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The LM2727 evaluation board has been designed for a wide variety of components in order to show the flexibility of the LM2727 chips. The input voltage limitations are the same as the chip: 2.2 VDC to 16 VDC. The regulated output voltage range is from 0.6 V up to 85% of the input voltage. Output current is limited by the components chosen, however, the size of this board and the limitation to SOIC-8 MOSFETs means a realistic limit of about 10 A.
The example design steps 12 V down to 3.3 V at 4 A, with a switching frequency of 800 kHz. This design can be modified by following the Design Considerations section of the LM2727/LM2737 N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages data sheet.
The board is four layers, consisting of signal/power traces on top and bottom, with one internal ground plane and an internal split power plane. All planes are 1-oz. copper, and the board is 62-mil FR4 laminate.
The default circuit that comes with the LM2727 demo board uses a bootstrap diode and small capacitor (D1 and CBOOT) to provide enough gate-to-source voltage on the high-side MOSFET to drive the FET. If a separate rail is available that is more than twice the value of VIN, this higher voltage can be connected directly to the BOOT pin, through the BOOT connector, with a 0.1-µF bypass capacitor, CC. In this case, D1 and CBOOT should be removed from the board. Do not connect both CC and CBOOT/D1 at the same time.
The LM2727 demo board has two extra footprints for dual N-channel MOSFETs in SOIC-8 packages. Footprint Q3 corresponds to devices with footprints such as the Si4816DY "LITTLEFOOT Plus" from Vishay Siliconix. Footprint Q4 corresponds to devices with footprints such as the Si4826DY, also from Vishay Siliconix.