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How do I measure MCU power dissipation on Synergy kits and correlate to data sheet values?

Latest Updated:10/13/2016

Question:

What is the best method for measuring MCU power dissipation on my Synergy kit? How can I duplicate the metrics from the data sheet?

Answer:

There are several elements that need to be considered when initializing a Synergy MCU for taking meaningful power measurements. Some of the most important ones are listed below. By following these guidelines you should be able to duplicate the metrics fund in the appropriate device data sheet.   

1) Determine which clock setting you want to use and set them. For example, do you want to use the LOCO or MOCO? What frequency do you want them to run at? Synergy Data sheets report MCU operating and standby current for a variety of modes (like High-Speed mode, and Medium-Speed mode), operating mode (Normal or Sleep), and with various clocks and peripherals operating or disabled.

2) Determine and set the code you want to execute during you power measurement cycle. Because the Synergy MCUs use advanced caching to improve performance you need to construct you testing code precisely. For example, if you use a single operation While Loop, like while(1), the cache will be refreshed and accessed very often. This increases power dissipation. If you se a series of NOOP instructions in your While Loop instead, you will find power dissipation metrics correlate with the data sheet values. Without this approach the values will be higher. For example, on the S3A7 the data sheet 5.1mA number for High-Speed mode, Normal operation, at 16 MHz can be as much as 7.3 mA (also depending on the settings for MOCO and LOCO).

3) Disable and other clocks such as MOCO and LOCO if you don't want them included in the power measurement.

4) Use the supplied test points on your Synergy Kits (for example, on the DK-S3A7 kit you would measure the current drop across the precision 50-mOhm resistors R1 and R42 using connector J22 for MCU current and J24 for analog current).

Follow the above guidlines and you should be able to measure and correlate your readings with those in the appropriate Synergy device data sheet.