TF360 Power Supply Discussion

News & updates for the upcoming 68060 accelerator

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terriblefire
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TF360 Power Supply Discussion

Post by terriblefire »

So as many of you may be aware up to now i've used linear regulators on my TF boards. They've worked fine because the CPUs have been at 5V and the regulators really only existed to drive the CPLDs and in some cases SDRAM.

Unfortunately the TF360 is not so straightforward. Yes I managed to get it to work with a big phat linear regulator but there are two problems. First is that it will not work in this form with a stock CD32 PSU. Second is that a linear regulator gets hotter than holy hell (thats what has the heatsink on it).

So I have decided that its time to go switched mode on the TF360. I have built these badgers before but I wanted to have a bit of a discussion about the best options out there. I want a really efficient 5V to 3.3v design that can be done with relatively low profile components. The constraints of the CD32 being what they are.

This is the only way i can see the TF360 will be viable in a stock CD32 without a new PSU.
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Re: TF360 Power Supply Discussion

Post by exxos »

Guess it depends on how many amps you need. There is a lot of intergrated chips but they tend to have poor internal MOSFETs for the switching. So once you get around the 1amp mark your mostly getting stuck with more complicated things.

I use a integrated chip for my PSUs. Probably the most efficient and runs the 5v rail, but needs a inductor and diode. The inductor is a issue as pissy small ones will get red hot so you don't end up better off.

I think the 060 needs around 7 amps on the 3.3v rail. So it will be tricky to get a small footprint with high power output. You could copy my 5v design and use a smaller inductor, which will run hotter. But the chip stays cool.

There may be better 3.3v solutions but the ones I went for were more adjustable then fixed voltages. Probably look at Texas intergrated chips and see what's there first. But you need the rdson like 20mR or lower else it will cook when pushing a few amps.

Its a bit of a minefield unfortunaly , and regulation is also a factor as I found, some chips really suck.
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Re: TF360 Power Supply Discussion

Post by terriblefire »

Yeah all my previous SMPSU setups had hot inductors. the alternative is to go for the biggest linear reg i can find.... arent there off the shelf 10A SMPSU designs?
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Re: TF360 Power Supply Discussion

Post by exxos »

I've not checked for 10amp ones.. But while there maybe ICS to do it, your gonna be stuck with a large inductor like i use. That's a lot of space but runs stone cold.

While the ic i use is efficient , pushing 5 amps constant will heat up a whole gnd plane.. I'm not at home right now to check what numbers I used. But there's a lot of info in this thread ...
https://www.exxosforum.co.uk/forum/viewt ... ?f=9&t=255
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Re: TF360 Power Supply Discussion

Post by 8 Bit Dreams »

You, guys, must be living into 20th century :lol: :lol: :lol:
there are A LOT of modern power regulators nowadays ;)
What about this one from muRata:
https://power.murata.com/pub/data/power ... 2a_a00.pdf
2Amps, and NO HEAT at all...
using these in my 128K Toast Rack Speccy with a buttload of expansions plugged in - works excellent :P

and this is just one example, there are tons of other stuff.. Even D-Pack's can provide 2A without any heatsink.. :idea:
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Re: TF360 Power Supply Discussion

Post by terriblefire »

Its about 5A short of what we need though.
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Re: TF360 Power Supply Discussion

Post by exxos »

Those are low power stuff , try looking at 10amp stuff.
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Re: TF360 Power Supply Discussion

Post by 8 Bit Dreams »

Oh!
since Steve used LM78xx i was sure 2A is enough, will check for beefed one and come back soon :geek:

Have built a custom power supply for my Sinclair QL a while ago, and used DC-DC step-down converter like this:
https://www.ebay.de/itm/DC-DC-10A-Step- ... 3759663515
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Re: TF360 Power Supply Discussion

Post by terriblefire »

exxos wrote: Sun Apr 21, 2019 5:16 pm Those are low power stuff , try looking at 10amp stuff.
I just checked the 68060 datasheet. It recommends 2A @ 3.3v... :/
11.2.1.1.1 Linear Voltage Regulator Solution. This solution uses a linear voltage regulator to supply 2 A at 3.3 V. This solution is inexpensive; however, conversion efficiency of only
up to 65% can be achieved. Figure 11-1 shows a solution using power BJTs. This solution
would be used primarily for applications that are cost sensitive, but not power sensitive. The
suggested linear solution meets the 3.3 V± 5% MC68060 specifications.
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Re: TF360 Power Supply Discussion

Post by exxos »

The guy who did the Atari 060 was recommending 7 amps. Might be just easier to measure the current on the thing... But then double it for over clocking and headroom.
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