Electronics > Projects, Designs, and Technical Stuff

Cheap, ultra low power RTC to periodically wake microcontroller from power-down?

(1/8) > >>

I wanted a rude username:
Some microcontrollers have excellent power-down current consumption, but this gets orders of magnitude worse when they are running, even at low frequencies. E.g. at 3.3 V the Padauk PMS134 draws 100 nA in power-down but 40 µA on its internal low-speed oscillator. This would completely drain a CR2032 in less than a year.

There are excellent RTCs like the Micro Crystal RV-8803-C7 which can be used to periodically wake the microcontroller from power-down via an interrupt, avoiding this waste of power. The RV-8803-C7 draws roughly 250 nA, and is even temperature compensated. However, at $1.60 per unit in volume it nukes all the cost saving of the 10¢ Padauk.

Is there a budget RTC for this purpose, in the < 1 µA range, which isn't in a big (SOP) package? Temperature compensation is a nice-to-have but definitely not required. Internal crystal preferred but also not required.

krish2487:
Is the RTC a necessity or will periodically waking up the micro sufficient?

Is something like this
https://www.digikey.com/product-detail/en/texas-instruments/TPL5110DDCT/296-38830-2-ND/5130143
a viable solution for what you are wanting to do??
:-)

Yansi:
Why do it complicated?

Use an MCU with a low power timer (or even the RTC) suited for periodic wakeup in the first place.

For example STM32L011, if you want something small with low consumption.

Howardlong:

--- Quote from: krish2487 on December 03, 2019, 12:37:31 pm ---Is the RTC a necessity or will periodically waking up the micro sufficient?

Is something like this
https://www.digikey.com/product-detail/en/texas-instruments/TPL5110DDCT/296-38830-2-ND/5130143
a viable solution for what you are wanting to do??
:-)

--- End quote ---

Nice device, I wasn't aware of those, thanks for the info.

To the OP: I was discussing these super cheap MCUs the other day with some colleagues, and the end result of the conversation was that in many cases, the family feature sets are limited compared to more mature and industry standard product lines. If you need to spend $0.50 to add the right functionality to a $0.10 MCU, it quickly negates the cost benefit.

Furthermore, there are plenty of mainstream options that can provide <1uA 32kHz crystal clock on chip and if you don't mind doing your RTCC in software they're cheap. You can use low power watchdogs if it's not time critical.

jhpadjustable:

--- Quote from: I wanted a rude username on December 03, 2019, 12:17:18 pm ---Is there a budget RTC for this purpose, in the < 1 µA range, which isn't in a big (SOP) package? Temperature compensation is a nice-to-have but definitely not required. Internal crystal preferred but also not required.

--- End quote ---
How about the PCF85063? Run current 0.22µA (typical) 0.6µA (max), available in a variety of small packages from SO-8 down, 80¢/1 or $54/100 at Digi-Key. The bad news is you have to bring your own tuning fork crystal.

Maybe the Padauk route isn't the best route. If I understand correctly, you don't really need the core to be running, just the RTC and its oscillator. The tinyAVR 0-series seems worth a look. Typical power consumption at 3.3V in standby mode, with just the RTC and external (EDIT: no, internal) low-speed oscillator running and most other interrupt sources available, appears to be less than 2µA under 85°C. The actual retail price from Digi-Key is 40¢/1.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod