AN2419 datasheet(4/22 Pages) STMICROELECTRONICS

4 / 22 page

Power supplies

AN2419

4/22

Power supplies

1.1

Introduction

The device has five power pins:

●

VDD_IO: power supply for I/Os (3.3V ±0.3V or 5V ±0.5V). Must be kept on, even in

STANDBY mode.

●

V18 (pins V18REG and V18 which are internally shorted): Power Supply for Digital,

SRAM and Flash: 1.8V ± 0.15V.

●

V18_BKP: Backup Power Supply for STANDBY or STOP Mode

Two embedded regulators are available to supply the internal 1.8V digital power:

V18 and V18_BKP are normally generated internally by these regulators.

The Main Voltage Regulator (MVREG) supplies V18 and V18_BKP. It delivers a power supply

of 1.8V ± 0.15V.

The Low Power Voltage Regulator (LPVREG) can supply V18_BKP or V18 in STOP or

STANDBY mode. It delivers a power supply of around 1.4V.

Two sensitive analog blocks have dedicated power pins:

●

VDDA_PLL: Analog Power supply for PLL (must have the same voltage level as VDD_IO)

●

VDDA_ADC: Analog Power supply for ADC (must have the same voltage level as VDD_IO)

1.2

Power supply schemes

The device can be connected in any of the following configurations depending on your

application requirements:

●

Power Scheme 1: Single external 3.3V power source

●

Power Scheme 2: Dual external 3.3V and 1.8V power sources

●

Power Scheme 3: Single external 5.0V power source

●

Power Scheme 4: Dual external 5.0V and 1.8V power sources

1.2.1

Power scheme 1: single external 3.3V power source

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

VREG_DIS pin to low level.

●

The V18REG pin must be connected to external stabilization capacitors (min. 10 uF

Tantalum, low series resistance).

●

The V18 pin must be connected to external stabilization capacitors (33nF ceramic).

●

The V18_BKP pin must be connected to an external stabilization capacitor of 1µF.

●

A decoupling capacitor of 1µF must be added on the VDD_IO pin which is closest to the

V18REG pin.

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