Power and Clocking
8.7.4I/O 3.3 V Power
A simple LDO linear regulator supplies the 3.3V rail. The Analog Devices ADP3335 is chosen for its very low
•4.1 – 3.8 V zone 10% of the time;
•3.7 – 3.6 V zone at 70% of the time;
•3.5 – 3.4 V at 10% of the time; and
•3.4 – 3.1 V at 10% of the time.
The ADP3335 operates in zone 1,2, 3, and cutoffs in zone 4.
The overall efficiency is:
0.1(3.3/4.0) + 0.7(3.3/3.6) + 0.1(3.3/3.4) = 0.0825 + 0.642 + 0.097 = 0.82
To access the energy in zone 4 use the second LDO linear regulator in a parallel configuration with the ADP3335 and set it to output 3.2 V. Input to this regulator is 5.5 V from the boost converter. When the battery voltage drops below 3.5 V, the ADP3335
8.7.5Peripheral 5.5 V Power
The example form factor reference design provides a 5.5 V rail to supply power to LCD, Audio amplifier and Radio modules. An LT1308A boost converter is used. This device supplies up to 1 A at 5.5 V while operating at 600 kHz with up to 90% efficiency at rated load and 3.6 V input.
In addition, a low battery voltage detect circuit has an
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