fixed negative LDOs

I've been using a bunch of TPS7A30's recently, but they're not fixed unless you want -Vref (-1.2V). Two resistors and a cap isn't so bad.

Life is hell when you're off in a dusty corner of the marketplace.

This is a mockup.

I need to squeeze roughly 55 parts onto that board, with keepouts on top and bottom edges. I'm agonizing over every part.

There's a simple solution to that, allowing using ordinary positive switcher ICs. A buck to boost, and a boost to buck, haha. We've written this up for AoE x-Chapters. I'll post it when I get home.

Lovely little RA Lemo there $$. If you go lots of layers, buried vias and mount parts both sides...

--sp

AKA anything that isn't running off a digital supply..

Yep, I do that a lot. For serious crowding, leave off the part-designator labels. Add right angle daughter boards, parts both sides, no labels. 3D.

How much current do you actually need from the negative rail? LM27761As are nice (with enough input filtering).

-- john, KE5FX

D'oh, never mind the 'A', just plain LM27761.

-- john, KE5FX

It sucks to be you. Tell the customer it's gotta be bigger, or do less, or it'll take more time. And, charge by the hour.

Yeah, analog circuits.

Luckily I don't need a charge pump. I have + and - 6 volts available to my box, and just need to regulate a few supplies down: +3.3, +2.5,

-2.5. It's refreshing, these days, to have a board with only 5 power rails.

On Fri, 14 Apr 2017 10:51:34 -0700, John Larkin wrote:

When in doubt, use a SEPIC (and maybe an op-amp, but they're little these days):

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Can it cut full PCBs, or only pre-scored ones?

You have to order the boards panelized and scored. Given that, the cut is beautiful.

We figure we'll get a panel of, say, 50 or 100 small boards. Pick+place the bottomside surface mount parts, probably just bypass caps, and solder. Flip and repeat for topside parts. Clean.

Run through our optical inspection machine, then slice up the boards. Hand solder connectors, clean again, and test.

The pick-and-place doesn't like doing single small boards. Fixturing is ugly. The panelized array can have an outer region for the machines to grab.

I like it being borderline impossible. The layout will be fun, and we can hold the line on price.

We're not charging for NRE, so there is no question of ownership.

The CM I use for my prototypes wants even 100x150mm boards panelized two-up. No problem, I put widgets in the kerf so I get freebies, sorta. It's kinda odd having a six-layer board to convert from a .100" center connector to a .050" connector.

Not this one!

It barely fits into a 19" rack.

It would be nice to splatter test circuits in the throwaway area around the small-board array. We don't panalize at Gerber level... we let the board house do it for us. So we can't include extras in the outer region, unless maybe we get the board house to put some extra Gerbers out there. That gets complex.

Every few months, I do a batch of multilayer boards that is just a collection of test circuits that everyone has acumulated.