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Original question:

Back feeding TLV62130

TPS62230: Preventing backfeeding of TPS62237

Andrew Mowry
Prodigy 90 points
Part Number: TPS62230

I'm sorry for asking this because I know it's a common question, but I just want to be sure. I want to prevent backfeeding the TPS62237 buck converter from a secondary power supply (I have 5 V reduced by the buck to 3.3 and a NiMH battery increased by a boost to 3.3 V). I'm okay with putting a Schottky diode on the 5 V input to the buck converter, but is this sufficient protection to prevent current leakage? In other words, is there also a path to GND or other pins when I backfeed the converter, or do I only need to worry about the path to the input?

  • 0
    TI__Genius 16530 points

    Hello Andrew,

    Thank you for reaching out.

    Can you please specify the mode of operation? For DCS-Control, if the output goes above the setpoint, power save mode is entered.  This is perfectly fine as long as the abs max rating of the output is not exceeded. The problem comes with the PWM mode and it also depends upon the amount of extra output voltage that you are back feeding.

    And what would be the maximum output voltage increment on TPS62230?

    Andrew Mowry said:
    I'm okay with putting a Schottky diode on the 5 V input to the buck converter, but is this sufficient protection to prevent current leakage?

    Generally the path will be through input side, so if you use a Schottky diode the it acts like a extra protection and there should not be any problem.

    Thank you & regards,

    Moheddin.

  • 0 in reply to Moheddin Pasha Shaik
    Prodigy 90 points

    Thanks! I think I understand, but just to be 100% sure:

    If I have a Schottky on the input side of the TPS62230 and there is no voltage applied to the input (the 5V source is disconnected), and I apply 3.3 V to the output, the TPS62230 won't be harmed and there won't be any significant current lost through the device (I'm okay with a few hundred uA lost). 

  • 0 in reply to Andrew Mowry
    TI__Mastermind 33891 points

    Hi Andrew, 

    Kindly allow me to respond to your queries, as Moheddin is out of the office.

    If the output rail is externally biased with 3.3V while the 5V supply is disconnected, TPS62230 can potentially turn on because VIN is over UVLO (VIN = 3.3V - Schottky diode forward voltage). It might not cause any harm to the IC at PFM mode (MODE pin = Low) because it will just stop switching if Vout is slightly over the voltage regulation. At PWM mode (MODE pin = High), the IC will keep switching even if the output voltage is above the regulation level, which can cause a high voltage ringing on the VIN rail due to reverse current (output capacitor charge is discharged to VIN rail).

    It is still best adding a load switch between the buck converter output and the 3.3V rail to prevent reverse current. Please see the app note link below for details.

    https://www.ti.com/lit/an/slva730/slva730.pdf?ts=1687851791984&ref_url=https%253A%252F%252Fwww.google.com%252F

    Best regards,

    Excel

  • 0 in reply to Excel Regidor
    Prodigy 90 points

    Okay, thanks for your help. Just to clarify, I'm actually using the TPS62237 (the form would only let me choose the TPS62230), so the regulation is 3.3V.

    I do have the MODE pin tied low so it would be in PFM mode, but it sounds like it would still be safest to add a load switch as you described.

  • +1 in reply to Andrew Mowry
    TI__Genius 16530 points

    Hello Andrew,

    There might not be any problem if you are using the device in PFM mode but you can use a load switch for extra protection.

    If you don't have any further questions can you please close the thread by clicking on resolved.

    Thank you & regards,

    Moheddin,