nRF24l01+ 2450BM14A0002 + RFX2401C + 2450BP14D0100. Using VDD_PA pin for controlling PA/LNA.

[Fadi Bunni]

Hello Community,

So I am building a RF system from scratch based on the nRF24l01P transceiver with a PA/LNA, using a balun for impedance matching and a band filter for filtering unwanted frequencies.

 

As stated in the data sheet the PA/LNA RFX2401C on page 5, can be set in 3 different modes: Shutdown(0,0), RX Active(0,1) and TX active (1,x). I know that I don't care about the shutdown mode, since I only need the RX and TX active modes. As seen on the schematics, the RXEN is always pulled up to high, this means that I can control the TX active, RX active, modes by changing the TXEN from 0 to 1. For this I want to use the VDD_PA pin to control the TXEN, such that when I am transmitting from the transceiver the VDD_PA will be set to high which in turn will set the TXEN to high, meaning the PA/LNA will be set to TX active mode (as in power amplification mode) and if I set the transceiver in receiving mode the VDD_PA will be set to low, which in turn will set the TXEN to low, meaning the PA/LNA will be set to RX active mode (as in LNA mode). Now my question is, will this above described method work? or do I need to use a external GPIO from a MCU to control the TXEN pin? The datasheet on nRF24l01P does not explain when and if the VDD_PA goes high or low?

Furthermore, what do you think about the schematics, anything that pops out and needs to be changed or added?

Thank you for your time.

Regards
Fadi Bunni

[HenryTR]

Hello,

I see a potential concern, regarding the 0.3pF capactior between the RFX2401C ANT pin and the 24508P1400100 IN pin.  I think this should be tied to GND according to the RFX2401C datasheet page 7.  It is my understanding that this cap is thesame as the C3 cap in Figure 3.

Is this schematic up to date with the design that you built and tested?

I am curious since I am currently designing a PCB for a remote control car.

-Henry

[Fadi Bunni]

Here is the newest schematics, tested and it works :)

[HenryTR]

Thanks!  I had a question regarding how the RFX2401C module switches between TX and RX.  It looks to me like since RX is logic high, it will be in receive mode; unless TX is also logic high.  So NRF24L01 only raises VCC_PA high when it is transmitting.

Is my understanding correct?

[Fadi Bunni]

Yes