blast from past

One thing I don't miss are the tag strips ;) Would've glued a bit of blank PCB behind the panel and buzzed a pattern with diamond bit for those few components. No screws in front panel then ;')

Bet you're glad to be moving those new V220 whatsits out the door?

Grant.

Do I see three tantalums on the bottom right? Oh-oh ... :-)

Your replacement is?

Yes. LM1117's like tantalums on their outputs; the ESR is just right, and will hold up at -20C. They are all 22u, 10v, 11 cents each, on the outputs of 3.3, 2.5, and 1.25 volt regulators. That should be safe.

Why make rules if you can't break them once in a while?

The 1.25 is FPGA core voltage; that's an LM1117 with its adj pin grounded. The 2.5 is FPGA VCCaux, another LM1117 with its adj pin tied to the 1.25 rail. I would happily show the programming resistor values, except there aren't any.

John

Well, if you have good experience with the LM1117 maybe it works. I just don't trust LDOs anymore, too much grief. Only one was my own design and only because the client absolutely insisted on a particular LDO to be used. Then, sure enough ... *PHOOF* ... *POP*

Ceramics. Cheap. If an LDO is used (I always recommend not to do that) and it requires a particular ESR range you can place resistors in series. At least then you can be sure what the ESR is.

Yep, 1.2V is not exactly low drop-out. ...Jim Thompson

The 1117 is basically an LM317 architecture with a little less dropout. The final pass transistor is an NPN, so the open-loop output impedance is relatively low. They are rugged, cheap, and stable if you put a tantalum or aluminum on their output.

I use them as power amps, too, driving the adj pin with an opamp.

John

At least they state a range from 0.3ohms to 22ohms for this one instead of some obscure graph. I'd still prefer ceramics plus resistor but that's more real estate which in your case often matters a lot.

I have done that with the LM317, using it as a modulator. It doesn't get much cheaper than that because the transmit stage needed a regulator anyhow. So it was essentially a free modulator.

All these problems just to save a package pin, or do the design right in the first place. ...Jim Thompson

Ceramics are pretty limited. I've tried eliminating our Tantalums, but have only managed to find replacements for about half of them (by part number).

What kind of limitations did you encounter? Nowadays you can get tens of uF in X7R at really low cost. Of course, one has to stay away from very large sizes in portable equipment or anything that can vibrate.

Must be SMT. The problematic ones were those above 22uF (220uF is a bitch),

Which dielectric did you find to give +80/-20% ?

Z5U is often rated as such.

The dismal ratings give way to equally dismal temperature and voltage = coefficients, in the opposite direction (something like -80% at full = rated voltage or temperature).

Tim

--=20 Deep Friar: a very philosophical monk. Website:

And you get thermal limiting and current limiting for free.

John

What did you use for the labels?

Ed

h),

Y5V

Hmmm, he said "Blast from the past" ;-)