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

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DS1340

I2C RTC with Trickle Charger

Dallas Semiconductor -> Maxim Integrated 

I2C RTC with Trickle Charger

Pin Description

PIN

8 16

1—

2—

3 14

4 15

5 16

61

72

83

— 4–13

NAME

X1

X2

VBACKUP

GND

SDA

SCL

FT/OUT

VCC

N.C.

FUNCTION

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 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

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. UL

recognized to ensure against reverse charging when used with a lithium battery.

Ground

Serial Data Input/Output. SDA is the data input/output for the I2C serial interface. The SDA pin is open

drain and requires an external pullup resistor.

Serial Clock Input. SCL is the clock input for the I2C 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 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.

DC Power for Primary Power Supply

No Connection. Must be connected to ground.

Detailed Description

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

charger. Address and data are transferred serially

through a I2C bidirectional bus. The clock/calendar pro-

vides 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

Table 1. Crystal Specifications*

PARAMETER SYMBOL MIN TYP MAX UNITS

Nominal

Frequency

fO

32.768

kHz

Series Resistance

ESR

Load Capacitance

CL

45,60** kΩ

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.

**A crystal with up to 60kΩ ESR can be used if the minimum

operating voltages on both VCC and VBACKUP are at least 2.0V.

RTC

COUNTDOWN

CHAIN

CL1

CL2

RTC

REGISTERS

X1

X2

CRYSTAL

Figure 3. Oscillator Circuit Showing Internal Bias Network

6 _____________________________________________________________________

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