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
2.2.2.2.2 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 4 calculates inductor ripple current.

Equation 4. 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 = 3.8 V
  • VIN(max) = 18.3 V
  • L(min) = 1.5 μH
  • fsw = 2.3 MHz

These parameters yield an inductor ripple current of ΔIL = 873 mA. Assuming a maximum load current of 1.5 A, use Equation 5 to calculate a minimum saturation current of 1.9 A.

Equation 5. LSAT≥IOUT,(MAX)+ΔIL(MAX)2

The TPS650330-Q1 device on this design uses a TDK® TFM201610ALMA1R5MTAA, which has a rated current of 3.1 A and a DC resistance maximum of 110 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.