TIDUBF0 January   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 OX01F10 Imager
      2. 2.3.2 DS90UB933-Q1
      3. 2.3.3 TPS650320-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 OX01F10 Initialization
    2. 3.2 Test Setup
      1. 3.2.1 Power Supplies Start Up
      2. 3.2.2 Setup for Verifying I2C Communications
    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 I2C Communications
  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. 5Tools and Software
  11. 6Documentation Support
  12. 7Support Resources
  13. 8Trademarks
2.2.2.2.3 Choosing the Buck 2 and Buck 3 Inductors

Buck 2 and Buck 3 have a recommended inductor value of 1.0 µH. When selecting a component, it is important to verify the DC resistance and saturation current. The DC resistance of the inductance influences the efficiency of the converter directly – lower DC resistance is directly proportional to efficiency. The saturation requirement of the inductor is determined by combining the steady-state supply current and the inductor ripple current. The current rating needs to be sufficiently high but minimized as much as possible to reduce the physical size of the inductor. Calculate the inductor ripple current using Equation 5.

The parameters for the Buck 2 1.8-V rail include:

  • VOUT = 1.8 V
  • VIN(max) = 3.8 V
  • L(min) = 1.0 μH
  • fsw = 2.3 MHz

These parameters yield an inductor ripple current of ΔIL = 412 mA. Assuming a maximum load current of 600 mA, Equation 6 can be used to calculate a minimum saturation current of 810 mA.

The parameters for the Buck 3 1.2-V rail include:

  • VOUT = 1.2 V
  • VIN(max) = 3.8 V
  • L(min) = 1.0 μH
  • fsw = 2.3 MHz

These parameters yield an inductor ripple current of ΔIL = 357 mA. Assuming a maximum load current of 600 mA, Equation 6 can be used to calculate a minimum saturation current of 780 mA.

Buck 2 and Buck 3 of this design use the TDK® TFM201610ALMA1R0MTAA, which has a current rating of 3.1 A and a DC resistance of 60 mΩ. Additionally, this inductor has an operating temperature of –55°C to 150°C in a very small 2.0-mm × 1.6-mm package.