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CC1200: CC1200RHBT

ibrahim
Prodigy 10 points
Part Number: CC1200

Tool/software:

Hello,

I have some questions regarding the CC1200 at 868MHz:

  1. In the CC1200 datasheet, Table 4.1 shows that the maximum voltage on the analog pin is 2V. However, when we supply 3.3V as per application note (SWRR121), the DC voltage at Pin 17 (PA) is 2.7V because of the R171 (10 ohms) (basic voltage divider rule). Is that correct? 
  2. The above calculate is under the assumption that Pin 17 internal load impedance is 50 ohms, is this assumption correct?

  3. Can I use different supply voltages, for example, 3.3V for all analog pins (i.e., Pin 17) and 3V for all digital pins (i.e., Pins 12, 5,1,13,15, etc.)?

  4. In the CC1200 datasheet, Table 4.14 shows the load capacitance for the crystal oscillator as 10pF. However, in application note (SWRR121), it is 15pF. Which of them is the correct value?

  • 0
    Mastermind 6060 points

    1: Yes. R171 is in place to reduce the DC some on this pin. 

    2: No. Refer to table 4.10.1 in the CC1200 datasheet.

    3: No, see table 4.1

    4: Note that load capacitance is the two load caps in parallel + the parasitics. Meaning that if the ref design uses 15 pF it contributes with 7.5 pF to the total load.  

  • 0 in reply to TheGhostOf
    Prodigy 10 points

    Hello, 

    Thank you that was very helpful,

    Follow-up regarding the second question:

    5. I believe the data in table 4.10.1 refer to the RF optimal load impedance connected to Pin 17 (i.e., antenna), right?

    6. In the case that we feed DC to Pin 17 and assume the load impedance of the Pin 17 is:

    Case 1: 30+j30, you will 2.82 V fed to Pin 17, how is this applicable considering the Table in 4.1? (i.e., Max Voltage on analog pins=2 V),

    Case 2: 50 ohms, 2.75 V fed to Pin 17, how is this applicable considering the Table in 4.1? (i.e., Max Voltage on analog pins=2 V),

    Follow-up regarding the third question:

    The table in 4.1 suggest voltages at digital pin can be from -0.3 to VDD+0.3V range. 

    and for supply voltage (VDD, AVDD_X) can be from -0.3 to 3.9V range. therefore, Can I use different 3.3V supply voltages for (VDD, AVDD_X) and 3V voltage for digital pin?

    Thank you. 

  • 0 in reply to ibrahim
    Mastermind 6060 points

    5: Correct. But that means that the internal impedance is not 50 ohm. 

    6: For this, the PA is not regarded as a analog pin, using the ref design is safe. 

    The chip is designed to use the same supply on all pins. 3.0 V and 3.3 V could work but you will have leakage between the different power segments through the ESD diodes.