Can ATmegaxXXU2 supply 3.3V to AT45DBxxx dataflash

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Chancy99
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Posted by Chancy99: Thu. Sep 27, 2012 - 06:24 PM
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I've been looking all over and can't really seem to find a definitive answer ... I would like to run an ATmega32U2 at 16MHz, which needs 5V. Also want to use an Atmel Dataflash, which needs 3.3V, meaning an additional 3.3V regulator or a couple of dropping diodes. Board space is very tight ....

Is it possible for an ATmega32U2/16U2 to supply enough current from the UCAP pin to power an Atmel Dataflash, like an AT45DB041D ?

I've read that it can supply up to 100mA, 50mA, 10mA. It also powers the D-/D+ pads, but there's no indication of how much is required for them. The Dataflash can take up to a max of about 17mA. If the supply is 10mA, there's no way, but for 50mA, yes it probably/possibly can ...

My eyes are bleary - I've probably missed something obvious in a datasheet somehwhere.

Dean 94TT
"Life is just one damn thing after another" Elbert Hubbard (1856 - 1915)

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AVR Microcontrollers, megaAVR and tinyAVR, ATmega32, ATmega32U2
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mnehpets
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Posted by mnehpets: Thu. Sep 27, 2012 - 09:50 PM
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This isn't a definitive answer, but section 26.2 of the datasheet characterises the Vreg output at up to 100mA. I read that as stating that the internal regulator is good for up to 100mA. There's no description of the current consumption of the USB port, but footnote in the atmega32u4 datasheet claims that it uses about 25mA from the Vreg output. Assuming the 32u2 is similar, that leaves you plenty for the flash.

- S

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chartman
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Posted by chartman: Fri. Sep 28, 2012 - 02:22 PM
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Be very aware..... These data flashes don't like their Vcc being lower than the drive device Vcc ( like most stuff)If there's any doubt, fit series resistors to SI,SO,SCK,/CS,/WP,/RESET to limit the current to <1mA

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Chancy99
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Posted by Chancy99: Fri. Sep 28, 2012 - 03:48 PM
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I thought they were 5V tolerant ?

Dean 94TT
"Life is just one damn thing after another" Elbert Hubbard (1856 - 1915)

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limpkin
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Posted by limpkin: Fri. Sep 28, 2012 - 07:02 PM
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Hi chancy,

I exactly did what you want to do...
Supply the avr with 5v, use the 3.3v to power the flash.
Add resistors in series for clk/mosi/cs and you're good to go.

Cheers

My electronic projects blog >> www.limpkin.fr

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Chancy99
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Posted by Chancy99: Fri. Oct 5, 2012 - 07:17 PM
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Why do you need resistors on CLK/MOSI/CS ? The inputs are 5V tolerant.

See page 47 of datasheet - "All inputs (SI, SCK, CS, WP, and RESET) are guaranteed by design to be 5V tolerant."

http://www.atmel.com/Images/doc8783.pdf

Dean 94TT
"Life is just one damn thing after another" Elbert Hubbard (1856 - 1915)

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chartman
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Posted by chartman: Sat. Oct 6, 2012 - 04:17 PM
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We had endless problems with the TSOP version. They went away when we fitted series resistors.The CPU ran at 4.3V and the flash at 3v3.I still believe it was a Vcc issue... OTOH it may have been something else. :(

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chartman
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Posted by chartman: Sat. Oct 6, 2012 - 04:18 PM
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We had endless problems with the TSOP version. They went away when we fitted series resistors.The CPU ran at 4.3V and the flash at 3v3.I still believe it was a Vcc issue... OTOH it may have been something else. :(

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