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TPS25921L: Reverse Current Protection

Satish Acharya
Prodigy 230 points
Part Number: TPS25921L
Other Parts Discussed in Thread: LM66100

Hello,

My application needs all the standard circuit protection and I plan to use TPS25921L eFuse part right at the 5V power inlet into the system. Typical operating voltage and current conditions are 5V and 400mA. There is a large 2200uF (or higher) capacitor load after eFuse for which charging current will be limited to around 600mA. I have not performed all the calculations for TPS25921L yet to check if this can be achieved. There are a couple of 3.3V/3.5V LDOs further downstream. The large cap is needed to prevent interruption of a write in the MCU with integrated flash in case of power loss.

The application also needs reverse polarity protection on the input and reverse current protection from the large 2200uF cap. To keep cost low, I plan to use a low-drop Schottky diode on the eFuse input for reverse polarity protection. My application does not allow me to put the Schottky diode on the Ground path.

Question is whether the Schottky diode on the input of eFuse also provides reverse current protection from the cap and if the TPS25921L part is safe to use in this configuration.

I'd appreciate your thoughts and any potential gotchas or issues to keep in mind.

Thanks,

Satish

  • 0
    TI__Guru 57737 points

    HI Satish,

    Yes, a diode in the series path with TPS25921L will protect your system from Reverse Polarity Protection and helps in  Reverse Current Blocking.

    For reverse current to flow from Output capacitance the voltage at Vin has to be lower than the voltage at Vout. In this condition, the diode will be reverse biased and will block reverse current flowing from Vout to Vin.

    You can consider using TPS25942 or TPS25944 family of devices instead of using a diode in series with TPS25921L as it protects your system by Reverse Current Blocking and 1-µs Reverse Voltage Shutoff.

  • 0 in reply to Praveen GD
    Prodigy 230 points

    Thank you Praveen for the prompt response.

    I considered TPS25942 or TPS25944 but they don't have reverse voltage protection. So, either I need to pick a more expensive part or insert a Schottky diode. I was thinking of the latter.

    Regards,

    Satish

  • 0 in reply to Satish Acharya
    TI__Guru 57737 points

    Hi Satish,

    In case you want reverse polarity protection, I think the better way than using a diode is using a PFET in series (ahead of TPS25921L) with its Gate connected to GND. 

  • 0 in reply to Praveen GD
    Prodigy 230 points

    Hi Praveen,

    Yes, I could use a PFET for reverse polarity but reverse current protection will now require additional FET with a comparator. Alternatively, one could use an ideal diode controller (e.g. LM66100) which can do both reverse polarity as well as reverse current protection.

    Or, go with TPS25942 or TPS25944 which has reverse current protection and then add a PFET in front for reverse polarity.

    Any other ideas?

    Thanks,

    Satish

  • 0 in reply to Satish Acharya
    TI__Guru 57737 points

    Hi Satish,

    You are absolutely Right!. The two options you mentioned are the best we can come out with.