SNVU695A June   2020  – January 2022 LP87702-Q1


  1. 1Introduction
  2. 2xWR Power Supply Requirements
    1. 2.1 Recommended Supply Voltage Requirements
    2. 2.2 Input Supply Current Requirements
    3. 2.3 Input Supply Ripple Requirements
  3. 3Power Solution
    1. 3.1 1.0 V and 1.8 V RF Rail LC Filters
  4. 4Measurements
  5. 5Schematic
  6. 6Bill of Materials
  7. 7Conclusion
  8. 8References
  9. 9Revision History

1.0 V and 1.8 V RF Rail LC Filters

The 1.0 V and 1.8 V regulators are switching at 4 MHz in forced PWM mode and the output is filtered with 470 nH inductor and 2 x 22 µF output capacitors to get good noise performance and stability. Shielded inductor with low DCR is recommended.

For the second stage filter, a 100 nH inductor such as NLCV32T-R10M-EFRD could be used. A ferrite bead could also be used to save cost and space and in this design MPZ2012S101A ferrites are used instead of inductors. The capacitance of the second LC filter includes the decoupling capacitors of the radar supply pins. Additional filter capacitor could help to improve the filtering performance and TI recommends to add a placeholder for at least one additional 22 μF capacitor after the ferrite bead to improve the noise filtering and load transient performance. Based on the performance evaluation on customer boards, if this capacitor is not needed, then it can be removed. The amount of ripple noise and load transient noise that can be tolerated depends on the application and use case. Figure 4-6 shows the ripple performance of LP87702k-Q1 against the AWR ripple specification with MPZ2012S101A ferrite.

Placing the LC filter (ferrite bead and one 22 μF filter capacitor after the ferrite bead) close to the regulator helps to filter the noise close to the source and this could potentially reduce the noise in the area close to the radar device on the PCB. If the LC filter is placed close to radar IC, switching regulator noise is spread in to the PCB and hence has a higher chance of coupling.

On 1.0-V rail, LC filter is split into two paths (RF1_1 and RF1_2) to decouple them from each other for improved noise performance and also reduce IR drop across the second stage inductor.