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FORUM

Energy consumption & setup time CAD SX1261

Semtech Transceivers SX126x family
#1

Hi everyone

We are currently developing an application and want to use the CAD feature to detect LoRa signals. The goal is to stay in a low power mode for a certain time (SX1261 in sleep with data retention), then wake up, perform a CAD and if it detected a signal, go into receive mode and receive the lora frame.

The problem we are currently facing is the long “set up time” before the CAD is actually performed.

–> SX1261 wake up: 570us (instead of 340 as in data sheet)
–> SX1261 set CAD: 5ms (here, only the command SET CAD with specified opcode is sent via SPI and then it waits while the chip is busy which is most of the 5ms.)
–> SX1261 CAD operation ~150us (this time is estimated based on the current consumption measurement and makes sense (2 Symbols SF5, 500kHz = 2x64us = 128us)
–> SX1261 change to sleep: 1ms

Total energy used for this procedure: ~80uJ (which is way more then we anticipated).

CAD_measurement
CAD_measurement2509×1433 481 KB

Does it really take 5ms for the SX1261 before starting the CAD measurement?
Is there a way to minimize this time?

#2

Hi,

How do you measure this wake up time? What are the starting and ending events?

What is the XOSC source in your setup? A TCXO?

#3

Hi,

How do you measure this wake up time? What are the starting and ending events?

Starting event: Wake Up command, Stopping event: When SX1261 is ready (busy flag reset)

What is the XOSC source in your setup? A TCXO?

Yes, a TCXO is used

#4

Hi,

The measurement in the datasheet is done from the NSS rising edge, to avoid any dependency to the SPI implementation.

I suppose then that your TCXO is configured with a 5ms startup time - that would explain the behavior you observe.

#5

Thanks a lot. Yes, the configuration there was 5ms by default.