nRF5340 +3 dBm TX Power with ESB – VREQCTRL has no effect?

[H. Dekker]

We are trying to increase the TX output power on the nRF5340 when using Enhanced ShockBurst (ESB). According to the product specification, the nRF5340 supports +3 dBm TX power, but the documentation also states that a higher RADIO regulator voltage must be enabled using VREQCTRL for this to work.

I found a related topic here: nRF5340 Radio TX Power – Nordic Q&A

We added the following function to our project to enable high-voltage operation for the RADIO regulator:

void radio_power_enhance(void)
{
#if defined(NRF_VREQCTRL)
	LOG_INF("\nIncrease Radio TX Power: Enabling VREGRADIO High Voltage Mode\n");
	NRF_VREQCTRL->VREGRADIO.VREQH = 1;
	while(!NRF_VREQCTRL->VREGRADIO.VREQHREADY);	
	LOG_INF("VREQHREADY: %s\n\n", NRF_VREQCTRL->VREGRADIO.VREQHREADY ? "true" : "false");
	LOG_INF("RADIO regulator is now operating at high voltage (1.9V).\n");
#else
	LOG_INF("High voltage radio mode not supported on this device.\n");
#endif
}

We call this function at the start of main() before initializing ESB:

// Increase Radio TX Power for nRF5340
#if defined(NRF_VREQCTRL)
	radio_power_enhance();
#endif

We then call:

esb_set_tx_power(ESB_TX_POWER_0DBM);

Based on the documentation, this should now output +3 dBm due to the increased voltage regulator level.

We are testing on a nRF5340-DK, using nRF Connect SDK v3.0.1. However, when measuring RSSI at the receiver side (also ESB), there is no measurable difference in signal strength, whether we enable radio_power_enhance() or not — even at greater distances.

Question:

Does the VREQH method (VREQCTRL.VREGRADIO.VREQH = 1) correctly enable +3 dBm TX power when using ESB on the nRF5340?
Or is there something else we need to configure in order for the higher TX output to actually take effect?

Any insights would be appreciated!

[Kenneth]

Hi,

Just call esb_set_tx_power(ESB_TX_POWER_3DBM); The ESB library will ensure that the neccessary registers are set, for implementation check out update_radio_tx_power() in esb.c.

Kenneth

[H. Dekker]

Hi Kenneth,

Sorry for my late reply, I was abroad for a while.

I tested the above, but ESB_TX_POWER_3DBM is not a valid value. I only have the options ESB_TX_POWER_0DBM or negative dBm values.

Herke

[Kenneth]

Hi,

Sorry, you can call esb_set_tx_power(3).

Kenneth

[H. Dekker]

Hi Kenneth,

I understand that I can use esb_set_tx_power(3);. I can also use esb_set_tx_power(10) or even esb_set_tx_power(50);. But these values are ignored if they’re not supported, so in all cases the output power stays at 0 dBm.

I did test everything properly using Nordic SDK 3.0.2 and the ESB examples from the same SDK folder. I also added the RSSI function for testing. However, my RSSI values don’t change — the signal strength doesn’t improve.

[Kenneth]

Hi,

If you measure using RSSI radiated, it will likely not be able to distinguish 3dB difference, due to the other factors influence so much. Can you please try to measure conducted, and also connect a spectrum analyzer? If you have a PPK II you can even measure the current consumption, I expect you will see current increase for the transmission.

Kenneth