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CC2650 Design Doubts

prasad
Intellectual 500 points
Other Parts Discussed in Thread: CC2650

Hi Everyone!!!

I am developing a custom board based on CC2650. I am referring to the designs given by TI:

A) SensorTag(document: tidu862)

B)CC2650 Development Kit

Following are my doubts:

1) In tidu862, pins 1(RF_P) & 2(RF_N) are connected to antenna circuit via 15pF caps & there is no cap connected to inductor L2 whereas in CC2650EM-7ID schematic (available on ti's site), those pins are connected directly to antenna circuit & L11 inductor is connected in series to a capacitor C31 of value 6.8pF.

(a) Which to follow?

(b) What are the advantages/disadvantages in either?

2) It is mentioned in Technical Ref. Manual(TRM) of  CC2650(document: swcu117f) on pg 26 & 413 that to have lowest power, connect VDDR to internal DC-DC, which is pin DCDC_SW. In this case:

(a) VDDS_DCDC should be connected to VDDS?

(b) VDDR & VDDR_RF should be shorted?

(c) VDDR/VDDR_RF should be connected directly to DCDC_SW?

(c) The decoupling capacitor(s) connected to VDDR & VDDR_RF shown in either of the above mentioned documents should be still connected?

3) Also, it is mentioned in TRM that if Global_LDO is used to supply to VDDR, VDDR & VVDR_RF should be shorted & DCDC_SW should be left floating. Then:

(a) Why in reference designs, DCDC_SW is connected to VDDR, VDDR_RF through an inductor of 10uH?

(b) What exact differences(pin connections) are there in either mode: Internal DCDC & Global LDO ?

Please Help Me!

- Prasad.

  • 0
    TI__Guru** 106705 points
    Hi Prasad,

    1) These are DC-blocking capacitors, and as you point out they are placed differently in the SensorTag than in our other reference designs. There are no differences in terms of performance between these two options, BUT, the SensorTag approach will not work with external biasing.

    2) Connecting VDDR to the internal DCDC is not the same as connecting it to the DCDC-SW pin. The internal DCDC requires an external 10 uH inductor and a 10 uF capacitor to operate properly, this is clearly stated multiple places in the documentation. The output of the DCDC is on the inductor/capacitor node. The correct connections and required components are shown in the reference designs.

    3) The only difference between DCDC and LDO mode is that you can remove the 10 uH inductor in the latter case.

    Cheers,
    Fredrik