LM2727 Reference Design - Synchronous Buck Controller, High Efficiency Output: 10-13.2V Input; 2.5V @ 5A Output

  Design Specifications

Inputs Outputs #1
VinMin=4.5 Vout1=2.5
VinMax=5.5 Iout1=3
   Design Resources

LM2727 Reference Design

  Additional Resources


LM2727 Product Folder
LM2727EVAL Evaluation Board
   Bill Of Materials

Part Manufacturer Part# Attributes
Cboot Vishay VJ1206Y104KXXAT 0.1u F
Cc1 Vishay VJ1206A100KXXAT 10p F
Cc2 Vishay VJ1206A391KXXAT 390p F
Cc3 Vishay VJ1206Y122KXXAT 1.2n F
Cin TDK C3216X5R1A106K NumCaps=1, 10u F
Cin1 Sanyo 16MV470WG 470u F, 0.036 Ohms
Cinx TDK C3216X5R0J225M 2.2u F
Co1 Sanyo 16MV470WG 470u F, 0.036 Ohms
Css Vishay VJ1206Y123KXXAT 0.012u F
D2 ONSEMI MBR0520 0.385 V
Db ONSEMI MBR0520 0.385 V
L1 Coilcraft DO3316P-332 3.3u H, 0.015 Ohms
M1 Siliconix SI4408DY
M2 Siliconix SI4408DY
Rc1 Vishay CRCW12061183FRT6 118K Ohms
Rc2 Vishay CRCW12061212FRT6 12.12K Ohms
Rfadj Vishay CRCW12068872FRT6 88.7K Ohms
Rfb1 Vishay CRCW12062052FRT6 20.5k Ohms
Rfb2 Vishay CRCW12062212FRT6 22.1K Ohms
Rin Vishay CRCW120610R0FRT6 10 Ohms
U1 National Semiconductor LM2727
rcs Vishay CRCW12062001FRT6

  Design Description

The design uses a LM2727 synchronous controller utilizing external high side and low side N-channel MOSFETs operating at 300kHz. Operating the design at 300Khz aids in having higher efficiency as opposed to operating at higher frequencies. 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


Output Ripple Voltage

Start Up

Switch pin

Transient Load Step