TIDUEJ8C January   2019  – May 2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 MSPM0G1506
      2. 2.3.2 LMG2100R044
      3. 2.3.3 INA241
      4. 2.3.4 TPSM365
      5. 2.3.5 TMP303
    4. 2.4 System Design Theory
      1. 2.4.1 MPPT Operation
      2. 2.4.2 Buck Converter
        1. 2.4.2.1 Output Inductance
        2. 2.4.2.2 Input Capacitance
      3. 2.4.3 Current Sense Amplifier
        1. 2.4.3.1 Shunt Resistor Selection
        2. 2.4.3.2 Current Measurement Resolution
        3. 2.4.3.3 Shunt Resistor Power Dissipation
      4. 2.4.4 Switching Regulator
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
        1. 3.1.1.1 TIDA-010042
        2. 3.1.1.2 ITECH-IT6724H
        3. 3.1.1.3 Chroma, 63107A
      2. 3.1.2 Software Flow
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup
      2. 3.2.2 Test Results
  10. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 Loop Inductances
      2. 4.3.2 Current Sense Amplifiers
      3. 4.3.3 Trace Widths
      4. 4.3.4 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
    7. 4.7 Software Files
  11. 5Related Documentation
    1. 5.1 Trademarks
    2. 5.2 Support Resources
  12. 6About the Author
  13. 7Revision History

2.4.2.1 Output Inductance

Continuous conduction mode (CCM) is desired to maintain a high efficiency while delivering the constant current required for battery charging. When the input voltage range, output voltage and load current are defined, it leaves the inductor value as the design parameter to maintain CCM.

Therefore, the desired ripple current is defined. A typical value is 0.2 to 0.4 times the output current. Firstly, the loop speed in PV system is not that fast, so the value of inductance can be higher. Secondly, it is important to reduce the ripple voltage of the output capacitor. Finally, the size of inductor should not be too big to save space. So, 0.3 is selected as the coefficient of ripple current.

Considering 16A maximum output current, and ignoring the voltage drop on the FETs and resistance of the inductor, giving:

Equation 1. L×∆ITOFF=VO

The worst case of CCM for a fixed output voltage converter is when Toff is maximum, also, the bigger the value of inductor is, the easier the converter stays in CCM, then the equation above can be transformed into:

Equation 2. L≥VO×(1-VOVin_max)∆I×fsw

In this application, Vin_max is 60V, fsw is the switching frequency 250kHz. When the output voltage is 24V, the inductance needs to be higher than 12μH. When the output voltage is 12V, the inductance needs to be higher than 8μH. In the case of the same size, an inductor with a smaller inductance can have a larger saturation current. Finally, 10μH is chosen as the value of the inductance.

TIDA-010042 Power Stage SchematicFigure 2-11 Power Stage Schematic