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TPS7A47: Reverse Current Protection

Sadanori Kato
Guru 36540 points
Part Number: TPS7A47
Other Parts Discussed in Thread: TPS7A85,

Hi,

If the input voltage falls(VIN = 0V), the output voltage becomes higher than the input voltage(VIN < VOUT) for a few seconds.
So, does the reverse current flow from the output side to the input side ?
* e.g. : VIN = 0V, VOUT = 1V
In addition, could you please tell me how to protect if the reverse current flows to the input side ?

Best regards,
Kato

  • 0
    TI__Guru 55940 points

    Hi Kato,

    TPS7A47 does not have any dedicated reverse current protection or blocking; therefore, when Vout exceeds Vin, there is the potential for reverse current to flow and potentially damage the LDO.  If this is expected in your application, external protection should be added.  The most common method is to add a Schottky diode in parallel with the LDO to provide a robust reverse current path.  

    If devices upstream from the LDO need protected, a diode placed in series before the LDO input capacitor will block the reverse current from reaching the upstream supply to the LDO.  If a diode is placed in series, be sure to account for the diode drop to ensure that you still have adequate headroom (Vin - Vout) for the LDO to maintain regulation.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Guru 36540 points

    Hi Ryan-san,

    Thank you for the explanation.

    I found the following thread regarding the AbsMax voltage between OUT pin and IN pin.
    So, if the voltage between OUT pin and IN pin is -0.4 to 2V, is my understanding correct that TPS7A47 doesn't damage ?

    TPS7A47: SENSE, OUT pin Absolute maximum ratings
    https://e2e.ti.com/support/power_management/linear_regulators/f/321/t/656954

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru 55940 points

    Hi Kato-san,

    TPS7A47 was designed, tested, and characterized to operate within the Recommend Operating Conditions.  The Absolute Maximum Ratings are stress ratings only.  Exposure beyond the Absolute Maximum Ratings has an extremely high risk of damaging the LDO; however, prolonged exposure beyond the Recommended Operating Conditions may degrade the device reliability.  

    If your application has the possibility of reverse current (Vout exceeds Vin), it is recommended to take external protection precautions as described above. 

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Guru 36540 points

    Hi Ryan-san,

    Thank you for the information.

    I understood.

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    Guru 36540 points

    Hi Ryan-san,

    I just got an additional question from our customer, so could you please tell me that reason why there isn't mentioned in the data sheet that TPS7A47 doesn't provide the reverse current protection feature ?
    TPS7A85 also doesn't provide one, but there is mentioned about the workaround on page 31 of TPS7A85 data sheet.

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru 55940 points
    Hi Kato-san,

    Unless explicitly stated that an LDO has a dedicated reverse current protection it should be assumed that there is no reverse current protection. The majority of LDOs do not have dedicated internal reverse current protection. Most datasheets without reverse current protection do not include a section stating that it is not included.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Guru 36540 points

    Hi Ryan-san,

    Thank you for the explanation.

    I understood.

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    Guru 36540 points

    Hi Ryan-san,

    I found that the AbsMax for OUT, NR and SENSE/FB pins is definitely mentioned in TPS7A47-Q1 data sheet as below, so would this mention be also applied to TPS7A47(the non-Q1 part) ?
    If yes, not only our customer but also I believe that TPS7A47 data sheet should be revised.
    Could you please tell me your opinion about it ?

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru 55940 points
    Hi Kato-san,

    You are correct that it has become best practice to state the Absolute Maximum voltage rating for Vout on LDOs without a dedicated reverse current protection with reference to Vin. I have noted for this to occur in the next datasheet revision for TPS7A47.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Guru 36540 points

    Hi Ryan-san,

    Thank you for the comment.

    I understood.

    Best regards,
    Kato