Help identify part : "W4A3" SOT23-5 adjustable switching DC step down regulator

[flaco]

Dear eevblog forum members

I am trying to identify a broken SOT 23-5 adjustable switching DC step down regulator marked "W4A3".

I found alternatives, however it seems each of them need different feedback resistors and inductor so I'd rather replace it with the original parts. I would appreciate if anyone could point out what they are.

At least thanks for reading anyway.

Their pinout is identical to other parts such as LM3674, AN6008 or SY8009AAAC :
Pin 1 is Enable
Pin 2 is GND
Pin 3 is connected to the inductor wich has a E marking
pin 4 is connected to the 5V input rail.
Pin 5 is feedback

They are in a Kensington SD3600 USB docking station that has been powered with a wrong supply.
There are 7 of these on the board, each powering a rail:
- 3.3v and 1.2v, always on and powering the USB3 VL811 and USB2 FE1.1s hubs
- 1.2v and two other unknown voltages, for the "Displaylink" DL-3900-N chip (haven't found a datasheet) and its ram
- 1.05v and I believe 3.3v for the RTL8211E network and its FLASH

All their output inductors are the same and marked with the letter "E". (haven't found if it indicates their value)

4 of them have burn marks so I believe they are all dead. The RTL8211 network chip is also dead since its 3.3v and 1.05v rails are shorted. Maybe everything else is also dead, but it's worth trying.


I opened all the 180 datasheets from mouser with no luck.
https://eu.mouser.com/c/semiconductors/power-management-ics/voltage-regulators-voltage-controllers/switching-voltage-regulators/?package%20%2F%20case=SOT-23-5&topology=Buck&pg=4

A few of them do not have marking information though:
SP6669 https://eu.mouser.com/datasheet/2/146/SP6669-1888959.pdf found an older datasheet with the exar brand, marking is QBWW
RP504N https://eu.mouser.com/datasheet/2/792/rp504-ea-1770399.pdf
AN6008 https://static.ananavitek.com/uploads/2019/07/AN6008.pdf
also found ST1S12XX https://eu.mouser.com/datasheet/2/389/cd00181873-1796762.pdf with no marking indication

[fzabkar]

Can you determine the feedback voltage by measuring the two feedback resistors?

What are the date codes on the other ICs?

[flaco]

Thank you fzabkar,

Can you determine the feedback voltage by measuring the two feedback resistors?

Good idea. The feedback voltage is 0.6v

I didn't remove the resistors but removed all the broken regulators, the RTL8211E, and placed flying LDOs to feed the 3.3v and 1.2v rails.
This way I could test that the USB3 main chip and the USB2 hub are working 
And I measured the feedback voltages in circuit since I left the resistors.

What are the date codes on the other ICs?

Il will say 2016 on the VL811 and on a flash, and 2017 on the "DisplayLink" DL-3900-N

[fzabkar]

I was thinking that "A3" might be some kind of date code, but I can't see how it relates to 2016 or 2017. :-?

I guess you could search for PDFs using advanced parameters:

https://ipv4.google.com/search?q=filetype%3Adoc+OR+filetype%3Apdf+"absolute+maximum"+converter+OR+regulator+"0.6V"+"sot23-5"+stepdown+OR+"step+down"

Personally I would just use a device with the same pinout and feedback voltage.

[flaco]

I was thinking that "A3" might be some kind of date code, but I can't see how it relates to 2016 or 2017. :-?

I also searched for just W4. Found a few "SMD code books" but nothing related to a regulator

Personally I would just use a device with the same pinout and feedback voltage.

I was concerned by the inductor and switching frequency. Too bad I don't have a LCR meter or function gen to get its value.
If I don't find the original reference, this is what I will do.

Thank you fzabkar !

[fzabkar]

I found some photos of the SD4000 model, but none were detailed enough to see the part markings. I was hoping it would provide some clues.

[flaco]

Hi,
Small update since I now have another SD3600 which suffered the same overvoltage.
This second one is more recent since the chips are dated from 2020. 4 rails are shorted to ground after removing the regulators so I believe it is not suitable for repairs.

The regulators in this one have a "LDCPK" marking, and it seems that these could be SILERGY SY8088AAC according to this datasheet (from the collection I made during my previous search) :
https://pdf1.alldatasheet.com/datasheet-pdf/view/1132524/SILERGY/SY8088AAC.html
The only thing that could be wrong is that the date code is a number on some photos I found and here it is the letter C, however it could be that they started using letters when they reached 2020.

I believe I will go for this one.
It is interesting to note that it is rated for 1A when most of the other regulators in the same package I found earlier on mouser are 600mA or less.