TIDUF06 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
          4. 2.2.2.2.4 Functional Safety
    3. 2.3 Highlighted Products
      1. 2.3.1 DS90UB953-Q1
      2. 2.3.2 TPS650330-Q1
      3. 2.3.3 IMX623
    4. 2.4 System Design Theory
  8. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Required Hardware
      1. 3.1.1 Hardware Setup
      2. 3.1.2 FPD-Link III I2C Initialization
      3. 3.1.3 IMX623 Initialization
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup
        1. 3.2.1.1 Power Supplies Startup
        2. 3.2.1.2 Power Supply Startup – 1.8 V Rail and Serializer PDB Setup
      2. 3.2.2 Test Results
        1. 3.2.2.1 Power Supplies Start Up
        2. 3.2.2.2 Power Supply Output Voltage Ripple
        3. 3.2.2.3 Power Supply Load Currents
        4. 3.2.2.4 I2C Communications
  9. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 PMIC Layout Recommendations
      2. 4.3.2 PCB Layer Stackup
      3. 4.3.3 Serializer Layout Recommendations
      4. 4.3.4 Imager Layout Recommendations
      5. 4.3.5 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  10. 5Related Documentation
  11. 6Trademarks
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 4.

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 1.2 A, Equation 5 can be used to calculate a minimum saturation current of 1.4 A.

The parameters for the Buck 3 1.1-V rail include:

  • VOUT = 1.1 V
  • VIN(max) = 3.8 V
  • L(min) = 1.0 μH
  • fsw = 2.3 MHz

These parameters yield an inductor ripple current of ΔIL = 340 mA. Assuming a maximum load current of 1.2 A, Equation 5 can be used to calculate a minimum saturation current of 1.4 A.

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.