TIDUF05 August   2022

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 PCB and Form Factor
      2. 2.2.2 Power Supply Design
        1. 2.2.2.1 POC Filter
        2. 2.2.2.2 Power Supply Considerations
          1. 2.2.2.2.1 Choosing External Components
          2. 2.2.2.2.2 Choosing the Buck 1 Inductor
          3. 2.2.2.2.3 Choosing the Buck 2 and Buck 3 Inductors
        3. 2.2.2.3 Functional Safety
    3. 2.3 Highlighted Products
      1. 2.3.1 AR0820 Imager
      2. 2.3.2 DS90UB953-Q1
      3. 2.3.3 TPS650330-Q1
    4. 2.4 System Design Theory
  8. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
      1. 3.1.1 Hardware Setup
      2. 3.1.2 FPD-Link III I2C Initialization
      3. 3.1.3 AR0820 Initialization
    2. 3.2 Test Setup
      1. 3.2.1 Power Supplies Start Up
      2. 3.2.2 Camera Functionality
    3. 3.3 Test Results
      1. 3.3.1 Power Supplies Start-Up
      2. 3.3.2 Power Supply Start-Up—1.8-V Rail and PDB
      3. 3.3.3 Power Supply Voltage Ripple
      4. 3.3.4 Power Supply Load Currents
      5. 3.3.5 Video Output
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 Bill of Materials
      3. 4.1.3 PCB Layout Recommendations
        1. 4.1.3.1 Layout Prints
        2. 4.1.3.2 PMIC Layout Recommendations
        3. 4.1.3.3 Serializer Layout Recommendations
        4. 4.1.3.4 Imager Layout Recommendations
        5. 4.1.3.5 PCB Layer Stackup Recommendations
      4. 4.1.4 Altium Project
      5. 4.1.5 Gerber Files
  10. 5Documentation Support
  11. 6Support Resources
  12. 7Trademarks
2.2.2.2.2 Choosing the Buck 1 Inductor

With an inductance value of 1.5 μH selected, the minimum inductor saturation current must be derived to choose an appropriate inductor for the design. This is the combination of the steady-state supply current as well as the inductor ripple current. To ensure flexibility of the power and serializer base board to higher power image sensors, the inductor is chosen based on each maximum rated output current of the regulator. Equation 3 calculates inductor ripple current:

Equation 3. ΔIL(max)=VOUT×1-VOUTVIN(max)L(min)×fsw

where

  • ΔIL(max) is the maximum peak-to-peak inductor ripple current
  • L(min) is the minimum effective inductor value
  • fsw is the actual PWM switching frequency

The parameters for Buck 1 of this reference design are:

  • VOUT = 3.3 V
  • VIN(max) = 18.3 V
  • L(min) = 1.5 μH
  • fsw = 2.3 MHz

These parameters yield an inductor ripple current of ΔIL = 784 mA. Assuming a maximum load current of 1500 mA, use Equation 4 to calculate a minimum saturation current of 1900 mA.

Equation 4. LSAT≥IOUT,(MAX)+ΔIL(MAX)2

The TPS650330-Q1 device on this design uses a TDK® TFM201610ALMA1R5MTAA, which has a rated current of 2 A and a DC resistance maximum of 152 mΩ. Additionally, this inductor has an operating temperature from –55°C to 150°C in a very small 2.0-mm × 1.6-mm package.