https://github.com/chrisb2/ds3231-breakout

Low Current RTC Breakout With Super Capacitor Backup
https://github.com/chrisb2/ds3231-breakout

backup breakout ds3231 real-time-clock rtc supercapacitor

Last synced: 3 months ago
JSON representation

Low Current RTC Breakout With Super Capacitor Backup

• Host: GitHub
• URL: https://github.com/chrisb2/ds3231-breakout
• Owner: chrisb2
• License: mit
• Created: 2021-09-25T06:02:41.000Z (over 4 years ago)
• Default Branch: main
• Last Pushed: 2021-09-25T21:12:39.000Z (over 4 years ago)
• Last Synced: 2026-01-05T02:35:12.473Z (5 months ago)
• Topics: backup, breakout, ds3231, real-time-clock, rtc, supercapacitor
• Homepage:
• Size: 1.5 MB
• Stars: 3
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE.md

Awesome Lists containing this project

README

          
# Low Current RTC Breakout With Super Capacitor Backup



This 32x21mm breakout is based on the [DS3231](docs/DS3231.pdf) Real Time Clock (RTC) from Maxim Integrated and a [FT0H474ZF](docs/FT0H474ZF.pdf) 0.47F super capacitor from Kemet for backup power.

The design powers the DS3231 via the Vbat input rather than Vcc, this results in a current consumption of ~3uA, with spikes to 575uA every 65 seconds when temperature conversion occurs. See the electrical characteristics for Vcc = 0V, Vbat = 2.3V to 5.5V on page 3 of the data sheet.

## Design Information

![Schematic](rtc-ds3231-schematic.png)

* The schematic shows a DS3231SN which operates accurately below freezing, but the DS3131S can be used if the device is used at room temperature.

* The [BAT54H](docs/BAT54H.pdf) Schottky diode prevents the super capacitor from powering the connected MCU. It has a forward current of 200mA to allow for the current to charge the super capacitor.

* R3 has been chosen to limit the super capacitor charge current to ~150mA based on Vbat being 3.3V. If the input voltage is higher a correspondingly larger value will be required to maintain the maximum current of 150mA.

## PCB

The design files can be found at [https://oshwlab.com/chrisb2/ds3231-low-power](https://oshwlab.com/chrisb2/ds3231-low-power) and the Gerbers are included in this repository.

![PCB](rtc-ds3231-pcb.png)

## BOM

| Designator | Value | Part |

|------|-------|----------|

| - | DS3231SN | 1 |

| C1 | FT0H474ZF 0.47F | 1 |

| C2 | 0.1uF | 1 |

| R1/R2 | 4.7k | 2 |

| R3 | 15 (500mW) | 1|

| D1 | BAT54H | 1|