AN2476 datasheet(9/49 Pages) STMICROELECTRONICS

9 / 49 page

AN2476

Power supply and clocks

9/49

1.3.4

Power scheme 4: dual external 5.0V 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 and providing 5V I/O

capability. V18 and V18_BKP are provided externally through the V18REG, V18 and V18_BKP

power pins.

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

Power Voltage Regulator.

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

1.8V power supply source. Internally, VCORE and VBACKUP are also shorted by the power

switch shown in Figure 6: Power supply scheme 4 (5V and 1.8V supplies, VREGDIS=1) on

page 9.

In this scheme:

●

STANDBY mode is not available

●

USB functionality is not available

Figure 6.

Power supply scheme 4 (5V and 1.8V supplies, VREGDIS=1)

5.0V

MAIN

VOLTAGE

LOW POWER

VOLTAGE

GP I/Os

OUT

ADC

ADCIN

+/-0.5V

VIO=5.0V

VDD_ADC

VSS_ADC

PLL

5.0V

VSS_PLL

VSS_IO

VDD_IO

VDD_PLL

REGULATOR

OFF

I/O LOGIC

OFF

KERNEL

BACKUP

(CORE &

DIGITAL &

(OSC32K, RTC

MEMORIES)

CIRCUITRY

WAKEUP LOGIC,

BACKUP REGISTERS)

POWER

SWITCH

VCORE

VBACKUP

V18_BKP

V18REG

VSS_BKP

VREG_DIS

1.8V

VSS18

VDD_IO

V18

REGULATOR

NOTE : THE EXTERNAL 5.0V POWER SUPPLY MUST ALWAYS BE KEPT ON

VMVREG

VLPVREG

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