DS1390 Datasheet, PDF (11/24 Pages) Maxim Integrated Products – Low-Voltage SPI/3-Wire RTCs with Trickle Charger

Low-Voltage SPI/3-Wire RTCs with
Trickle Charger
Functional Diagram
X1
X2
V_CC
GND
V_BACKUP
(DS1390/91) CS
(DS1392/93) (CE)
SCLK
(DS1390/91) DIN
(DS1390/91) DOUT
(DS1392/93) I/O
32,768Hz
CRYSTAL
OSCILLATOR
V_CC 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)
RST (DS1391/93)
SQW (DS1392)
ALARM REGISTERS
CONTROL/STATUS
REGISTERS
TRICKLE REGISTER
DS1390/DS1391/
DS1392/DS1393
Detailed Description
The DS1390/DS1391/DS1392/DS1393 RTCs are low-
power clocks/calendars with alarms. Address and data
are transferred serially through a 4-wire SPI interface
for the DS1390 and DS1391 and through a 3-wire inter-
face for the DS1392 and DS1393. The clocks/calendars
provide hundredths of seconds, seconds, minutes,
hours, day, date, month, and year information. The
alarm functions are performed off all timekeeping regis-
ters, 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 correc-
tions for leap year. The clocks operate in either the 24-
hour or 12-hour format with an AM/PM indicator. All four
devices have a built-in temperature-compensated volt-
age reference that detects power failures and automati-
cally 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.
Operation
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 sec-
tion). The devices are fully accessible and data can be
written and read when V_CC is greater than V_PF.
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