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CC2592 compare to CC2591

speedo38
Intellectual 310 points
Other Parts Discussed in Thread: CC2591, CC2500, CC2592, CC2511, CC2538

hello,

we are using the CC2591 with the CC2511 and we won't to do a new product but with a CC2500. I think the best is to plug the CC2500 with a CC2592 . But I've got some questions.

1) With the CC2591 we need to be paid attention to the power supply line, for the CC2592 it seem less constraint , I'm right ?

2) I'v got the impedance of the output and input of the CC2592, but I couldn't find for the CC2500 and the CC2592 on the datasheet.


3) On the CC2592 schematics the Pin ANT is link to VDD by a self. Why it is different to the CC2591 ?

Thank you for your help

David

  • 0
    TI__Guru 56590 points

    Hello,

    1)

    Correct, the CC2592 is more stable. Although we still recommend you to use filtering to achieve a stable supply.

    2)

    For the CC2500 it is given in the data sheet as 80 + j74. This is the load seen from the RF_P and RF_N pins towards the antenna. But when you put it together with the CC2592 you should not consider this as the output impedance for the CC2592 is more crucial. The CC2592 does not match well to any impedance but it will accept a quite wide range. Think of it as an area in the smith chart with acceptable impedances. Start by looking at the the CC2538-CC2592EM design. There can be placed a shunt component in between the CC2500 and the CC2592. This can be used if some tuning is necessary.

    3)

    It is just a design choice i guess. The external inductor connected to VDD is used to set an external bias for the LNA.

  • 0 in reply to Eirik V
    Intellectual 445 points

    Just to add a little bit to Eirik's reply:

    1) The CC2591 required inductors (or T-lines) on the VDD supply pins. These have been integrated on CC2592, so only good decoupling (capacitance) is needed.

    2) The disadvantage of stating an impedance is that customers then often try to match the impedance instead of copying our reference design. This can cause problems, since it's not just the impedance at the carrier frequency that's important, but also the impedances at all the harmonic frequencies, especially the first 5. Please follow Erik's suggestion, and look at how the matching has been implemented on the CC2538-CC2592EM - both sides of CC2592. The shunt component between the transceiver and CC2592 is not used, but we found that if you place CC2592 closer to CC2538 than we do in the current reference design, a shunt inductor was needed to compensate some of the inductance lost in the traces.

    3) The Antenna pin has a DC feed, and it's important that you copy this part accurately. This is a slight re-architecture of the PA/LNA to improve stability and performance.

    Best  regards,

    EWI

  • 0 in reply to Espen Wium
    TI__Guru 56590 points

    Thanks EWI :)

  • 0 in reply to Espen Wium
    Prodigy 10 points

    I need to bring the CC2592 closer to the CC2538 due to real estate reasons.  How is the inductor across the differential RF out chosen?  Also, the chain of passive leading to the antenna would have insertion loss instead of tuning with the PIFA itself.  if I follow the layout of the reference design fully up to the output of the CC2592, can you share your load pull plot or where it was measured; then I can design my PIFA to match without any passive?

    Thanks!

    SD

  • 0 in reply to Steven Downs
    Intellectual 445 points

    Hello Steven,

    The inductor value must be chosen through experimentation. Start with a high value (e.g. 12nH multilayer) and work your way down until you obtain the best sensitivity (you can optimize for TX parameters like Pout and harmonics too, if you want)

    The passives on the antenna pin aren't just for RF matching, they provide DC to the PA too. You'll need at least a decoupling cap, a DC feed inductor, and a DC block if you want to connect it to a PIFA.

    Best regards,

    EWI