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TPS25810-Q1: Rref=10Ω

Kuramochi Tadahiko
Guru 28715 points
Part Number: TPS25810-Q1
Other Parts Discussed in Thread: TPS25810A-Q1, TPS25810,

Hi,

Ios is specified on Rref=10Ω as below.

Though Rref must be set to 10kΩ basically, what case is this specification supposed?

Best Regards,

Kuramochi

  • 0
    TI__Expert 8980 points
    Hi, Kuramochi-San,

    Rref must be 100kohm not 10Kohm. But if you set it lower, it will influence the current limit point. As spec shows, if you set it to 10ohm, max current limit will be 7A.

    Anyway, for normal use, just set ref to 100kohm to get normal current limit.

    Regards,
    Bob
  • 0 in reply to Bob Ma
    Guru 28715 points

    Bob-san,

    Thank you for your answer.

    Does it mean that Rref other than 100kΩ is allowed?

    On the datasheet, 100kΩ is designated as below.

    Best Regards,

    Kuramochi

  • 0 in reply to Kuramochi Tadahiko
    TI__Expert 8980 points
    Kuramochi-San,

    We don't recommend to use Ref other than 100Kohm. This resistor will influence the current limit point. And all our tests are based on 100K resistor, so we just guarantee the performance when ref=100kohm.

    Regards,
    Bob
  • 0 in reply to Bob Ma
    Guru 28715 points
    Bob-san,

    Thank you for your information.
    I understood.

    Why is Rref=10Ω condition specified on the datasheet?

    Best Regards,
    Kuramochi
  • 0 in reply to Kuramochi Tadahiko
    TI__Expert 8980 points
    Kuramochi-San,

    It's just a information for customer reference? Do you really want use the limited current be very high to 7A? Or are you just investigating this part?

    Regards,
    Bob
  • 0 in reply to Bob Ma
    Guru 28715 points
    Bob-san,

    Thank you for your answer.

    The customer want to use high current limit because another part has current limit function.

    Best Regards,
    Kuramochi
  • 0 in reply to Kuramochi Tadahiko
    Guru 28715 points
    Bob-san,

    I have additional questions.

    >It's just a information for customer reference.

    Does it mean that this characteristic was specified because a customer required this information?
    If yes, do you know why the customer was required this spec?

    And, if Rref is set 10Ω, what characteristics is affected by except for current limit value?

    Best Regards,
    Kuramochi
  • 0 in reply to Kuramochi Tadahiko
    TI__Expert 8980 points

    Kuramochi-San,

    If customer want to use another part to limit current and want TPS25810 have higher current limit level, can you check with customer whether TPS25810A-Q1 meet their requirement. This part's current limit level is always 3.4A no matter how much CC broadcast is.

    As we didn't validate the part's function at Rref=10ohm, so I prefer TPS25810A if it works.

    If this can't meet customer's requirement, I will check with designer to see if 10ohm Rref can be used.

    Regards,
    Bob

  • 0 in reply to Bob Ma
    Guru 28715 points
    Bob-san,

    Thank you for your support.

    They prefer to set Rref=10Ω than using TPS25810"A"-Q1 because they are already proceeding TPS25810-Q1 evaluation.
    Could you please ask the designer?

    Best Regards,
    Kuramocchi
  • 0 in reply to Kuramochi Tadahiko
    TI__Expert 8980 points
    Hi, Kuramochi-San,

    Sorry for letting you waiting so long time, I just get reply from designer yesterday night. Below is his reply, I think it's very clear.

    The TPS25810 does not have a programmable current limit. The Rref resistor is used to create the reference current for the device. This reference current is used for both the current limit AND the Type-C CC sourcing current outputs. Setting Rref to 10 ohms will definitely cause the part to BE UNABLE to support Type-C operation.

    You can see the recommended range of Rref in the Recommended Operating Conditions = 99 to 101 kohms. This is needed to meet both the current limit and Type-C specs.

    I am unsure if the customer wants to increase the current limit so he can run greater current through the device, but if he is, the same Recommended Operating Conditions table also states the maximum rated current is 3A. Going beyond this can reduce device lifetime.

    The spec line item in the OUT-Current Limit is just to let the customer know what happens if the REF pin becomes shorted. UL has a requirement that two point failures are still safe. In this case the two point failure is the Ref resistor is shorted and the OUT is shorted. The 7A max meets the UL limit.

    Regards,
    Bob