LowPowerLab Forum

Hardware support => Low Power Techniques => Topic started by: phibes4000 on May 28, 2017, 06:58:59 AM

Title: Human Solderable Low Power RTC
Post by: phibes4000 on May 28, 2017, 06:58:59 AM

Hi,

Any recommendations for a low-power RTC that can run at <=3.3V and is in a human-solderable package?  I can do SMD with hot air, but draw the line at 'no lead' options like QFN - no reflow just yet.  I really like the features of the Abracon and Ambiq RTCs but they are QFN.

I'm more concerned with low power consumption than accuracy - a drift of 1-5s/day is OK, and would be compensated for with an hourly radio-based sync (poor-man's NTP - a long way from PTP).

Being able to handle interrupts and have the 328P MCU effectively slaved to RTC (as the AB1805 can do) is a nice to have to minimise power use.

Thanks,

Lee

Title: Re: Human Solderable Low Power RTC
Post by: TomWS on May 28, 2017, 07:20:24 AM

Dallas Semiconductor had some SOIC/TSSOP RTCs that are accurate and 'solderable'.  The AM18x5 is tough to beat from a quiescent current perspective, but tricky to solder. 

If your budget is in the single to low double digit uA domain, the DS chips will probably work for you.

Tom

Title: Re: Human Solderable Low Power RTC
Post by: captcha on May 28, 2017, 07:21:31 AM

I've been using the MCP79410-I/SN with great success to revive my Mega328 from sleep. Comes in SOIC package (biggest size under DIP, very much hand solderable).

Product page here:
http://www.microchip.com/wwwproducts/en/MCP79410 (http://www.microchip.com/wwwproducts/en/MCP79410)

Pricing as per RS is around AU$1.45
http://au.rs-online.com/web/p/real-time-clocks/7263949/ (http://au.rs-online.com/web/p/real-time-clocks/7263949/)

power consumption about 1.2uA @ 3.3V

Title: Re: Human Solderable Low Power RTC
Post by: phibes4000 on May 28, 2017, 08:09:17 AM

Thanks. That MCP chip looks pretty good. If it had support for an external interrupt it would be ideal.

Title: Re: Human Solderable Low Power RTC
Post by: TomWS on May 28, 2017, 09:13:44 AM

Actually, I forgot about a chip I used a few years ago, PCF2129A, from NXP.  0.65uA, +/-3PPM with INTERNAL TXCO, 20pin SOIC, either SPI or I2C interface and lots of interrupt choices.

I forgot because its too big for most of my applications now, but it is a very nice chip...  Did I mention +/-3PPM with INTERNAL oscillator - no xtal needed.

Tom

Title: Re: Human Solderable Low Power RTC
Post by: phibes4000 on May 28, 2017, 09:39:15 AM

Quote from: TomWS on May 28, 2017, 09:13:44 AM

Actually, I forgot about a chip I used a few years ago, PCF2129A, from NXP.  0.65uA, +/-3PPM with INTERNAL TXCO, 20pin SOIC, either SPI or I2C interface and lots of interrupt choices.

I forgot because its too big for most of my applications now, but it is a very nice chip...  Did I mention +/-3PPM with INTERNAL oscillator - no xtal needed.

Tom

It won't handle a pulse interrupt (can do simple interrupt on pin change vs ground), but otherwise looks very nice.  Includes a temperature sensor!