component

DS1302 Trickle-Charge RTC

Public Unreviewed

by Ray

Trickle-charge real-time clock with 31 bytes of RAM and a simple 3-wire interface.

rtcreal-time-clocktrickle-charge3-wiretimingadisop-8
Overview Files Discover Packages Releases Dependencies Issues Breadcrumbs Pull Requests Activity

3D Model

Open in new tab ↗

Symbol & Footprint

Schematic Symbol

Open full view ↗

PCB Footprint

Open full view ↗
Contents

README

markdown

DS1302

Analog Devices · Real-Time Clock (RTC) · SOP-8 (208 mil)

The DS1302 is a trickle-charge real-time clock that counts seconds, minutes, hours, date, month, day of week, and year with leap-year compensation. It has 31 bytes of scratchpad RAM and communicates over a simple 3-wire (CE, SCLK, I/O) interface, with an optional trickle charger for a backup capacitor or cell.

Pinout

Pin Name Type Function
1 VCC2 power_in Primary power-supply pin in dual-supply configuration. The DS1302 operates from the larger of VCC1 or VCC2. When VCC2 is greater than VCC1 + 0.2V, VCC2 powers the DS1302; when VCC2 is less than VCC1, VCC1 powers the DS1302. Operating range 2.0V to 5.5V.
2 X1 passive Connection for a standard 32.768kHz quartz crystal. Internal oscillator is designed for a crystal with 6pF specified load capacitance. Can also be driven by an external 32.768kHz oscillator applied to X1 (with X2 floated).
3 X2 passive Second connection for the 32.768kHz quartz crystal. Left floating when an external oscillator drives X1.
4 GND power_in Device ground.
5 CE input Chip enable input. CE must be asserted high during a read or write to enable the control logic and shift register access. Has an internal 40k-ohm (typ) pulldown to ground. Previous datasheet revisions referred to this pin as /RST; functionality is unchanged.
6 I/O bidirectional Bidirectional serial data pin for the 3-wire interface. Push-pull output during read, high-impedance when CE is low, tri-stated on rising edge of SCLK. Has an internal 40k-ohm (typ) pulldown to ground.
7 SCLK input Serial clock input used to synchronize data movement on the 3-wire serial interface. Has an internal 40k-ohm (typ) pulldown to ground.
8 VCC1 power_in Low-power/battery-backup supply pin. In systems using the trickle charger the rechargeable energy source (e.g. supercap or lithium cell) is connected to this pin. UL-recognized reverse-charging protection is required when used with a lithium battery.

Key specifications

Parameter Value
Type Real-time clock (RTC)
Interface 3-wire (CE, SCLK, I/O)
Timekeeping Seconds to year, leap-year compensated to 2100
RAM 31 bytes scratchpad
Backup Trickle-charge circuit for cap/cell
Supply voltage 2.0 V to 5.5 V
Operating temperature -40 C to 85 C

Ordering variants

Same part, different packaging or reel option.

  • DS1302+
  • DS1302N+
  • DS1302S+
  • DS1302SN+
  • DS1302Z+
  • DS1302ZN+

CAD (KiCad official)

  • Symbol: ds1302.kicad_sym
  • Footprint: ds1302.kicad_mod
  • 3D model: SOP-8 208 mil (wide) body from KiCad Package_SO/SOIC-8_5.3x5.3mm_P1.27mm.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

  • Datasheet: Analog Devices datasheet (13 pp, sha256 fb627b436b89e8c9, retrieved 2026-08-17, tier: manufacturer)
  • Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
  • CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF