SLVAF76 August   2021 TPS62901 , TPS62902 , TPS62902-Q1 , TPS62903 , TPS62903-Q1

 

  1.   Trademarks
  2. 1Applications With Limited Area
    1. 1.1 Best TPS62903 Configuration to Reduce Size
    2. 1.2 Design Example
  3. 2Applications With High Efficiency and Thermal Requirement
    1. 2.1 Conduction Losses in the MOSFET
    2. 2.2 Conduction Losses in the Inductor
    3. 2.3 Switching Losses in the MOSFET
    4. 2.4 Losses in the Input and Output Capacitors
    5. 2.5 Analysis and Recommendations
  4. 3Conclusion

1.2 Design Example

This section describes how to best design a buck converter to support 6 V input supply, and step it down to 1.2 V output and support up to 3 A. The same steps can be taken to design it for other design requirements.

Selection of components:

  • Inductor: The 6 VIN to 1.2 V output voltage allows the use of 0.68 µH inductor with reasonable inductor current ripple if 2.5 MHz is chosen. A small size 2.0 mm × 1.6 mm 0.68 µH inductor can be used for this such as the “DFE201612E-R68M#” from Murata.
  • Input capacitor: Input voltage requirement for this design is only 6 V. Therefore, 10 µF with only 10 V rating can be used.
  • Output capacitor: The recommended output capacitor in the data sheet is 22 µF. In this example, the output is set to 1.2 V, therefore only 6 V voltage rating can be used.
  • Feedback: 1.2 V VOUT is one of the 16 options VSET can support, to save area and achieve better accuracy, the internal voltage divider can be used in this example. Internal feedback should give a total system accuracy of ±1.25% versus 1.9% if external feedback is used.
  • Mode and Smart Configuration: A low VOUT can tolerate low switching frequency with good inductor current ripple. Both 1 MHz or 2.5 MHz can be chosen. However, the goal is to have the smallest solution size possible, and 2.5 MHz allows the use of a 0.68 µH inductor with acceptable ripple. Power save mode is preferred to provide high efficiency at light loads. Thus, 26.1 kΩ is connected on the Mode/S-CONF pin to GND.
  • EN, Soft start, and PG: If there is no need for soft start capacitor and Power Good features, these pins can be left floating. The EN pin can be connected directly to VIN. These add some additional BOM savings.

Here is a suggested schematic for this example:



Figure 1-1 Design Example Schematic
Table 1-1 Components PCB Area
Component Size and Rating Area
CIN 10 µF, 10 V, 0805, X7R 2.5 mm2
COUT 22 µF, 6 V, 0805, X7R 2.5 mm2
Inductor 0.68 µH, 2.0 mm × 1.6 mm × 1.2 mm, 33 mΩ 3.2 mm2
Mode/S-CONF resistor 26.1 kΩ, ±1%, 0402 0.5 mm2
TPS62903 Buck Converter, 1.5 mm × 2.0 mm 3.0 mm2
Routing Estimated Routing Area 13.3 mm2
Total Area Routing plus components 25 mm2

Figure 1-2 provides a layout example. CIN, COUT, and the inductor L are placed as close as possible to the pin of the device. The SW node trace is kept small for better noise performance. Vias are added on GND, VIN, and VOUT traces to help improve thermal dissipation of the board.



Figure 1-2 Layout Example