or somethink like this. Is my understanding right?

  • 0 in reply to Stephen Zhu
    TI__Genius 9710 points

    Hi Stephen,

    I consulted our systems engineers and we confirmed that the datasheet is not correct in saying the PD controller does current limiting on PP_EXT when sinking. We do not do any current limiting on any power path when sinking. This is the responsibility of the source device.

    You can still use RSENSE for reverse current protection. However, if you do not wish to use RSENSE on PP_EXT path, you can tie SENSEP and SENSEN together as the datasheet states. I do not believe any configuration changes are required.

    ILIMPPHV for the internal PPHV path is determined by the "Max Current" field of the active PDO configured in the TX Source Caps register. Our firmware internally configures the ILIMPPHV current limit based on the active source PDO. Your assumption is correct.

    Best,

    Alex