output voltage tolerance calculation ADP1762-ADJ

Hello,

I would like use ADP1762 adjustable LDO.

My application needs power supply +0.975V +-0.025V (≙ accuracy 2.56%) at 1.7A.
Supply voltage tolerance sourced to LDO input is +1.8V +-0.1V.
Ambient temperature definition from 0°C to +40°C.

How I have to calculate LDO output voltage tolerance?
Is it possible to achieve requirement with ADP1762 adjustable device?
Do I need Radj with less then 1% tolererance?

My worst case tolerance calculation resulting in more then 4% exclusive Radj tolerance.

It seems to be unusual much.

Best regards
Andreas

  • 0
    •  Analog Employees 
    on Nov 29, 2017 4:26 PM

    Hi,

    Output voltage accuracy of ADP1762-ADJ is affected by the adjust resistor (RADJ), adjust current (IADJ) and the ADJ gain factor (AD).

    VOUT = RADJ x IADJ x AD

    At worst case conditions, VOUT accuracy is computed as:

    You are right that it would reach approximately ±4.0% worst case tolerance and this is typical in ADJ models because of different sources of errors introduced to the LDO.

    I suggest you apply an output voltage margining to ADP1762-ADJ and set your VOUT nearer to 0.975V to achieve your desired accuracy for your application. You can refer to this article to guide you in designing your voltage margining circuit: “Voltage Margining Made Easy”

    (http://cds.linear.com/docs/en/lt-journal/LTC2920-1_1203_Mag.pdf).

     

     

    Regards,

    Errgy

  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:59 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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    EZ Admin