DS1340-18_03 查看數據表（PDF） - Dallas Semiconductor -> Maxim Integrated

零件编号

产品描述 (功能)

生产厂家

DS1340-18_03

2-Wire RTC with Trickle Charger

Dallas Semiconductor -> Maxim Integrated 

2-Wire RTC with Trickle Charger

Pin Description

PIN

NAME

FUNCTION

1

X1

Connections for a Standard 32.768kHz Quartz Crystal. The internal oscillator circuitry is designed for

operation with a crystal having a specified load capacitance (CL) of 12.5pF. X1 is the input to the

oscillator and can optionally be connected to an external 32.768kHz oscillator. The output of the

2

X2

internal oscillator, X2, is floated if an external oscillator is connected to X1.

Connection for a Secondary Power Supply. For the 1.8V and 3V devices, VBACKUP must be held

3

VBACKUP

between 1.3V and 3.7V for proper operation. VBACKUP can be as high as 5.5V on the 3.3V device.

This pin can be connected to a primary cell such as a lithium coin cell. Additionally, this pin can be

connected to a rechargeable cell or a super cap when used with the trickle-charge feature.

4

GND

Ground

5

SDA

Serial Data Input/Output. SDA is the data input/output for the 2-wire serial interface. The SDA pin is

open drain and requires an external pullup resistor.

6

SCL

Serial Clock Input. SCL is the clock input for the 2-wire interface and is used to synchronize data

movement on the serial interface.

Frequency Test/Output. This pin is used to output either a 512Hz signal or the value of the OUT bit.

When the FT bit is logic 1, the FT/OUT pin toggles at a 512Hz rate. When the FT bit is logic 0, the

7

FT/OUT FT/OUT pin reflects the value of the OUT bit. This open-drain pin requires an external pullup resistor,

and operates with either VCC or VBACKUP applied.

8

VCC

DC Power for Primary Power Supply

Detailed Description

The DS1340 is a low-power clock/calendar with a trickle

charger. Address and data are transferred serially

through a 2-wire bidirectional bus. The clock/calendar

provides seconds, minutes, hours, day, date, month, and

year information. The date at the end of the month is

automatically adjusted for months with fewer than 31

days, including corrections for leap year. The DS1340

has a built-in power-sense circuit that detects power fail-

ures and automatically switches to the backup supply.

Oscillator Circuit

The DS1340 uses an external 32.768kHz crystal. The

oscillator circuit does not require any external resistors

or capacitors to operate. Table 1 specifies several crys-

tal parameters for the external crystal. Figure 3 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.

Clock Accuracy

The initial clock accuracy depends on the accuracy of

the crystal and the accuracy of the match between the

capacitive load of the oscillator circuit and the capaci-

tive load for which the crystal was trimmed. Additional

error is added by crystal frequency drift caused by

Table 1. Crystal Specifications*

PARAMETER SYMBOL MIN TYP MAX UNITS

Nominal

Frequency

fO

32.768

kHz

Series Resistance

ESR

45 kΩ

Load Capacitance

CL

12.5

pF

*The crystal, traces, and crystal input pins should be isolated

from RF generating signals. Refer to Application Note 58:

Crystal Considerations for Dallas Real-Time Clocks for addi-

tional specifications.

RTC

COUNTDOWN

CHAIN

CL1

X1

CL2

X2

RTC

REGISTERS

CRYSTAL

Figure 3. Oscillator Circuit Showing Internal Bias Network

6 _____________________________________________________________________

Share Link: