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LP3855-ADJ: Recommended output voltage

ArTzy
Genius 15899 points
Part Number: LP3855-ADJ

Hi Experts,

Good day.

I want to clarify the recommended output voltage of this LDO device, LP3855-ADJ.

TI website shows 6.6Vout max but I couldn't find it from its datasheet. We are actually looking for an LDO device that converts down 6.6Vin voltage to 6.0Vout (with voltage drop of 500mV).

I just have to make sure that this device would work and follows its recommended spec's, not the absolute reading.

Also, please have as clarify about its Electrical Characteristic operations. It was specified there that the Vin is 1V higher than Vout (at the top notes); however, the dropout voltage there (Vin-Vout) has maximum value of 435mV. I wanted to be sure also, what's the recommended dropout range as this device is tagged as ultra low LDO.

Hoping for your guidance.

Thank you.

Regards,
Archie A.

  • +1
    TI__Mastermind 36135 points

    Hi Archie,

    Maximum Vin is 7V but the datasheet does specify a 7.5V survival input voltage rating.  Use 7V maximum for steady state operation.

    Maximum Vout is based on the dropout requirement or headroom you need for performance.  "Dropout" specifications are always given in LDO datasheets for steady state operation.  So with maximum load, you will enter dropout (worst case) with less than 435mV of headroom.  Keep in mind that you need less headroom than 435mV if your load current is less than 1.5A. 

    Because dropout is considered a steady state or DC parameter, transient performance metrics require more headroom than dropout values.  Common values for transient performance is 1V of headroom.  More modern LDO's are pushing this 1V down to 100's of mV, and high current LDO's also typically require less than 1V of headroom for transient performance, so you will want to read the datasheet for this metric for each LDO.

    If you only need DC performance and do not expect significant transients in the system, then 435mV is sufficient.  If you anticipate that the LDO will see transient conditions you may want more headroom.  While the datasheet lists 1V (which is common practice) you can use an EVM with your actual load, and capture measurements to determine if the LDO will meet your system needs.  In cases where your load is less than 1.5A, you may be completely fine with 500mV of headroom even with transient loading.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    TI__Genius 15899 points

    Hello Stephen,

    Thanks for these!

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 36135 points

    No problem Archie, let us know if you need anything else.

    Thanks,

    Stephen