Re: Si5351 current consumption #chat

Shirley Dulcey KE1L

Since the code is open source, you can easily determine the frequencies that the programs are using. Add Serial.print() statements in the appropriate places and look at the results on the serial monitor on your computer. For the version with the Etherkit library you'll have to add them to the library code rather than to your own sketch, but that also comes with source. You'll want to remove those when you put the system in use because they will slow down frequency changes.

On Sat, Mar 14, 2020 at 10:03 AM Shirley Dulcey KE1L via Groups.Io <> wrote:
Power consumption of CMOS logic depends on operating frequency; the higher the frequency, the more power that is used. CMOS gates use almost no power in either saturated state (on or off), but consume more during transition between the states. Gates cannot switch in zero time; increased frequency means that a larger percentage of time is spent in the non-saturated state, therefore more power.

The two libraries are probably choosing different combinations of PLL and divider settings, with Etherkit going for a higher PLL frequency. That would account for the difference in power consumption that you are seeing, as it would lead to higher power consumption in both the PLL and the dividers.

On Sat, Mar 14, 2020 at 9:48 AM Eduard Voiculescu <yo9ict@...> wrote:

A new chat has been created:

Hi guys,

I am comparing the current consumption of the Si5351 under the same conditions (same VCC, same 68 ohm load resistor, full power, unused outputs turned off, steady carrier within the 20m band, same frequency) in two software cases:
1. , which looks just about right in terms of power draw to what the U3S is having (~33mA)
2. Within the Etherkit 5351 library (, which you may be also aware of. The instructions are as follows:
  si5351.init(SI5351_CRYSTAL_LOAD_0PF, 27000000, 0); - external TCXO
  si5351.drive_strength(SI5351_CLK0, SI5351_DRIVE_8MA); - set max drive for output 0
  si5351.set_freq(1409717000ULL, SI5351_CLK0); - set frequency to 20m;PLL settings are calculated by the library
  si5351.output_enable(SI5351_CLK0, 1); - enable output 0;other are by default turned off
This yields about 43mA current draw by the Si5351 (10mA more than U3S/OE1CGS sketch).
Adding a couple of instructions to turn off the unused outputs clocks:
results in a lower current, ~ 39mA, but still about 6mA higher than U3S/OE1CGS sketch.
I suspect there is a catch, like finding the exact PLL specifications or turning off the unused PLL or anything like this, but I cannot figure it out. I'm just hoping anyone has any ideas.
Thank you,
Eduard YO3ICT

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