Independent Lcd Supply; Voltage Regulator - ST STM32L152-EVAL Application Note

Power supplies
2.1.2

Independent LCD supply

The V
LCD
two ways:
●
It can receive, from an external circuitry, the desired maximum voltage that is provided
on the segment and common lines to the glass LCD by the microcontroller.
●
It can also be used to connect an external capacitor that is used by the microcontroller
for its voltage step-up converter. This step-up converter is controlled by software to
provide the desired voltage to the segment and common lines of the glass LCD.
The voltage provided to the segment and common lines defines the contrast of the glass
LCD pixels. This contrast can be reduced when the dead time between frames is
configured.
●
When an external power supply is provided to the V
to 3.6 V. It does not depend on V
●
When the LCD is based on the internal step-up converter, the V
connected to a capacitor (see the product datasheets for further information).
2.1.3

Voltage regulator

The internal voltage regulator is always enabled after reset. It can be configured to provide
the core with three different voltage ranges. Choosing a range with low V
consumption but lowers the maximum acceptable core speed. Consumption ranges in
decreasing consumption order are as follows:
●
Range 1, available only for V
●
Range 2 allows CPU frequency up to 16 MHz
●
Range 3 allows CPU frequency up to 4 MHz
Voltage regulator works in three different modes depending on the application modes.
●
In Run mode, the regulator supplies full power to the V
digital peripherals).
●
In Stop mode, Low power run and Low power wait modes, the regulator supplies low
power to the V
●
In Standby mode, the regulator is powered off. The contents of the registers and SRAM
are lost except for those concerned with the Standby circuitry.
8/30
pin is provided to control the contrast of the glass LCD. This pin can be used in
domain, preserving the contents of the registers and SRAM.
core
Doc ID 17496 Rev 5
.
DD
above 2.0 V, allows maximum speed
DD
pin, it should range from 2.5 V
LCD
pin should be
LCD
reduces the
core
domain (core, memories and
core
AN3216