SLAAEP3 December   2025 ULC1001

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Acronyms
  5. 2 Introduction
  6. 3 Impedance Response
    1. 3.1 Piezo Only
    2. 3.2 Lens Cover
    3. 3.3 Lens Cover System (LCS)
  7. 4 Equivalent Circuit Model of LCS
  8. 5 LC Filter for LCS
  9. 6 Water Cleaning
  10. 7 Power Consumption
  11. 8 Reliability
  12. 9 Other Tests
    1. 9.1 De-ice
    2. 9.2 Mud Cleaning
    3. 9.3 Optical Interference
    4. 9.4 Waterproof Capability
  13. 10Resources

5 LC Filter for LCS

The LCS-FL-RNG15 requires a voltage as high as 140Vpp to expel water efficiently. However, the maximum voltage output for DRV2911 is limited to 35V, necessitating a voltage gain of 4x to meet the voltage requirement. To achieve this goal, a simple LC filter has been designed and implemented. A passive LC filter can exhibit voltage gain near the resonant frequency, allowing the voltage across the inductor or capacitor to exceed the initial input voltage. This phenomenon is due to the energy stored in the inductor and capacitor oscillates back and forth, causing the voltage across the components to become much larger than the input voltage. Note that, despite this increase in voltage, a power gain cannot be achieved.

The amount of voltage gain at the resonant peak is primarily determined by the quality factor (Q) of the circuit. A higher Q results in a sharper peak and a greater voltage gain. Remember the power output is still limited by the power input. An increase in voltage is accompanied by a decrease in current.

The gain is maximized at the resonant frequency of the LC circuit, which is calculated using the formula:

Equation 1. f0 =12πLC

For a series RLC circuit,

Equation 2. Q = 12πf0CR

Theoretically, the quality factor can be infinitely high. In reality, parasitic resistances and capacitances limit the maximum achievable Q and thus the maximum voltage gain. To reduce the gain, the resonant frequency of the LC filter can be a certain distance from the resonant frequency of the load. The further of the two resonances, the smaller of voltage gain is applied to the load.

The Default LC Filter for LCS-FL-RNG15 in ULC1001-DRV2911EVMFigure 5-1 The Default LC Filter for LCS-FL-RNG15 in ULC1001-DRV2911EVM

In ULC1001-DRV2911EVM, the LC is set at L= 22uH, and C = 47nF, yielding a calculated cut off resonant frequency of 110 kHz. The resonant frequency of the LCS-FL-RNG15 is 66 kHz. The frequency distance yields a gain of 4.

Figure 5-2 shows the measured impedance response of the LCS with the default LC filter. The measured resonant frequency of the LC filter is 112.7kHz with a low resistance of 0.94Ω. The impedances of the two modes at 30kHz and 66kHz are also significantly lowered when measuring the impedance the LCS and the LC filter as a whole.

Impedance Response of LCS with an LC FilterFigure 5-2 Impedance Response of LCS with an LC Filter