AN3216 datasheet(11/33 Pages) STMICROELECTRONICS

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AN3216

Power supplies

Figure 3. Optional LCD power supply scheme

•

Option 1: LCD power supply is provided by a dedicated VLCD supply source, VSEL

switch is open.

•

Option 2: LCD power supply is provided by the internal step-up converter, VSEL switch

is closed, an external capacitance is needed for correct behavior of this converter.

Note:

The availability of the VLCD rails depend on the device; please refer to your product

datasheet for more details.

2.3

Reset and power supply supervisor

The input supply to the main and low power regulators is monitored by a power-on/power-

down/brownout reset circuit. Power-on/power-down reset are a null power monitoring with

fixed threshold voltages, whereas brownout reset gives the choice between several

thresholds with a very low, but not null, power consumption.

In addition, the STM32L1xxx embeds a programmable voltage detector that compares the

power supply with the programmable threshold. An interrupt can be generated when the

power supply drops below the VPVD threshold and/or when the power supply is higher than

the VPVD threshold. The interrupt service routine then generates a warning message and/or

puts the MCU into a safe state.

MSv32511V1

VDD1/2/.../N

N x 100 nF

+ 1 x 10 μF

Step-up

converter

VSS1/2/.../N

VDD

100 nF

VLCD

VLCDrail1

VLCDrail2

VLCDrail3

VLCD

PB0 or PE12

PB2

PB12 or PE11

CEXT

Crail3

LCD

VSEL

Crail2

Crail1

Option 1

Option 2

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