Abracon AB1805 hardware alternative due to supply issues?

I’ve been using the AB1805 watchdog per an application note AN023 Watchdog Timers | Datasheets | Particle


I’ve been very happy with the approach and haven’t had a Boron in the field go offline since.
However, as I order my next batch of boards, it seems this component has extended lead times due to the Silicon supply chain shortages. Does anyone know a suitable replacement with minimal firmware/hardware changes? Right now trying to decide between… delaying the PCBA order until the parts are in stock or continuing with the order but without the Watchdog functionality. Normally, I’d just proceed with the order and then hand solder on the parts when they come in but in this case, it’s tiny 16-VFQFN that I wouldn’t know how to solder myself once the parts are available again.

Since I’m not the only one using this design, I figured I’d ask the community of any known alternatives or workarounds. I’d rather not deploy devices in the field without this functionality but not sure on what options I have.

Any suggestions or guidance is appreciated!

@jgskarda ,

Oh man, I am getting tired of this on-going chip shortage. I do not have a good answer other than to go back to the separate clock and TPL5010.

I hope Particle has a better answer as, like you, I appreciated being able to follow an Application Note for this part of my design.



So looking at other parts in the same family from Abracon here are the possible alternatives that I’ll be looking at further and scrutinizing.

  • AB1815-T3 - Same functionality but with SPI instead of I2C. Requires PCB rework and Firmware library rework. Requires an additional GPIO pin.
  • AB0805-T3 - Does not provide RESET pin for watchdog. Still functional Deep Reset. Unsure if changes can be made to accomplish Watchdog like functionality via RST.
  • AB0815-T3 - SPI version of the AB0805 (wouldn’t make sense as I’d use AB0805-T3 (I2C) before this)

Here are the two diagrams for each:


I’ll need to study this in more detail, but on the surface, it seems the AB0805-T3 could possible be a replacement. However, it likely would not provide the “reset” functionality as part of the watchdog in the same way the application note defines it. I currently do not use the interrupt to wake from hibernate. I only use Watchdog/reset and then the deep power down 30 second reset.


If anyone else has insights or guidance I’d sure appreciate it. On the surface, I’ll keep investigating if I can use FOUT/nIRQ currently used for RTC wake-up from Hibernate via interrupt pin as the Reset for the watchdog as I currently do not require an interrupt for waking from hibernate.

@rickkas7 - I believe you were key contributor to the Application note using AB1805. On the surface, do you think the AB0805 could suffice as a replacement while maintaining the deep power down reset (30 second power down) and hardware watchdog reset? Any recommendations?


hey, I feel your pain. What I wanted to say is a big Thank you for making your analysis public here, since others (like me) can learn.

So, thank you!


Thanks @gusgonnet - I’ll be studying this in much more detail in the coming days. Just found out this morning about the availability issue. Here is what seems to be the earliest available from various suppliers:

Newark: More stock available to supplier lead times which is approximately 12/13/21
Online Components: 9,770 can ship 1/17/22
Mouser: On Order: 11,997 (does not provide expected delivery date) - Quote requested.

If these dates hold… I might be OK given my product ship dates but would sure be nice to have an alternative plan.

Maybe with enough collaboration from the community we can have a Application Note V2 to either use the SPI version instead of the I2C version (AB1815) or a variation using AB0815. What was great about the Application note is it just worked and implementing this was vastly simplified using a library.

I’ll keep posting here as I learn more.

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I wrote the application note, the library, designed the PCB, and reflowed it myself! It should be pretty straightforward to switch to SPI. I have several other libraries that support switching between I2C and SPI and it’s usually pretty easy.

And the pins are pretty flexible and we don’t use all of the INT pins, so it’s probably possible to switch to using a different set of outputs but I’d have to actually research it to be sure.

I’ll see about ordering the parts and spinning a SPI breakout for when I have time to work on it again.


That would be fantastic @Rickas7. Just to be clear… your initial opinion is best to migrate to AB1815 (SPI version)? If so, what’s the best way for me to help? I might be able to sketch something up in Eagle given your open source files within the Application Note and start with the similar feather wing equivalent but for SPI instead of I2C. I’d be happy to order the board and ship several to you as well. Happy to do whatever I am I capable of to help move this along. I’m thinking many others in the Particle Community could benefit in having an alternative as well.

The AB1815 (SPI equivalent) has significant availability (14K+ available via DigiKey). Here was the stock of AB1815:

I also reached out to Abracon directly to understand possible lead times this was their response (which is not encouraging :frowning: ):
“We already sell AB1815, AB1805, AB0815, AB0805 series RTC through distribution….but you might not find stock as inventories have been depleted and production facing extended lead time. This part is currently allocated and no lead time known at this time. We recommend planning your production a year in advance .”

Let me know the best way to help. In the meantime, I may start looking at updating your FeatherWing board to be SPI.

In general I2C is easier since it saves a GPIO and is a much easier redesign if it’s just switching outputs, but I’m not 100% sure that’s possible.

To cover both bases, SPI should be a pretty simple software change, so I might as well prepare for both. For anyone designing a new board it just provides another option.

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@rickkas7 - Good stuff… is the Ambiq AM1805 a direct 1:1 replacement for the Abracon AB1805? Zero firmware/zero hardware change? I just looked closer at the application note documentation, your GitHub repo as well as other repos/libraries/google searches and several places reference it being a clone/direct replacement including several of your links:

  • The Abracon AB1805 (and its identical relative, the Ambiq Micro AM1805), is an I2C-connected watchdog and real-time clock chip. AN023-watchdog-timers

  • Class for using the AB1805/AM1805 RTC/watchdog chip. AB1805_RK documentation

*Looks like the AM1805 is what is used on the [TrackerOne RTC] I suspect the library is based off of that/also used for tracker one? (Tracker SoM datasheet | Datasheets | Particle)

If so, there might be a few sources of the AM1805AQ in stock (although not what I’d consider normal channels such as DigiKey/Mouser/Etc.). Could you confirm?

***UPDATE: Per this news article… I’m guessing the parts are identical and Abracon basically bought the licensing and/or design for the RTC from Ambiq. If so, that would be simply fantastic and I spent a lot of energy scrambling to find an alternative for no reason. Abracon Corporation Announces Strategic Channel Partnership With Ambiq Micro for New ULP Real Time Clock Product Family | Benzinga

I didn’t do a comparison of every page of their spec sheets, but the “features” page is nearly a 1:1 match in the words used except a find/replace on the company name and part number. It also includes this nice little sub note/disclaimer:

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Can anyone with 100% certainty confirm AM1805AQ from Ambiq is a 1:1 direct replacement for the AB1805-T3? If so, I ordered the necessary quantity of AM1805AQ directly from Ambiq and received a tracking number. However, I currently have 100+ PCBAs on order and would supply AM1805AQ to the PCBA assembly house to use instead of the AB1805-T3. I would sure hate to find out after full PCBA assembly of all 100+ units that it’s not a 1:1 direct replacement.

I’m going to do my best to try and hand solder via hot air re-work station on some earlier PCBs I have but I’ve never attempted reworking a component that small before.

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SOLUTION: The lot of AM1805AQ from Ambiq arrived today and as I hoped… it is confirmed to be a 1:1 direct replacement/identical part. For anyone else searching for availability of AB1805-T3 you can order AM1805AQ directly from Ambiq Here. I ordered the supply I needed 4-5 days ago and they arrived today in the US from the the Netherlands. I was able to de-solder an AB1805-T3 from a prior board, clean up the PCB and solder on a new AM1805AQ. Everything checks out and works properly. So my immediate need is met. Posting here in case anyone else is in the same scenario.

That sure was a fun challenge to solder that tiny thing by hand. Maybe some of you seasoned electronics Guru’s are used to it but certainly was the smallest components I ever dealt with. Some solder paste, a hot air re-work station, isopropyl alcohol, flux and some solder wick were all required in this delicate process. Took me 3 tries but eventually soldered it correctly.


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