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

2 xWR Power Supply Requirements

The power supply design challenges for TI radar processors are described below, and the TI radar processors are addressed in this design.

  1. 1.0 V/1.3 V RF and 1.8 V RF rails have very tight ripple specifications in (μV range) and it is very challenging to meet such a low ripple specifications for switching regulators.
  2. Traditionally, LDO’s are used on RF rails, but LDO solution suffers from poor thermal performance and it increases cost.
  3. A low cost LC filter is used between switching regulators and AWR supply rails to filter the ripple. An LC filter should be carefully selected as a large inductance will cause load transient settling or ringing issues and also an increased voltage drop across them. A smaller inductance won’t provide enough filtering performance.
  4. All the power rails should be within ±5 % (except 1.2 V with -5% and +10% requirement) of nominal voltage level and increased ringing will result in violation of specification.
  5. All the ringing should ideally settle very quickly (before ADC start-time) to avoid spurs related to power supply settling noise.
  6. Higher regulator switching frequency helps to reduce the LC filter size and also increases regulator bandwidth to minimize the undershoot or overshoot during the load transient. All TI radar PMICs supplying the RF rails use 4 MHz or higher switching frequency.
  7. LC filter is placed outside the switching regulator regulation loop. L (ferrite bead) is placed close to the regulator output and C of this LC filter includes the decoupling capacitors of the AWR supply pins.
  8. The PCB size is very limited and hence it is necessary to have a very small power management solution size in case of USRR, SRR, and some MRR applications.
  9. Increased board temperature will affect the AWR RF performance and hence it is necessary to reduce the effect of the board temperature rise due to the PMIC and regulators heating. Also some of the radar applications have plastic housing and thermal management becomes very critical.
  10. System level safety requirements for radar sensors are increasing and hence it is necessary to have PMICs which meet system level safety goals (ASIL-B or ASIL-C at PMIC level).