Help identify part : "W4A3" SOT23-5 adjustable switching DC step down regulator - Page 1
Forum section: electronics / repair

author: flaco
author_rank: Newbie
timestamp: November 25, 2021, 08:49:37 pm
content: Dear eevblog forum membersI 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 EnablePin 2 is GNDPin 3 is connected to the inductor wich has a E markingpin 4 is connected to the 5V input rail.Pin 5 is feedbackThey 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 FLASHAll 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=4A few of them do not have marking information though:SP6669https://eu.mouser.com/datasheet/2/146/SP6669-1888959.pdffound an older datasheet with the exar brand, marking is QBWWRP504Nhttps://eu.mouser.com/datasheet/2/792/rp504-ea-1770399.pdfAN6008https://static.ananavitek.com/uploads/2019/07/AN6008.pdfalso found ST1S12XXhttps://eu.mouser.com/datasheet/2/389/cd00181873-1796762.pdfwith no marking indication

author: fzabkar
author_rank: Super Contributor
timestamp: November 25, 2021, 09:30:08 pm
content: Can you determine the feedback voltage by measuring the two feedback resistors?What are the date codes on the other ICs?

author: flaco
author_rank: Newbie
timestamp: November 26, 2021, 08:37:14 pm
content: Thank you fzabkar,Quote from: fzabkar on November 25, 2021, 09:30:08 pmGood idea. The feedback voltage is 0.6vI 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 workingAnd I measured the feedback voltages in circuit since I left the resistors.Quote from: fzabkar on November 25, 2021, 09:30:08 pmIl will say 2016 on the VL811 and on a flash, and 2017 on the "DisplayLink" DL-3900-N

author: fzabkar
author_rank: Super Contributor
timestamp: November 26, 2021, 09:18:27 pm
content: 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.

author: flaco
author_rank: Newbie
timestamp: November 27, 2021, 06:19:35 pm
content: Quote from: fzabkar on November 26, 2021, 09:18:27 pmI also searched for just W4. Found a few "SMD code books" but nothing related to a regulatorQuote from: fzabkar on November 26, 2021, 09:18:27 pmI 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 !

author: fzabkar
author_rank: Super Contributor
timestamp: November 27, 2021, 07:59:41 pm
content: 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.

author: flaco
author_rank: Newbie
timestamp: December 07, 2021, 08:54:06 pm
content: 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.htmlThe 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.