Isolators used on STLINK V3 ISOL - Page 1
Forum section: electronics / general

author: smilelolo
author_rank: Newbie
timestamp: June 15, 2022, 05:08:00 am
content: curious on what isolators used on STLINK V3 ISOL.Especially for bidirectional signal like SWDIO some chips for I2C isolations can be used, however, rated generally less than 2Mbps.

author: capt bullshot
author_rank: Super Contributor
timestamp: June 15, 2022, 05:39:08 am
content: I've once seen one opened - but don't have access to it anymore.There's been a bunch of standard isolators, can't remember whether they were optos or the capacitive / inductive coupled type.Anyway and obviously there were far more than required to just isolate the SWD / JTAG lines and no special (like bidirectional or I2C) ones, so I'd guess they've just isolated a large enough number of unidirectional signals and do all the enabling and direction flipping at the isolated side.

author: josip
author_rank: Regular Contributor
timestamp: June 15, 2022, 06:48:16 am
content: BTW, there is TI MSP-ISO for SBW (similar to SWD) with nice documentation. However, it is based on I2C, and limited to 1MHz, so not the one that you are looking for.https://www.ti.com/tool/MSP-ISOhttps://www.ti.com/lit/ug/slau668/slau668.pdf

author: fchk
author_rank: Frequent Contributor
timestamp: June 16, 2022, 11:21:00 am
content: Quote from: smilelolo on June 15, 2022, 05:08:00 amRead the STLINKV3_MODS User Manual:https://www.st.com/resource/en/user_manual/um2502-stlinkv3mods-and-stlinkv3mini-debuggerprogrammer-tiny-probes-for-stm32-microcontrollers-stmicroelectronics.pdfPage 17/18 Section 6.1.2 32-pin edge connector for STLINK-V3MODS (STM32 JTAG/SWD, VCP and bridges)There is an output signal T_SW_DIR on pin 32, which determines the direction on the SWDIO pin. They use this signal to enable/disable unidirectional isolators for this pin.All other pins except for I2C are unidirectional.fchk

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 16, 2022, 04:55:30 pm
content: There are also specialized IC's for USB isolation. You can use these in the intended way by isolating the USB bus, or you may be able to abuse these for some other protocol.

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 16, 2022, 07:13:34 pm
content: Typically, TI and AD have such digital isolators. Very easy to use. No clue what ST have used in the STLINK V3 ISOL, that would require a teardown.But I found this:https://www.st.com/en/development-tools/b-stlink-isol.htmlUnfortunately, I can't see any reference on the picture, but the chips look like wide SOIC which are typical for those digital isolators.Example from AD:https://www.analog.com/en/products/adum2250.html

author: smilelolo
author_rank: Newbie
timestamp: June 16, 2022, 10:38:41 pm
content: Quote from: fchk on June 16, 2022, 11:21:00 amThis is really important information I missed.

author: smilelolo
author_rank: Newbie
timestamp: June 16, 2022, 10:44:33 pm
content: Quote from: josip on June 15, 2022, 06:48:16 amCool, I will get this one (MSP-ISO), which can be used as a general isolator for JTAG, SWD, or SWD+SWO.STLINK V3 ISOL and lots of isolator chips are unfortunately out of stock here in North America.

author: thm_w
author_rank: Super Contributor
timestamp: June 16, 2022, 11:31:12 pm
content: The USB isolator is in stock at TI, but its $50, so a bit more expensive. However, this would be a lot simpler to use, IMO.https://www.ti.com/tool/ISOUSB211DPEVM?login-check=truenico project:https://notabug.org/niconiconi/isousb211

author: gamalot
author_rank: Super Contributor
timestamp: June 17, 2022, 10:04:42 am
content: Identifying these chips is really difficult because high resolution pictures are not available. I believe the part numbers of those isolation chips I gave are correct (except for U34, I can't be sure if it's ISO7761, ISO7762, or ISO7763).There are four chips I can't identify them, my guess is:U19 and U27 are level shifters.U11 is a level shifter or transceiver.U40 should be an op-amp for differential to single-ended conversion.

author: Robotec
author_rank: Contributor
timestamp: June 17, 2022, 11:15:54 am
content: my poor solution is to use a STlink V3 MODS with a Full speed usb chinese isolator and it works just fine.

author: peter-h
author_rank: Super Contributor
timestamp: June 19, 2022, 04:36:00 pm
content: The isolation is not done at the USB interface. Too expensive...It is done at the SWD end. And sure enough the STLINK V3 ISOL does not run anywhere near as fast as the non-ISOL.https://www.eevblog.com/forum/microcontrollers/10-pin-debug-connector-and-stlink-v3-isol-not-reliable/