Based on the feedback of the sckematic of the master and slave board circuit. we deicde to change the power circuit suggested by Prof Adrain. It is because the design consumes more energy in the voltage conversion.
By recheck the database of farnell, we decide to use TPS61130 which can give two different voltage level supplies.

The main features of TPS61130 are:

·         Synchronous, up to 90% efficient, SEPIC Converter with 300mA Output Current form 2.5 V input.

·         Integrated 200 mA Reverse Voltages protected LDO for DC/DC output voltage post regulation or second output voltage.

·         40 µA(Typical) quiescent current

·         Input voltage range: 1.8 V to 5.5 V

·         Power save mode for improved efficiency at low output power

·         Low battery comparator

·         Power good output

·         Low EMI-converter (integrated antiringing switch)

·         Load disconnect during shutdown

·         Overtemperature protection

·         Available in a small 4mmx4mm QFN-16 or in a TSSOP-16 package

As the circuit schematic has been fixed, we start to route the physical circuit to make the real testing.