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TPS7A8300: Reverse current protection for an LDO ??

Madhu Wesly
Intellectual 280 points
Part Number: TPS7A8300
Other Parts Discussed in Thread: TPS7A83A

Hi, 

I want to use TPS7A8300 in my design. My application is Battery powered, so there will be the minimum voltage of even 2V(or Less) at Vin pin of the LDO.

Since this LDO does not have Reverse current protection, will there be any issue if I do not provide Reverse current protection externally???

One more doubt is will there be any chance of going VOUT higher than VIN in the above application?? This LDO doesn't Boost at any case right??

Thanks in advance.

  • 0
    TI__Guru 55940 points
    Hi Madhu,

    You only need to add reverse current protection if Vout may exceed Vin in your application. You are correct that the LDOs do not boost the voltage; however, there are a few ways that Vout may exceed Vin in an application.

    In some multi-rail applications the output of the LDO could be unintentionally biased above its set voltage. Since most LDOs do not have a way to sink current, it is up to the LDO's load to pull the output voltage back within regulation. If Vout is biased above Vin, reverse current can flow.

    More commonly, if the input of the LDO were to collapse at a faster rate than the LDO output capacitors can be discharged, Vout would exceed Vin and reverse current can flow.

    Please consider using TPS7A83A for your application as it is the next generation of TPS7A8300. TPS7A83A is pin-to-pin and is more user friendly as it does not have any sequencing requirements.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Intellectual 280 points

    Thanks for the reply.

    As it is told by you and given in Datasheet: 

    Conditions, where excessive reverse current can occur, are outlined in this section, all of which can exceed the absolute maximum rating of VOUT > VIN + 0.3 V:

    • If the device has a large COUT and the input supply collapses quickly with little or no load current.

    To avoid it:

    Is large COUT means in-terms of Size or Value?? If it is the size is it okay to keep 0805 at COUT and 1206 at CIN or 1206 at both CIN and COUT??

     

    Or can you suggest the equivalent part number with Reverse current protection?? 

     

    Thanks in advance.

  • 0 in reply to Madhu Wesly
    TI__Guru 55940 points

    Hi Madhu,

    It is the capacitor value not the package size that matters.  The more capacitance on the output rail, the more energy is stored on the output that could flow backwards through the LDO if Vin were to drop below Vout.  

    It is important to note that TPS7A83A does have an active pulldown on the output when EN is driven to logic low.  The active discharge will provide a safe discharge path from the output capacitors to GND if you were to disable the LDO; therefore, it is only if the output rail suddenly collapses while the LDO is still enabled that could potentially cause reverse current.  As your Vin is a battery, this case is probably unlikely in your application.

    We do not have a high current LDO with a built in reverse current protection that is not qualified to a higher grade such as automotive devices.  If you believe that reverse current could occur in your application, please consider adding a diode in between OUT and IN.  This diode will provide a robust path for reverse current should Vout exceed Vin.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Intellectual 280 points
    Hi Ryan Eslinger,

    Thanks for the reply.

    Previously I used the following LDO on my board -
    www.st.com/.../l6932.pdf - With this there is no problem till now, It is working Okay though there is no Reverse current protection diode internally or externally.

    So, Will this new LDO TPS7A83A require ?

    Thanks in advance.
  • 0 in reply to Madhu Wesly
    TI__Guru 55940 points
    Hi Madhu,

    You only need reverse current protection (either built into the LDO or externally provided) if Vout is expected to exceed Vin. It does not sound like your application will have this occur from the details that you have provided. As such you would not require any reverse current protection.

    Very Respectfully,
    Ryan