RTC

USE STM Internal RTC	https://embedded-lab.com/blog/stm32s-internal-rtc/
Atmel RTC calibration appnote	https://ww1.microchip.com/downloads/en/Appnotes/Atmel-42251-RTC-Calibration-and-Compensation_AP-Note_AT03155.pdf
TR8804	TKD	1.65-5.5V	I2C	int xtal	link
RV-3032-C7	Micro-Crystal	2.5ppm	-40…+85C	1.98$ (при заказе 3000 шт.)	1.3-5.5V	I2C	int xtal	link
INS5101A	DaPu	I2C	SOIC8
INS5699C	DaPu	3.4ppm	-40…+85C	1.49$ (при заказе 3000 шт.)	1.6-5.5V	I2C	TCXO	SMD3225
INS5699S	DaPu	5ppm	-40…+85C	1.298$ (при заказе 3000 шт.)	2.5-5.5V	I2C	TCXO	SMD3225
DS1302Z	JSMICRO	300nA	31×8	0…+70C	2-5.5V	3WIRE (SPI)	SOIC8	trickle-charger	link
DS1307ZM/TR	HGSEMI	500nA	56×8	5V	I2C	SOIC8
PCF8523TK/1,118	NXP	150nA	I2C
DS3231MZ+	Maxim	5ppm	I2C	SOIC8
BL5372	Belling	400nA	-	-40…+85C	1.8-5.5V	I2C	SOIC8	link

Схемотехника

Калибровка

ICs

BL5372

BL5372 - аналог Dallas DS1337, однако I2C обмен отличается ???

PCF8523TK/1,118

Clock operating voltage: 1.0 V to 5.5 V

Vth(sw)bat is the battery switch threshold voltage. Typical value is 2.5 V.

When VBAT drops below the threshold value Vth(bat)low (typically 2.5 V), the BLF flag (register Control_3) is set to indicate that the battery is low and that it must be replaced.

VBAT battery supply voltage power management function active 1.8 - 5.5 V

Vth(sw)bat battery switch threshold voltage 2.1 2.5 2.7 V