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    5v to 3.3v, around 70mA current at output.

    hi,

    my application is to convert 5v to 3.3v and 70mA output.
    i am looking for smd package.
    i found AMS1117 3.3v voltage regulatorhttps://www.aliexpress.com/item/10pc...8-a8c4c473449a

    i am confused in selected section shown in image.

    is this sentence want to say that it will work when there is voltage difference of 1v? it will not work if 4v is input and output is 3.3v

    Click image for larger version. 

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    thanks,
    vraj

    •   Alt11th September 2017, 15:24

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    Re: 5v to 3.3v, around 70mA current at output.

    Quote Originally Posted by Vraj View Post
    is this sentence want to say that it will work when there is voltage difference of 1v? it will not work if 4v is input and output is 3.3v
    Right. For 3.3V output, the input must be greater than 4.3V.


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    Re: 5v to 3.3v, around 70mA current at output.

    i found another one XC6206 662k.
    ams1117n was bigger in size.

    am i in correct direction?



    •   Alt12th September 2017, 13:58

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    Re: 5v to 3.3v, around 70mA current at output.

    Quote Originally Posted by Vraj View Post
    am i in correct direction?
    You will find very few regulators that have lower drop than 1V; the regulator needs some space to work. Perhaps you can get one with a 0.9V dropout but then they are rare.

    Anyway you will that 4V input cannot reliably produce 3.3V regulated output (most cases)


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    •   Alt12th September 2017, 15:01

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    Re: 5v to 3.3v, around 70mA current at output.

    Hi,

    but what´s the problem? You want to convert 5V to 3.3V.
    And the 1117 operates with input voltages > 4.3V
    5.0V > 4.3V. --> True. Everything is fine.

    Klaus



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    Re: 5v to 3.3v, around 70mA current at output.

    Hi,

    Why not use any of many preset or adjustable LDOs - maybe easily covering the 300 to 700-ish mV dropout headroom only?



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    Re: 5v to 3.3v, around 70mA current at output.

    Quote Originally Posted by KlausST View Post
    Hi,

    but what´s the problem? You want to convert 5V to 3.3V.
    And the 1117 operates with input voltages > 4.3V
    5.0V > 4.3V. --> True. Everything is fine.

    Klaus
    it was hard with another ics.
    i was using qfn 4*4 packge and 0402 packages. 1117 was looking bigger.
    XC6206 662k is available in sot23.
    amazing thing of XC6206 662k[/URL] is that, it is ceramic capacitor compatible.[URL="https://www.torexsemi.com/file/xc6206/XC6206.pdf"]
    may be they are used for smoothing i/p and o/p waves.
    my input is 5v from usb.

    i don't have oscilloscope, can you say that i should go with mentioned value of capacitor (as datasheet)?

    will capacitor rated with 10v will ok?

    - - - Updated - - -

    Quote Originally Posted by d123 View Post
    Hi,

    Why not use any of many preset or adjustable LDOs -
    present LDOs? e.g.?
    i need small smd package and cheaper one

    maybe easily covering the 300 to 700-ish mV dropout headroom only?
    means?



  8. #8
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    Re: 5v to 3.3v, around 70mA current at output.

    Hi,

    amazing thing of XC6206 662k[/URL] is that, it is ceramic capacitor compatible.
    I don't see this as drawback, I see it as benefit

    may be they are used for smoothing i/p and o/p waves.
    Every voltage regulator should have capacitors close at input and output to ensure stability.

    my input is 5v from usb.
    So your input voltage is not exactly 5.0V.
    Rather expect 4.2V ..... 5.5V (it is specified down to 4.5V, but I've seen many they go below this at the end of the cable)

    i don't have oscilloscope, can you say that i should go with mentioned value of capacitor (as datasheet)?
    Keep on the datasheet recommendations.

    will capacitor rated with 10v will ok?
    Yes.

    present LDOs? e.g.?
    Almost any true LDO with 3.3V output will do the job.
    There are hundreds of LDOs that can be used.

    I'd go to a distributor's or a manufacturer's web site selection guide to choos the right one.
    If you go to aliexpresss .... it's your way...

    Klaus


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    Re: 5v to 3.3v, around 70mA current at output.

    hi,

    My main MCU manufacturer has mentioned to add 4.7uF and 10nF capacitor to input 3.3v and ground.
    i think they mentioned to smooth i/p.

    my XC6206 662k is providing good o/p 3.3v with 1uF.

    i think, i should continue with 1uf and parallel with 10nF, avoiding 4.7uF.

    what's your opinion?

    i also meant impressive(amazing)

    thanks,
    vraj



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    Re: 5v to 3.3v, around 70mA current at output.

    Hi,

    you must not rely on any MCU manufacturer recommendation when you want stable XC6206 operation.

    Rely on the XC6206 datasheet.
    it clearely says to use 1uF ceramics each at input and output.
    Additionally it says:
    ...
    3. Please wire the input capacitor (C IN ) and the output capacitor (C L ) as close to the IC as possible.

    4. Capacitances of these capacitors (C IN , C L ) are decreased by the influences of bias voltage and ambient temperature. Care
    shall be taken for capacitor selection to ensure stability of phase compensation from the point of ESR influence.


    Klaus



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    Re: 5v to 3.3v, around 70mA current at output.

    hi,

    i think there is misunderstanding.
    i mean my main ic is MCU. MCU is rated 3.3v input.
    i need stable MCU operation.

    if small capacitors like 10nF used to smooth remaining high frequency, then should i use?

    thanks,
    vraj



    •   Alt13th September 2017, 09:38

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  12. #12
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    Re: 5v to 3.3v, around 70mA current at output.

    Hi,

    for stable MCU operation you need to follow the recommendations in the MCU datasheet.

    If they recommend to use 10nF capacitors then do so.
    But read carefully. Usually they recommend one capacitor very close at each VCC pin of the IC....this has nothing to do with the capacitors close to the voltage regulator.

    Klaus



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