CC2652P: Does it back off from 20dB to 14dB sometimes?

Hi Raphael,

Thank you for reaching out! I will look into this asap, in the meantime can you share the SDK version you are seeing this behavior in? As a quick test, can you try transmitting coded packets at 20dbm in SmartRF Studio 7 to see if you see similar power there?

Best Regards,

Jan

Hi Jan,

The SDK version is 8.31.00.11.

While we haven't measured the power consumption when operated from the SmartRF Studio 7, we have already done several tests where we measured the effective TX output power in SmartRF Studio operation and also in the host-test-app. Across the band, the values have been 2-4dB lower than expected (but not lower than that), but I think this is more due to our non-ideal impedance matching / balun circuit on the PCB.

We will measure the power consumption in those modes in the coming days.

Best regards,
Raphael

HI Raphael,

Understood. Please let me know the results of the power measurements to confirm, but based on your observations it seems the drop-off is not happening on SmartRF.

Best Regards,

Jan

Hi Jan!

Here are the measurements with the Smart RF studio: On the left, you see the configuration, on the right the measurement. I measured the three BLE advertising channels 37, 38 and 39:

Thank you for your help!

Best,
Raphael


PS: Sorry, for some reason it doesn't want me to upload the picture with channel 39. The average current there is 90.89mA

Hi Jan!

Do you have any update? That is a very important topic to us.

Best regards,

Raphael

Hi Raphael,

I apologize for the delay as Jan is currently on vacation and will be returning 7/13.  He had mentioned raising this behavior to the attention of BLE R&D but I'm not sure of any updates on this front.  We will try to provide you with an update as soon as possible.

Regards,
Ryan

Dear Ryan and Jan,

What is the status of this topic? Do you have an update? Thank you very much for your help!

Best,

Raphael

Hi Raphael,

Apologies for the delay let me follow up with our R&D experts on this to confirm.

Best Regards,

Jan

Hi Raphael,

Got a response back and this seems to be expected. We have a backoff table for the CC13X2P device which should also apply CC2652P. You may find it below:

https://dev.ti.com/tirex/content/simplelink_cc13xx_cc26xx_sdk_8_33_00_16/docs/ble5stack/ble_user_guide/html/ble-stack-common/link-layer-cc13xx_cc26xx.html#tx-power-backoff-table-for-cc13x2p-devices

As you can see on 1M PHY it maxes out at 14dBm in channel 39.

Best Regards,

Jan

Dear Jan,

Thank you very much for that answer! It explains why on the 1M advertisements, it has reduced TX power in the last packet (marked red in the picture below).

But the TxPowerBackoffTable is at 20dBm for coded-phy for all channels. So I don't see how it explains the reduced power consumption in the coded-phy-advertisement set in the four peaks after the red marking.

Can you please ask the Engineering team about that?

Thank you and best regards,

Raphael

Hi Raphael,

Apologies for the delay again. Looking into this with the HW team, I believe this is done to meet FCC requirements regarding PSD. I believe we need to update our documentation as that table does not mention this.

Best Regards,

Jan

Hi Jan,

Do you have some more precise updates here? Is there a way to disable this if we don't target FCC certification?

Hi,

Apologies for the delay. I don't believe there is a way to disable this in the SDK at this time.

Best Regards,

Jan

Alright... But can you at least tell me if there is any compliance reason for this behavior of the BLE Stack in the EU? At least according to my understanding of EN 300 328, there shouldn't be.
And the same question for FCC regulations: Is this the reason for this BLE stack behavior?