Wavecom GR64 UART Sleep Protocols Dokumentacja Pobierz pdf (Strona 106)

8.3. REGULATOR SELECTION

Figure 8.1: DC rail output of SMPS.

• Adjustment in the size of the inductor - decrease from 260µH to 80µH

to suit the new higher operating frequency.

• Feedback resistor network was adjusted to provide the correct output

voltages of 3.8V and 5.0V.

Figure 8.2 is the schematic of the ﬁnal DC-DC converter to power the

logic circuits. Note that two such circuits are required: one 3.8V unit for the

GSM module as outlined in Section 7.3.1 and a second for the 5V logic. To

further improve the device’s overall eﬃciency, it was decided to provide a soft

switch to disable the 3.8V regulator entirely when the GSM module is not

required. This is prudent, because the GSM unit is not required frequently

and the L4976 draws a quiescent current of 4mA under no-load conditions.

The 5V converter does not have a soft-switch and automatically p owers-up

when the battery has suﬃcient voltage.

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Wavecom GR64 UART Sleep Protocols Dokumentacja Strona 106