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CC1200: Questions on RESET_N pin of CC1200

Yuanchen Zhu
Intellectual 340 points
Part Number: CC1200

Dear TI Friend,

Question1 :

  We happened to find Tx spurious emission from CC1200 (have solved it). During the debugging, we attempted to use an external supply to ensure no unwanted signal coupled in supply.

However, we do find one thing: Even we disconnected the series component, i.e. power supply for CC1200 is cut off, still there is near 3.3V power on the rail. Using evaluation board, we find IT IS the RESET_N pin seems to supply the power to the chip. Wonder if that's what it is supposed to be doing. Anyone can share some thoughts on this?

Question2:

 We understand it is better off and safer to use a pull-up resistor to deal with reset pin.  Right now in our development procedure, our board does not have a pull-up resistor for reset_n pin. We find when power off and on again, there is something wrong, and it is required to dowload program again to do the job. Same code working with demo board CC1200(demo board has a pull-up) seems to have no problem. Thus, we are corncerned about RESET pin. Anyone has some thoughts on this? Or how can we avoid this by software for time of being?

If I am not clear on the description, please point out.

Yuanchen Zhu

  • 0
    TI__Genius 11810 points

    Hi, 

    Can you provide a drawing for question 1 to show which traces you have cut. 

    A pull-up resistor in combination with a capacitor is needed to get a proper reset of the chip. 

    -Simon 

  • 0 in reply to Simon J
    Intellectual 340 points

    Hello Simon

    As in https://www.ti.com/lit/pdf/tidr233 for evaluation board , we simply disconnected the jumper wire of "VDD_REG" (plus we did not connect NET "3V3A" either) from the interface of CONN_8(P4), checking with disconnecting jumper wire one by one, we are pretty sure it is the RESET_N pin still supplied the power. Just curious about the intention of this. 

    Bty, for Q2, found out it was actually MCU side pin conflict problem. And now just wonder what value of the resistor and cap would you recommend or the methdology to ensure that we choose the appropiate value?

    Yuanchen

  • +1 in reply to Yuanchen Zhu
    TI__Genius 11810 points

    Hi Yuanchen,

    Ok, that is most likely some remaining charge on all of the decoupling capacitors on VDD_REG. 

    Since you are controlling the reset signal from a MCU, no resistor or capacitor is required. 

    -Simon 

  • 0 in reply to Simon J
    Intellectual 340 points

    Fine. But really, was trying to see Tx output when VDD_REG is disconnected from start, and still can see stable output Tx waveform, plus still have time to confirm the voltage with DVM. Thanks, anyway.

    Yuanchen