SX1280 TCXO/ Crystal versus Power Mode

Thread Starter

joseph20480

Joined Nov 15, 2023
5
Dear community,

I have developed a board with SX1280 and i meet some difficult.
In fact, the clock signal on crystal (52Mhz) make "pause" often ( maybe each transmit).
My configuration :
1. internal DC-DC power instead of Internal LDO
2. Crystal Osc 52Mhz instead of TCXO (52Mhz).

Capture d'écran 2024-02-27 162945.pngI try to debug my board with help of SX1280 evaluation board( no problem with the eval board).The only difference :
>> TCXO instead of Crystal . (power mode is the same).

My question, do you have already use the SX1280 on crystal AND with DC-DC power mode ??
There is no information in datasheet... i'm lost.
 

jrb_sland

Joined Dec 24, 2021
24
Dear community,

I have developed a board with SX1280 and i meet some difficult.
In fact, the clock signal on crystal (52Mhz) make "pause" often ( maybe each transmit).
My configuration :
1. internal DC-DC power instead of Internal LDO
2. Crystal Osc 52Mhz instead of TCXO (52Mhz).

View attachment 316421I try to debug my board with help of SX1280 evaluation board( no problem with the eval board).The only difference :
>> TCXO instead of Crystal . (power mode is the same).

My question, do you have already use the SX1280 on crystal AND with DC-DC power mode ??
There is no information in datasheet... i'm lost.
All the TCXOs I have ever used have at least three active pins, i.e. VDD, GND, and OUT [or Fo = signal out]. Your schematic doesn't show a Vdd connection [often a separately regulated precision 3.00 volts] for your part labelled "XTAL4" .
Page 17 of the Semtech data sheet*** for the SX1280 labels pin 4 as either XTA [of the XTA/XTB simple crystal connection that I see in your schematic] or as the input from a TCXO, with no connection to pin 6 [XTB]. See the suggested schematic in Figure 15.3 on page 147 of the data sheet showing decoupling ferrite beads & a 100 nF bypass capacitor on the Vdd input & the 1 nF output coupling capacitor. Does the SX1280 require setting up [programming] an internal control register to distinguish between crystal & TCXO operation, or does it auto-detect the crystal?
The DC/DC power mode should not be related at all to the crystal/TCXO operation, but I've not studied the SX1280 data sheet in depth in its entirety. That is your job. Hope this helps!
*** https://media.digikey.com/pdf/Data Sheets/Semtech PDFs/SX1280-81_Rev3.2_Mar2020.pdf
 

Thread Starter

joseph20480

Joined Nov 15, 2023
5
All the TCXOs I have ever used have at least three active pins, i.e. VDD, GND, and OUT [or Fo = signal out]. Your schematic doesn't show a Vdd connection [often a separately regulated precision 3.00 volts] for your part labelled "XTAL4" .
Page 17 of the Semtech data sheet*** for the SX1280 labels pin 4 as either XTA [of the XTA/XTB simple crystal connection that I see in your schematic] or as the input from a TCXO, with no connection to pin 6 [XTB]. See the suggested schematic in Figure 15.3 on page 147 of the data sheet showing decoupling ferrite beads & a 100 nF bypass capacitor on the Vdd input & the 1 nF output coupling capacitor. Does the SX1280 require setting up [programming] an internal control register to distinguish between crystal & TCXO operation, or does it auto-detect the crystal?
The DC/DC power mode should not be related at all to the crystal/TCXO operation, but I've not studied the SX1280 data sheet in depth in its entirety. That is your job. Hope this helps!
*** https://media.digikey.com/pdf/Data Sheets/Semtech PDFs/SX1280-81_Rev3.2_Mar2020.pdf
thanks for your reply.
1. "The DC/DC power mode should not be related at all to the crystal/TCXO operation "
You have right, i haven't read information about this... but..

2. TCXO need power supply, crystal not. My orginal schematics works with simple crystal. I have to try with a TCXO (and little modification on my prototype).
 
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