## Can someone help me decode this spec sheet?

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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.

Total votes: 0

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.

Total votes: 0

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?

Total votes: 0

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)

Total votes: 0

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

Total votes: 0

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