Low-Voltage SPI/3-Wire RTCs with

Trickle Charger

10

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Pin Description

PIN

DS1390

DS1391

DS1392

DS1393

NAME

FUNCTION

111

1

X1

222

2

X2

Connections for Standard 32.768kHz Quartz Crystal. The internal oscillator

circuitry is designed for operation with a crystal having a 6pF specified load

connected to an external 32.768kHz oscillator. The output of the internal

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

333

3

DC Backup Power Input for Primary Cell. This pin is a rechargeable

battery/super cap or a secondary supply. UL recognized to ensure against

reverse charging current when used with a lithium battery.

44

—

—

CS

SPI Chip-Select Input. This pin is used to select or deselect the part.

——

44

CE

Chip Enable for 3-Wire Interface

555

5

GND

Ground

66

——

DIN

SPI Data Input. This pin is used to shift address and data into the part.

——

6

—

INT

Interrupt Output. This pin is used to output the interrupt signal, if enabled by

the control register. The maximum voltage on this pin is 5.5V, independent

—9

—

6

RST

This pin is combined with a debounced pushbutton input function. This pin

can be activated by a pushbutton reset request. This pin has an internal,

50k

connected. If the crystal oscillator is disabled, the startup time of the

77

—

—

DOUT

SPI Data Output. Data is output on this pin when the part is in read mode.

CMOS push-pull driver.

——

77

I/O

Input/Output for 3-Wire Interface. CMOS push-pull driver.

888

8

SCLK

Serial Clock Input. This pin is used to control the timing of data into and out

of the part.

9—

—

9

SQW/INT

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

square wave or interrupt signal. When enabled by setting the ESQW bit to

logic 1, the SQW/INT pin outputs one of four frequencies: 32.768kHz,

8.192kHz, 4.096kHz, or 1Hz. This pin is open drain and requires an external

pullup resistor. The maximum voltage on this pin is 5.5V, independent of

——

9

—

SQW

Square-Wave Output. This pin is open drain and requires an external pullup

10

10

10

10

DC Power Pin for Primary Power Supply