Voltage divider for VREF --- what value resistors?

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futz

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I want to use two equal value resistors for a voltage divider to get a 2.5V VREF+ from my 5V VDD. What value resistors are recommended for this?
 
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Use a TL431, else it needs to be about 250ohms impedance. So a pair of 247ohm resistors would do the trick.
I've done it on the Junebug with VR2 and a 10uf cap in CON4
 
blueroomelectronics said:
Use a TL431, else it needs to be about 250ohms impedance. So a pair of 247ohm resistors would do the trick.
Click to expand...
Cool. I don't have a TL431. Should order some in my next order because I keep running into this problem. I'll do it with resistors for now. Nearest resistors I have to 247hm: is 330hm:. Close enough? Probably fine, right? There's virtually no current draw on it, I would think.
 
It's in the 18F1320 datasheet, the A/D actually sinks and sources the VREF+ pin. A cap should stop that. The TL431 is pretty handy too.
 
blueroomelectronics said:
It's in the 18F1320 datasheet, the A/D actually sinks and sources the VREF+ pin. A cap should stop that.
Click to expand...
OK, here's where my electronics ignorance shows. What does that mean?

The datasheet recommends 250hm: max impedance for VREF+ source. (whatever that means ).
 
Oh ya, Bill, your blog here won't allow me to post a comment. I was going to say (in re: your Lab-Easy comment) that DipMicro is liquidating Lab-Easy products. Poor sales? Promo? Guess I should buy some while it's cheap...
 
futz said:
Oh ya, Bill, your blog here won't allow me to post a comment. I was going to say (in re: your Lab-Easy comment) that DipMicro is liquidating Lab-Easy products. Poor sales? Promo? Guess I should buy some while it's cheap...
Click to expand...

Yes get some, they are cheaper than cost.

Dunno why you can't post a comment, Pommie did.
 
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