TIDUDT4A May   2018  – November 2021 AM3351 , AM3352 , AM3354 , AM3356 , AM3357 , AM3358 , AM3358-EP , AM3359


  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 Power Rails Requirements of the System
      2. 2.2.2 Power Sequencing Requirements of the System
      3. 2.2.3 Uncontrolled Power Off
      4. 2.2.4 12-V Input Voltage Rail
    3. 2.3 Highlighted Products
      1. 2.3.1 TLV62568/9
      2. 2.3.2 LM3881
      3. 2.3.3 TLV803
      4. 2.3.4 AM335x
      5. 2.3.5 WL1837MOD
    4. 2.4 System Design Theory
      1. 2.4.1 Power Tree Architecture
      2. 2.4.2 Power Sequencing Solution
        1. Design Steps for DC-DCs
        2. Design Steps for the Sequencer
        3. Design Steps for the Supervisor
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
        1. Connector Configuration of TIDA-01568
        2. Procedure for Board Bring-up and Testing
      2. 3.1.2 Software
        1. Description of Environment Implementation
        2. How to Customize the Processor SDK for This Reference Design
      3. 3.1.3 Software Bring-up Tips
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup
      2. 3.2.2 Test Results
        1. Power-Up and Power-Down Sequence Test
        2. Typical Characteristics of DC-DCs
  9. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 PCB Layout Guidelines
      2. 4.3.2 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  10. 5Software Files
  11. 6Related Documentation
    1. 6.1 Trademarks
  12. 7About the Author
  13. 8Revision History

Design Steps for DC-DCs

Select the circuit topology. The cost, space, and efficiency are key concerns in home appliance design, so select a Buck topology. Use a synchronous converter with integrated FET and high switching frequency to reduce the bill of material cost and size.

Then, select the TLV62568/9. The TLV62568/9 is a high efficiency synchronous converter in a SOT563 package, and typically operates at a 1.5-MHz frequency pulse width modulation (PWM) at moderate to heavy load currents. At light load, the device automatically enters Power Save Mode (PSM) to maintain high efficiency.

Next, set the output voltage, which is adjusted by the resistor divider, as shown in Equation 1. A reference design example is for a 1.8-V power supply, when sizing R4, to achieve low current consumption and acceptable noise sensitivity, to use a maximum of 200 kΩ for R4. Larger currents through R4 improve noise sensitivity and output voltage accuracy, but increase current consumption. In this design, 100 kΩ is selected for R4.

Equation 1. GUID-275B83E9-F291-45DB-8625-A472F3FF0222-low.gif

A feed forward capacitor, C5 of 6.8 pF, is recommended for improving the loop bandwidth to make a fast transient response.

The inductor and output capacitor together provide a low-pass filter. The inductor peak-to-peak ripple current, peak current, and the RMS current are calculated using Equation 2, Equation 3, and Equation 4.

Equation 2. GUID-5B662B60-E551-4880-8522-962D6EDA1568-low.gif
Equation 3. GUID-ABD7C049-5F3B-49C4-AD2A-D2BC8B3B8C05-low.gif
Equation 4. GUID-92C6C16C-56F3-45F2-8C76-BA5DD8B07A98-low.gif

The inductor saturation current rating must be greater than the calculated peak current, and the RMS or heating current rating must be greater than the calculated RMS current. Use 1.5 MHz for fSW. Ensure the chosen inductor is rated for the peak current of Equation 3 and the RMS current of Equation 4.

For this design, the inductor used is the DFE252010F-2R2M=P2 (2.2 µH), with a peak current rating of 3.3 A and RMS current rating of 2.3 A.

The capacitor value and ESR determines the amount of output voltage ripple. The TLV62568 is intended for use with ceramic or other low-ESR capacitors. Use Equation 5 to determine the required RMS current rating for the output capacitor.

Equation 5. GUID-92C6C16C-56F3-45F2-8C76-BA5DD8B07A98-low.gif

For this design, a Murata 10-µF output capacitor is used.