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TPS7B7702-Q1: Need to double-confirm what is this spec mean?

Part Number: TPS7B7702-Q1

Tool/software:

Hi Team,

 We are using the TPS7B7702-Q1 now, and we find below spec seem to have some typo, need to double confirm with you.

From my side, I think we should limit the max value for this spec, it should mean the current sense current maximum should be 3.3mA. But from the spec, it seems the Minimum, so need to double confirm with you. And if you can explain its meaning, will be very grateful. Thank you.

Best Regards,

Kunyue

  • Hi Kunyue,

    During a fault condition the SENSEx output latches to one of the fault voltages (2.55V, 2.85V, or 3.2V), and depending on the size of the RSENSEx, more current could be needed to get the SENSEx voltage up to these fault voltages. If the spec was a maximum, the scenario where the fault voltages are not reached would be possible and the SENSEx output would not indicate a fault or indicate the wrong fault. 

    Regards,

    Nick

  • Hi Nick,

    Thank you so much for your quickly respond.

    So from your side, the below formula decide the maximum of Rsense? 

    For example, if the Iomax is 300mA, so the Rsense should be smaller than 198 X 2.4/ 300mA = 1.584 kohm. And the Vsense_stb max = 3.3V decide the minimum of Rsense, so the Rsense should be bigger than 3.3V / 3.3mA =1 kohm. So the Rsense recommend value is 1kohm ≤ Rsense ≤ 1.584kohm, right?

    Best Regards,

    Kunyue

  • Hi Kunyue,

    So from your side, the below formula decide the maximum of Rsense? 

    Yes that's correct. 

    For example, if the Iomax is 300mA, so the Rsense should be smaller than 198 X 2.4/ 300mA = 1.584 kohm.

    Yes.

    And the Vsense_stb max = 3.3V decide the minimum of Rsense, so the Rsense should be bigger than 3.3V / 3.3mA =1 kohm. So the Rsense recommend value is 1kohm ≤ Rsense ≤ 1.584kohm, right?

    This is not correct. There isn't a minimum RSENSE; if RSENSE is too small the VSENSE will be small and you lose resolution for the sensing measurement. This is the only limitation. I recommend sizing the RSENSE close to the maximum so that you get the most resolution while also not overlapping with the current limit fault. FYI, if you sized the RSENSE too large, the VSENSE will clamp at approximately 2.55V (same as the current limit) even when the device is not in current limit, so in this case you cannot distinguish the current limit fault, so this is why I recommend sizing the RSENSE slightly lower than the maximum so that there is guaranteed to be some margin. 

    Regards,

    Nick

  • Hi Nick,

    Understood, what I mean the smallest resistance is based on the spec of Isense minimum is 3.3mA. But I will not choose a resistance so small like that, I will follow what you said, to choose a resistance which is closer to the maximum value, thank you so much.

    Best Regards,

    Kunyue