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rogerdw
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Joined: 22/10/2019
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Posted: 09:52am 21 Nov 2023

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Hi guys, I'm trying to ID a 5V regulator and am not having any success.

It's only 2.1mm x 3.1mm and with 6 pads, no legs.

Thanks for any help

Cheers, Roger

phil99

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Joined: 11/02/2018
Location: Australia
Posts: 2135

Posted: 11:35am 21 Nov 2023

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The codes on small SMD devices aren't always related to the type number. They can be a be anything a large customer wants them to be. The same type may have different codes for each customer.

From your circuit it seems to be an adjustable switch-mode regulator.
The top left pin is the V-feedback pin and from the 18k / 3.3k divider its Vref is about 0.8V.

Do a search for any one with the same pin-out and rated for 15V or more.
Edited 2023-11-21 21:38 by phil99

wiseguy

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Joined: 21/06/2018
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Posts: 1156

Posted: 09:51pm 21 Nov 2023

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Hi Roger maybe some of the following would/could suit ? All ex Digikey

ST1S03
LT3503EDCB#TRMPBF
LT3493EDCB#TRMPBF
TPS40222DRPR
LM2734ZSD/NOPB

If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike

rogerdw
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Posts: 852

Posted: 10:04pm 21 Nov 2023

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Thanks Phil, I was a little surprised that I couldn't find any info, I usually can if I persevere.

I only drew out the full circuit after I'd given up looking through datasheets, so hadn't even considered that it might be a variable regulator. I was assuming it would be a 5V one. The board also has 3.3V one (similar but still a different type and size) which is supplied by the 5V line.

I ended up fitting one off another scrapped board, which fixed the problem, but I'd still like to keep some spares for future potential faults.

I'll check out some more datasheets this morning but this time I won't ignore the variable output ones.

Thanks again.

Cheers, Roger

rogerdw
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Joined: 22/10/2019
Location: Australia
Posts: 852

Posted: 10:09pm 21 Nov 2023

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Thanks for the examples Mike, that may just save me a heap of time.

I've realised I probably caused myself a heap of grief by assuming it was a set output regulator and ignoring the datasheets of all the variable ones. No wonder I couldn't find one with a pinout that looked similar.

Cheers, Roger

phil99

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Posts: 2135

Posted: 10:21pm 21 Nov 2023

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Now you have it working, to be certain you are searching for one with the right Vref measure the feedback pin voltage.
When operating within normal limits it will be the same as Vref.

rogerdw
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Joined: 22/10/2019
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Posts: 852

Posted: 11:57pm 21 Nov 2023

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Well thanks very much again Phil and Mike.

First off, Vref or FB measures .782v

I went through the list you supplied Mike and none showed the layout I thought I had, so I had a closer look and found that while I thought pin 6 was VIN it was actually pin 5 ... and pin 6 (Shutdown) was tied to VIN via a zero ohm resistor because the function is not used.

So it looks like the LT3503 may be suitable as it also says it regulates its feedback pin to 780mV.

I corrected the circuit diagram and added a few details.

This all brings out the fact that even though I enjoy working on my own, having others around to bounce ideas off is probably the single biggest thing that I miss ... but after 35 years and getting close to retirement age ... it's probably not going to change any time soon.

Haha, actually I just hit retirement age today!!!

Cheers, Roger

phil99

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Posted: 12:45am 22 Nov 2023

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One more adjustment to your circuit diagram.
The 18k divider resistor and anode of V109 go to the load side of the output inductor, not the Out pin.

Murphy's friend

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Joined: 04/10/2019
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Posted: 06:54am 22 Nov 2023

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rogerdw said Haha, actually I just hit retirement age today!!!

Does that mean a HAPPY BIRTHDAY wish is in order?

I suppose working for yourself is kind of what I was doing since retiring early (at 60) but just for keeping busy, not working for a living.

rogerdw
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Posted: 01:31pm 22 Nov 2023

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Thanks again Phil, I think I have it worked out now. It's a bit tricky trying to measure everything while still in circuit ... especially when there's a few coils and 0 ohm resistors involved.

Even worse is the rotten conformal coating which is almost impenetrable. I sometimes take to a board with a tiny engraving bit to be able to measure accurately ... and I have an old Polar device which measures very low ohms, but you still have to pay attention.

And yes, thanks Klaus, it is my birthday today.

I just added it up and it is more like 38 years working alone. I've generally enjoyed it and used to be very disciplined but am getting pretty slack in my old age. Winding down I suppose.

Cheers, Roger

Bryan1

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Posted: 07:52am 23 Nov 2023

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Hi Rodger,
Happy Birthday mate

now just remember life does begin at 40 and when one thinks retirement will be easy one will be busier than before.

I'm up at Mt Isa and will be home Sunday night and it will be great to catch up again.

Cheers Bryan

rogerdw
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Joined: 22/10/2019
Location: Australia
Posts: 852

Posted: 09:42am 23 Nov 2023

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Thanks for the birthday wishes Bryan. It crept around fairly quickly and I haven't made any plans yet to quit work. I really need to get some financial advice before I make too many changes.

Sounds like you get around a bit ... Mt Isa ... I assume it's work related.

Yes it would be good to catch up again. Give me a call or a msg whenever you're free and we can organise a get together.

Cheers, Roger

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