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
2.2.2.2.1 Choosing External Components

For simplicity, the efficiency of the buck regulators is assumed to be 85% for these operating conditions, and the efficiency of the LDO is given by Equation 5.

Equation 2. ηLDO=VOUTVIN
System and Buck 1 currents calculated assuming 85% switching regulator efficiency are given in Equation 5.

Table 2-2 shows the load capability of each regulator compared to the requirements of the camera module. The TPS650320-Q1 device is capable of supplying the system power with plenty of margin to account for variations between typical and maximum current variation.

Table 2-2 Regulator Load Capability
REGULATOROUTPUT VOLTAGE (V)MAX CURRENT (mA)REQUIRED CURRENT (mA)
Buck 13.8800160
Buck 21.8600122
Buck 31.1600170
LDO3.330033

After determining that the TPS650320-Q1 device is suitable based on the power requirements, the external components can be chosen quickly based on the data sheet recommendations, simplifying the design process. These recommendations are shown in Figure 2-5 and Equation 5.

GUID-1172DD63-52B2-401B-BE6A-AB5B8E99BC81-low.gifFigure 2-5 TPS650320-Q1 Typical Application Circuit
Table 2-3 TPS650330-Q1 Recommended Components
COMPONENTDESCRIPTIONVALUEUNIT
CVSYS,VSYS_SVSYS and VSYS_S decoupling10µF
CPVIN_B1Buck 1 input capacitor10µF
LSW_B1Buck 1 inductor

2.2

µH
COUT_B1Buck 1 output capacitor10µF
CPVIN_B2Buck 2 input capacitor10µF
LSW_B2Buck 2 inductor1.0µH
COUT_B2Buck 2 output capacitor10µF
CPVIN_B3Buck 3 input capacitor10µF
LSW_B3Buck 3 inductor1.0µH
COUT_B3Buck 3 output capacitor10µF
CPVIN_LDOLDO input capacitor1.0µF
COUT_LDOLDO output capacitor2.2µF

The high, fixed PWM 2.3-MHz switching frequency enables the use of small inductors with a fast transient response. A value of 2.2 µH is typically recommended for the BUCK1 channel output. This value helps to minimize the inductor ripple current.

With the inductance value chosen, the design now needs an inductor with a proper saturation current. This is the combination of the steady-state supply current as well as 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 inductor ripple with Equation 3:

Equation 3. GUID-E90486CD-8F03-47AB-B8A1-2A7229ABA7CA-low.gif

where:

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

The parameters for this reference design using the TPS650330-Q1 are:

  • VOUT = 3.3 V
  • VIN(max) = 18.3 V
  • L(min) = 2.2 µH
  • fSW = 2.3 MHz

These parameters yield an inductor current of ∆IL = 535 mA. The maximum current draw of the system through this regulator is 327 mA. The minimum saturation current is calculated as:

Equation 4. GUID-82D9BCB1-CD66-4116-ABA0-99DF84FAEA12-low.gif

The TPS650330-Q1 device on this design uses a Murata® LQM2MPN2R2NG0, which has a rated current of 1.2 A and a DC resistance maximum of 138 mΩ. Additionally, this device has an operating temperature from –55°C to 125°C and comes in a very small 2-mm × 1.6-mm package.