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UC1825B-SP: Vref usage for other circuits

Susan Miracle
Prodigy 70 points
Part Number: UC1825B-SP
Other Parts Discussed in Thread: UC1825

Hi,

I am looking at a design that uses the Vref to power other circuits on the card.  It is used to power an LDO and as the collector voltage of a couple of transistors.  The data sheet says that Vref will supply at min. 15mA.  This device is being used in a military application and so, my first question is has this part been built with MIL-STD-1547 compliance?  If not, then this 15mA will need to be derated in accordance with MIL-STD-1547.  I am also wondering, if Vref has been designed to be 0 volts, during under voltage operation or is this voltage basically uncontrolled during under voltage operation?  Also, there seems to be 1.1uF capacitance across it to ground.  The data sheet states there should be 0.1uF.  Is there a performance impact to increasing the capacitance?  Do you recommend using Vref to power other circuits?  What is the intended use for Vref.  Is it intended to be used with the UC1825 only?

Thanks!

Susan

  • 0
    TI__Mastermind 25295 points

    Hey Susan,

    Please see the SMD for the product:
    https://landandmaritimeapps.dla.mil/Downloads/MilSpec/Smd/87681.pdf

    In Section 2.1 it outlines the standards used.
    We follow the standards for QMLV process flow as well as the standards for RHA for radiation hardened parts..

    As far as the VREF is concerned, it is used internal to the part as a intermediate power rail that comes out of an internal LDO.
    Its main use in the system is to be used through divided down resistors as a voltage reference for the error amplifier.
    It is not tested under UVLO conditions.

    You state there is 1.1 uF to ground, could you please note the figure?
    I would not expect a performance increase in terms of voltage accuracy, but it may help is there is a sudden current draw.

    Thanks,
    Daniel