STM32L021D4 datasheet(21/114 Pages) STMICROELECTRONICS

21 / 114 page

DocID027982 Rev 5

21/114

STM32L021x4

Functional overview

Five BOR thresholds are available through option bytes, starting from 1.8 V to 3 V. To

reduce the power consumption in Stop mode, it is possible to automatically switch off the

internal reference voltage (VREFINT) in Stop mode. The device remains in reset mode when

VDD is below a specified threshold, VPOR/PDR or VBOR, without the need for any external

reset circuit.

Note:

The start-up time at power-on is typically 3.3 ms when BOR is active at power-up, the start-

up time at power-on can be decreased down to 1 ms typically for devices with BOR inactive

at power-up.

The devices feature an embedded programmable voltage detector (PVD) that monitors the

VDD/VDDA power supply and compares it to the VPVD threshold. This PVD offers 7 different

levels between 1.85 V and 3.05 V, chosen by software, with a step around 200 mV. An

interrupt can be generated when VDD/VDDA drops below the VPVD threshold and/or when

VDD/VDDA is higher than the VPVD threshold. The interrupt service routine can then generate

a warning message and/or put the MCU into a safe state. The PVD is enabled by software.

3.4.3

Voltage regulator

The regulator has three operation modes: main (MR), low power (LPR) and power down.

•

MR is used in Run mode (nominal regulation)

•

LPR is used in the Low-power run, Low-power sleep and Stop modes

•

Power down is used in Standby mode. The regulator output is high impedance, the

kernel circuitry is powered down, inducing zero consumption but the contents of the

registers and RAM are lost except for the standby circuitry (wakeup logic, IWDG, RTC,

LSI, LSE crystal 32 KHz oscillator, RCC_CSR).

3.4.4

Boot modes

At startup, BOOT0 pin and nBOOT0, nBOOT1 and nBOOT_SEL option bits are used to

select one of three boot options:

•

Boot from Flash memory

•

Boot from System memory

•

Boot from embedded RAM

The bootloader is located in System memory. It is used to reprogram the Flash memory by

using SPI1 (PA4, PA7, PA13 and PA14 on TSSOP14 package or PA4, PA5, PA6 and PA7

on other packages) or USART2 (PA2, PA3 and PA9, PA10).

If the bootloader is activated (the bootloader is active on all empty devices due to the empty

check mechanism), then the above mentioned bits are configured depending on whether

SPI1 or USART2 functionality is used.

See STM32™ microcontroller system memory boot mode AN2606 for details.

STM32L021D4 数据表(PDF) 21 Page - STMicroelectronics

STM32L021D4 数据表(HTML) 21 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载