STM32L021D4 datasheet(26/114 Pages) STMICROELECTRONICS

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Functional overview

STM32L021x4

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DocID027982 Rev 5

3.10

Analog-to-digital converter (ADC)

A native 12-bit, extended to 16-bit through hardware oversampling, analog-to-digital

converter is embedded into STM32L021x4 devices. It has up to 10 external channels and 2

internal channels (temperature sensor, voltage reference). Three channels, PA0, PA4 and

PA5, are fast channels, while the others are standard channels.

The ADC performs conversions in single-shot or scan mode. In scan mode, automatic

conversion is performed on a selected group of analog inputs.

The ADC frequency is independent from the CPU frequency, allowing maximum sampling

rate of 1.14 MSPS even with a low CPU speed. The ADC consumption is low at all

frequencies (~25 µA at 10 kSPS, ~200 µA at 1MSPS). An auto-shutdown function

guarantees that the ADC is powered off except during the active conversion phase.

The ADC can be served by the DMA controller. It can operate from a supply voltage down to

1.65 V.

The ADC features a hardware oversampler up to 256 samples, this improves the resolution

to 16 bits (see AN2668).

An analog watchdog feature allows very precise monitoring of the converted voltage of one,

some or all scanned channels. An interrupt is generated when the converted voltage is

outside the programmed thresholds.

The events generated by the general-purpose timers (TIMx) can be internally connected to

the ADC start triggers, to allow the application to synchronize A/D conversions and timers.

3.11

Temperature sensor

The temperature sensor (TSENSE) generates a voltage VSENSE that varies linearly with

temperature.

The temperature sensor is internally connected to the ADC_IN18 input channel which is

used to convert the sensor output voltage into a digital value.

The sensor provides good linearity but it has to be calibrated to obtain good overall

accuracy of the temperature measurement. As the offset of the temperature sensor varies

from chip to chip due to process variation, the uncalibrated internal temperature sensor is

suitable for applications that detect temperature changes only.

To improve the accuracy of the temperature sensor measurement, each device is

individually factory-calibrated by ST. The temperature sensor factory calibration data are

stored by ST in the system memory area, accessible in read-only mode (see Table 56:

Temperature sensor calibration values).

3.11.1

Internal voltage reference (VREFINT)

The internal voltage reference (VREFINT) provides a stable (bandgap) voltage output for the

ADC and Comparators. VREFINT is internally connected to the ADC_IN17 input channel. It

enables accurate monitoring of the VDD value (since no external voltage, VREF+, is available

for ADC). The precise voltage of VREFINT is individually measured for each part by ST during

production test and stored in the system memory area (see Table 19: Embedded internal

reference voltage calibration values). It is accessible in read-only mode.

STM32L021D4 Datenblatt(PDF) 26 Page - STMicroelectronics

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