AN2419 datasheet(5/22 Pages) STMICROELECTRONICS

5 / 22 page

AN2419

Power supplies

5/22

Figure 1.

Power supply scheme 1 (single 3.3V supply

, VREGDIS=0) in NORMAL mode

1.2.2

Power scheme 2: dual external 3.3V and 1.8V power sources

In this configuration, the internal voltage regulators are switched off by forcing the

VREG_DIS pin to high level. This scheme has the advantage of saving power consumption

when the 1.8V power supply is already available in the application. V18 and V18_BKP are

provided externally through the V18REG, V18 and V18_BKP power pins.

●

The external 3.3V power supply must always be kept on.

●

VREG_DIS pin is tied to high level which disables the Main Voltage Regulator and

the Low Power Voltage Regulator.

Caution:

When powered by 5.0V, the USB peripheral cannot operate.

●

All digital power pins (V18REG, V18 and V18_BKP) must be externally shorted to the

same 1.8V power supply source.

●

In this scheme, STANDBY Mode is not available.

V18_BKP

VDD_ADC

VSS_ADC

VSS_PLL

VSS_IO

VDD_IO

V18REG

VDD_PLL

VSS18

VSS_BKP

VREG_DIS

V18

1µF

VSS18

STR750

33nF

10µF

+3.3V

1µF

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