LM2743 Reference Design - Synchronous Buck Converter, for Point Of Load Applications: 3.3V Input, 1V @ 2.5A Output

  Design Specifications

Inputs Outputs #1
VinMin=3.3 Vout1=1
VinMax=3.3 Iout1=2.5
   Design Resources

LM2743 Reference Design

  Additional Resources


LM2743 Product Folder
LM2743-19AEVAL Evaluation Board
LM2743EVAL Evaluation Board
   Bill Of Materials

Part Manufacturer Part# Attributes
C10 Vitramon VJ0805Y104KXXAT 0.1u F
C13 RUBYCON 6.3ZAV470 470u F
C14 TDK C2012X5R0J106M 10u F
C20 RUBYCON 6.3ZAV470 470u F
C21 TDK C2012X5R0J106M 10u F
C4 Vitramon VJ0805Y103KXXAT 10n F
C5 Vitramon VJ0805A101KXXAT 100p F
C6 Vitramon VJ0805Y222KXXAT 2.2n F
C8 TDK C3216X7R1E225K 2.2u F
D2 ONSEMI BAT54 0.32 V
L2 Coilcraft DO1813P-332 HC 3.3u H, 0.04 Ohms
M1 Siliconix SI3460DV
M2 Siliconix SI3460DV
R1 Dale CRCW080510R0FRT6 10 Ohms
R11 Dale CRCW08051003FRT6 100k Ohms
R14 Dale CRCW08052742FRT6 27.4k Ohms
R15 Dale CRCW08051502FRT6 15k Ohms
R16 Dale CRCW08051002FRT6 10k Ohms
R7 Dale CRCW08053161FRT6 3.16k Ohms
R8 Dale CRCW08054992FRT6 49.9k Ohms
U1 National Semiconductor LM2743

  Design Description

The design uses a LM2743 synchronous controller utilizing external high side and low side N-channel MOSFETs operating at 600kHz nominal based upon the frequency set resistor value (R8). Careful PC board layout is critical to achieve low switching losses and clean, stable operation. The switching power stage requires particular attention. Few points to note for this design are:

1) Decoupling capacitors are close to IC pins as possible. Keep separate power ground plane.

2) Input and output capacitors are connected to the power ground plane; all other capacitors are connected to the signal ground plane.

3) High current paths are very short.

4) Multiple MOSFETs have been used to reduce the conduction and switching losses

5) Feedback connections are short and direct and routed away from any noisy traces (i.e. switch node).

6) High-side MOSFETs are as close as possible to the controller



  Schematic

Example Schematic Showing Connection for all Components.


  Waveforms


NSC0303-Output Voltage Ripple

NSC0303-Switch Node

NSC0303-Transient Response

NSC0303-voltages at start up