DS1390_09 Datasheet, PDF(12/26 Page) Maxim Integrated Products – Low-Voltage SPI/3-Wire RTCs with Trickle Charger

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DS1390_09 Datasheet, PDF (12/26 Pages) Maxim Integrated Products – Low-Voltage SPI/3-Wire RTCs with Trickle Charger

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Low-Voltage SPI/3-Wire RTCs with

Trickle Charger

Functional Diagram

VCC

GND

VBACKUP

(DS1390/91/94) CS

(DS1392/93) (CE)

SCLK

(DS1390/91/94) DIN

(DS1390/91/94) DOUT

(DS1392/93) I/O

VCC LEVEL DETECT,

POWER SWITCH,

WRITE PROTECT,

TRICKLE CHARGER

BUS

INTERFACE

HUNDREDTHS-OF-

SECONDS

GENERATOR

REAL-TIME CLOCK

WITH HUNDREDTHS

OF SECONDS

SQUARE-WAVE RATE

SELECTOR, INT, MUX,

RST OUTPUT

SQW/INT (DS1390/93/94)

RST (DS1391)

SQW (DS1392)

ALARM REGISTERS

CONTROL/STATUS

REGISTERS

TRICKLE REGISTER

DS1390/DS1391/

DS1392/DS1393/DS1394

Detailed Description

The DS1390âDS1394 RTCs are low-power clocks/calen-

dars with alarms. Address and data are transferred seri-

ally through a 4-wire SPI interface for the DS1390 and

DS1391 and through a 3-wire interface for the DS1392,

DS1393, and DS1394. The DS1390/DS1391 operate as a

slave device on the SPI serial bus. The DS1392/DS1393

operate using a 3-wire synchronous serial bus. Access is

obtained by selecting the part by the CS pin (CE on

DS1392/DS1393) and clocking data into/out of the part

using the SCLK and DIN/DOUT pins (I/O on

DS1392/DS1393). Multiple-byte transfers are supported

within one CS low period (see the SPI Serial-Data Bus

section). The clocks/calendars provide hundredths of

seconds, seconds, minutes, hours, day, date, month,

and year information. The alarm functions are performed

off all timekeeping registers, allowing the user to set high

resolution alarms. The date at the end of the month is

automatically adjusted for months with fewer than 31

days, including corrections for leap year. The clocks

operate in either the 24-hour or 12-hour format with an

AM/PM indicator. All five devices have a built-in tempera-

ture-compensated voltage reference that detects power

failures and automatically switches to the battery supply.

Additionally, the devices can provide trickle charging of

the backup voltage source, with selectable charging

resistance and diode voltage drops.

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