AN1759 datasheet(3/24 Pages) FREESCALE

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Application Note

DS1307 Hardware Interface

AN1759

The DS1307 has built-in power management circuitry to detect power

failures on the VDD pin and when detected will switch power over to the

battery back-up pin, VBAT. Access to the device is terminated when VDD

falls below 1.25 x VBAT. Further accesses to the device are not allowed.

On power up, the device switches power from VBAT to VDD when the VDD

pin is 0.2 volts above VBAT. Once VDD is higher than 1.25 x VBAT, normal

operations can continue.

Address and data are communicated via the 2-wire bus. The DS1307

operates as a slave at all times and is accessed by first transmitting the

DS1307’s identification code on the bus.

DS1307 Hardware Interface

Pinout and Pin

Descriptions

Figure 1. DS1307 Pinout

VDD and GND

These pins serve as the main power source for the device. When

+5 volts is applied to this pin, the device is fully accessible and data can

be read or written. If the power on the VDD pin falls below 1.25 x VDD, the

device switches its power supply to VBAT. At this point, reading and

writing to the device is prohibited. The timekeeping function and non-

volatile RAM are unaffected.

VBAT

This pin is the power input for any standard 3-volt lithium battery or other

3-volt source. For proper operation, this voltage must be held between

2.5 and 3.5 volts. A lithium battery with at least a 35-mA hours rating will

back up the DS1307 for more than 10 years in the absence of power.

VBAT

GND

SQW/OUT

SCL

SDA

VDD

Freescale Semiconductor, Inc.

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Go to: www.freescale.com

AN1759 Datasheet(PDF) 3 Page - Freescale Semiconductor, Inc