Can someone help me decode this spec sheet?

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#1
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I have this 5V to 3.3V regulator: http://ww1.microchip.com/downloads/en/DeviceDoc/22056b.pdf

I'm trying to figure out what the minimum Vin is before its 3.3V output isn't reliable anymore.

I see Vin = Vout(max) + Vdropout(max) which I guess would be 6 + 0.35 = 6.35 volts in which doesn't seem correct.

I'm just trying to go from 5V to 3.3V and would like to know how much head room about 3.3V I have to work with on the voltage input side.

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Shirley, paragraph 5.1 shows the exact example of what you want to do.

Looking at Fig 2.8, lower currents involve lower dropouts. Other curves show the temp and current.

David.

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paragraph 5.1 talks about 2.5V out instead of 3.3V. It's not clear to me how they get their Vin numbers in that example - it just isn't shown.

Figure 2.8 shows the dropout voltage for 3.3V output ranges from 0.21V to 0.28V at full current output.

Does that mean I should have at least 3.3 + 0.28 = 3.58 Volts in?

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The way I read this data sheet is that Vdropout max == 350mv. So, max vout of 3.3V is 3.333V.(1%) So 3.333V plus 350mv is 3.683V needed at the input to the device and all will be well. (Vin)

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I think that's right. My 5V supply to this chip shouldn't really have any issues then.

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Nope. If you give it 5V +-5%, worst case it will be 4.75V. Way lots of headroom.