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ISOW7842: Input/Output voltage correlation

Patrick Denz
Prodigy 10 points
Part Number: ISOW7842
Other Parts Discussed in Thread: LP2985A, , ISOW7742

Hello!

I'm supplying the LDO LP2985A with the output of a ISOW7842 (3.3V primary driven). The output can be as low as 3.13V (for currents up to 30mA) and the dropout voltage of the LDO can be up to 148mV for currents up to 10mA.

So my input voltage to the LDO can be lower then 3V in very worst case conditions at least theoretically. Meaning that the LDO fully turns on. I want to avoid that and guarantee an input voltage higher than 3V at any time.

The ISOW7842 has a very broad input voltage range with 3.3V +-10%. I'm feeding 3.18V minimum to it and am therefore far above the -10% limit.

So my question is, does the input voltage of the ISOW7842 correlate to it's output voltage?

Meaning that when I have at least 3.18V at the input, I must not count with the minimum output voltage of 3.13V?

Thanks and best regards!

Patrick

  • 0
    TI__Guru 55405 points

    Hi Patrick,

    Thank you for reaching out and for sharing details related to your question.

    The output voltage variation of ISOW7842 is due to multiple factors - input voltage, temperature and part-to-part manufacturing differences. When a device is subjected with worst-case values of these parameters then it is going to see the worst-case output voltage. Hence, the input voltage alone isn't deciding when the output voltage is hitting 3.13V.

    If possible, please maintain the input supply to as close as possible to 3.3V so that the output regulation also stays close to the typical value. If the temperature range at which device is operated is narrower than datasheet quoted range, then the output variation can be minimal.

    Let me know if this answers your questions.
    I would also like to mention that ISOW7842 is our first-generation device, we recommend you to consider our second-generation device ISOW7742 that offers significantly higher overall performance. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 10 points

    Thanks for your answer!

    Okay so I'm not utilizing the complete temperature range up to 125°C.

    Can you tell what minimum voltage to expect for narrower temperature ranges?

    Regards,

    Patrick

  • 0 in reply to Patrick Denz
    TI__Mastermind 24245 points

    Hello Patrick, 

    As Koti stated previously, the listed Min and Max values for VOL take into account the process voltage and temperature variations. For a narrower temperature range, you can expect less variation. 

    Koteshwar Rao said:
    If the temperature range at which device is operated is narrower than datasheet quoted range, then the output variation can be minimal.

    Unfortunately, we will not be able to quantify how much variation outside of the rated min and max values. 

    Best,
    Andrew