DS1672(2011) View Datasheet(PDF) - Maxim Integrated

Part Name

Description

MFG CO.

DS1672
(Rev.:2011)

I2C 32-Bit Binary Counter RTC

Maxim Integrated 

DS1672

Detailed Description

The DS1672 provides a 32-bit counter that increments once-per-second. The counter data is accessible

via an I2C serial interface. A precision, temperature-compensated, voltage reference and comparator

circuit monitors VCC. When VCC drops below VPF, RST becomes active and the interface is disabled to

prevent data corruption. The device switches to the backup supply input, which maintains oscillator and

counter operation while VCC is absent. When VCC rises above VPF, RST remains low for a period of time

(tRPU) to allow VCC to stabilize.

The block diagram in Figure 4 shows the main elements of the DS1672. As shown, communications to

and from the DS1672 occur serially over a I2C, bidirectional bus. The DS1672 operates as a slave device

on the I2C bus. Access is obtained by implementing a START condition and providing a device

identification code followed by a register address. Subsequent registers can be accessed sequentially until

a STOP condition is executed.

Figure 4. Block Diagram

X1

X2

Oscillator

CL

CL

and

divider

VCC

VBACKUP

GND

RST

N

Power Control

SCL

SDA

I2C Interface

1Hz

32-Bit Counter

(4 Bytes)

Control

Trickle Charger

Control Logic

Address Register

Dallas

Semiconductor

DS1672

Oscillator Circuit

The DS1672 uses an external 32.768kHz crystal. The oscillator circuit does not require any external

resistors or capacitors to operate. Table 1 specifies several crystal parameters for the external crystal.

Figure 4 shows a functional schematic of the oscillator circuit. If using a crystal with the specified

characteristics, the startup time is usually less than one second.

Table 1. Crystal Specifications*

PARAMETER

SYMBOL

MIN

TYP

MAX UNITS NOTES

Nominal Frequency

FO

32.768

kHz

Series Resistance

ESR

45

kΩ

Load Capacitance

CL

6

pF

* The crystal, traces, and crystal input pins should be isolated from RF generating signals. Refer to Application Note 58:

Clock Accuracy

The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match

between the capacitive load of the oscillator circuit and the capacitive load for which the crystal was

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