DS1371 查看數據表（PDF） - Maxim Integrated

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DS1371

I2C, 32-Bit Binary Counter Watchdog Clock

Maxim Integrated 

DS1371

PIN DESCRIPTION

PIN NAME

FUNCTION

These signals are 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 6pF. No external resistors or capacitors are required. For more

1, 2

X1, X2 information about crystal selection and crystal layout considerations, refer to

Application Note 58: Crystal Considerations with Dallas Real-Time Clocks. The

DS1371 can also be driven by an external 32.768kHz oscillator. In this configuration,

the X1 pin is connected to the external oscillator signal and the X2 pin is floated.

Watchdog Input. A positive edge-triggered hardware interrupt input that restarts the

3

WDS watchdog counter when this signal transitions from a low to a high. While WDS remains

at a static low or high, the watchdog counter continues to decrement.

4

GND Ground

5

SDA

I2C Serial Data. Input/output for I2C data.

6

SCL

I2C Serial Clock. Input for I2C clock.

7

SQW/INT

Square-Wave/Interrupt Output. This pin is used to output the programmable square-

wave or alarm interrupt signal. It is open drain and requires an external pullup resistor.

8

VCC

Supply Voltage Terminal

Detailed Description

The DS1371 is a real-time clock (RTC) with a I2C serial interface that provides elapsed seconds from a

user-defined starting point in a 32-bit counter (Figure 2). A 24-bit counter can be configured as either a

watchdog counter or as an alarm counter. An on-chip oscillator circuit uses a customer-supplied

32.768kHz crystal to keep time.

Oscillator Circuit

The DS1371 uses an external 32.768kHz crystal. The oscillator circuit does not require any external

resistors or capacitors to operate (Figure 2). Table 1 specifies several crystal parameters for the external

crystal. Using a crystal with the specified characteristics, the startup time is usually less than one second.

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

trimmed. Additional error is added by crystal frequency drift caused by temperature shifts. External

circuit noise coupled into the oscillator circuit can result in the clock running fast. Figure 3 shows a

typical PC board layout for isolation of the crystal and oscillator from noise. Refer to Application Note

58: Crystal Considerations with Dallas Real-Time Clocks for detailed information.

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