# DS3231 real-time clock: specs and pinout

> I2C real-time clock with an integrated temperature-compensated crystal oscillator and a battery backup input.

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I2C real-time clock with an integrated temperature-compensated crystal oscillator and a battery backup input.

Every value cites its sourceChip-level pinout

[Buy on Compoden](https://compoden.com/products/ds3231-real-time-clock-module-i2c-rtc-with-battery-backup)

## Specs

| Spec | Value | Source |
|---|---|---|
| Supply voltage VCC | 2.3 V to 5.5 V (3.3 V typ) | source Electrical Characteristics, Supply Voltage (p.2) |
| Backup supply VBAT | 2.3 V to 5.5 V | source Electrical Characteristics, timekeeping battery (p.3) |
| Active supply current ICCA | 200 uA (VCC = 3.63 V) | source Electrical Characteristics, Active Supply Current (p.2) |
| Accuracy 0 C to +40 C | +/-2 ppm | source Features (p.1) |
| Accuracy -40 C to +85 C | +/-3.5 ppm | source Features (p.1) |
| I2C mode and speed | Fast mode, 400 kHz | source Features (p.1) |
| I2C slave address | 1101000 (binary) | source Slave address in I2C read/write sequence (p.16) |
| Temperature range (industrial) | -40 C to +85 C | source Features (p.1); Absolute Maximum Ratings (p.2) |

## Power

| | Value | Source |
|---|---|---|
| Supply | VCC 2.3-5.5 V; VBAT 2.3-5.5 V (chip ratings) | source Electrical Characteristics (p.2) |
| Current | ICCA 200 uA (VCC = 3.63 V, as listed) | source Electrical Characteristics (p.2) |

## Chip pins

These are the pins of the chip on the module, from the chip datasheet. The module's own header may label or expose them differently. Module header labels come from the Compoden listing, not an official module schematic.

| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| VCC | DC power pin for primary power supply | 2.3-5.5 V (3.3 V typ) | Datasheet decouples with 0.1-1.0 uF. | source Pin Description (p.9); Recommended Operating Conditions (p.2) |
| GND | Ground | 0 V | | source Pin Description (p.9) |
| VBAT | Backup power-supply input | 2.3-5.5 V (3.0 V typ) | If VBAT is not used, connect to ground. Module battery/charging circuit is not in the datasheet. | source Pin Description (p.9); Recommended Operating Conditions (p.2) |
| SDA | Serial data input/output (I2C), open-drain, needs an external pullup | Pullup voltage up to 5.5 V regardless of VCC; any-pin absolute max -0.3 to +6.0 V | | source Pin Description (p.9); Absolute Maximum Ratings |
| SCL | Serial clock input (I2C) | Up to 5.5 V can be used regardless of VCC; any-pin absolute max -0.3 to +6.0 V | | source Pin Description (p.9); Absolute Maximum Ratings |
| INT/SQW | Active-low interrupt or square-wave output; open-drain, needs external pullup | Pullup up to 5.5 V regardless of VCC | If not used, leave unconnected. | source Pin Description (p.9) |
| 32kHz | 32 kHz output, open-drain, needs external pullup | | May be left open if not used. | source Pin Description (p.9) |
| RST | Active-low reset, open-drain input/output with internal 50 k pullup to VCC | | Datasheet: no external pullup should be connected. | source Pin Description (p.9) |

## Common mistakes

- Expecting +/-2 ppm at every temperature: +/-2 ppm applies from 0 C to +40 C; the industrial limit is +/-3.5 ppm from -40 C to +85 C ([source](https://www.analog.com/media/en/technical-documentation/data-sheets/ds3231.pdf))
- Running VCC below 2.3 V: the supply range is 2.3-5.5 V, and VBAT must also stay within 2.3-5.5 V for backup ([source](https://www.analog.com/media/en/technical-documentation/data-sheets/ds3231.pdf))
- Assuming a different I2C address: the device address is 1101000 ([source](https://www.analog.com/media/en/technical-documentation/data-sheets/ds3231.pdf))

## What we could not confirm

- Battery charging and CR2032 suitability are module-level claims; not in the datasheet.
- Module-level supply (3.3-5 V board) not in datasheet.
- Accuracy at 3.3 V vs other supply voltages is not restated here; check the datasheet tables.
- ICCA 200 uA: the datasheet table column is ambiguous; confirm whether this is max or typical.
- Pin rows are the DS3231 chip pins; the 4-pin module header (listing: VCC, GND, SDA, SCL) is third-party and unsourced; 32kHz, SQW and RST may or may not be broken out.
- Module pull-up values and any CR2032 charging resistor are board facts, not in the datasheet.

## Sources

- [link](https://www.analog.com/media/en/technical-documentation/data-sheets/ds3231.pdf) (Maxim/ADI DS3231 Rev 10, 3/15)
- Copy of the Maxim datasheet hosted by a hosted copy: [link](https://cdn-shop.adafruit.com/product-files/3013/DS3231.pdf)

Building with the DS3231 real-time clock? [Describe your project on Soldr](https://app.soldr.ai): it assigns pins from the board's published pinout, checks power and logic levels, and shows how to wire every part.