Extremely Accurate I
2
C-Integrated
RTC/TCXO/Crystal
Pin Description
PIN
1
2
NAME
32kHz
V
CC
FUNCTION
32kHz Output. This open-drain pin requires an external pullup resistor. When enabled, the output operates
on either power supply. It may be left open if not used.
DC Power Pin for Primary Power Supply. This pin should be decoupled using a 0.1μF to 1.0μF capacitor.
If not used, connect to ground.
Active-Low Interrupt or Square-Wave Output. This open-drain pin requires an external pullup resistor
connected to a supply at 5.5V or less. This multifunction pin is determined by the state of the INTCN bit in
the Control Register (0Eh). When INTCN is set to logic 0, this pin outputs a square wave and its frequency is
determined by RS2 and RS1 bits. When INTCN is set to logic 1, then a match between the timekeeping
registers and either of the alarm registers activates the
INT/SQW
pin (if the alarm is enabled). Because the
INTCN bit is set to logic 1 when power is first applied, the pin defaults to an interrupt output with alarms
disabled. The pullup voltage can be up to 5.5V, regardless of the voltage on V
CC
. If not used, this pin can be
left unconnected.
Active-Low Reset. This pin is an open-drain input/output. It indicates the status of V
CC
relative to the
V
PF
specification. As V
CC
falls below V
PF
, the
RST
pin is driven low. When V
CC
exceeds V
PF
, for t
RST
, the
RST
pin is pulled high by the internal pullup resistor. The active-low, open-drain output is combined with a
debounced pushbutton input function. This pin can be activated by a pushbutton reset request. It has an
internal 50k nominal value pullup resistor to V
CC
. No external pullup resistors should be connected. If the
oscillator is disabled, t
REC
is bypassed and
RST
immediately goes high.
No Connection. Must be connected to ground.
Ground
Backup Power-Supply Input. This pin should be decoupled using a 0.1μF to 1.0μF low-leakage capacitor.
If the I
2
C interface is inactive whenever the device is powered by the V
BAT
input, the decoupling capacitor
is not required. If V
BAT
is not used, connect to ground. UL recognized to ensure against reverse charging
when used with a lithium battery. Go to
www.maxim-ic.com/qa/info/ul.
Serial Data Input/Output. This pin is the data input/output for the I
2
C serial interface. This open-drain pin
requires an external pullup resistor. The pullup voltage can be up to 5.5V, regardless of the voltage on V
CC
.
Serial Clock Input. This pin is the clock input for the I
2
C serial interface and is used to synchronize data
movement on the serial interface. Up to 5.5V can be used for this pin, regardless of the voltage on V
CC
.
DS3231
3
INT/SQW
4
RST
5–12
13
N.C.
GND
14
V
BAT
15
16
SDA
SCL
Detailed Description
The DS3231 is a serial RTC driven by a temperature-
compensated 32kHz crystal oscillator. The TCXO pro-
vides a stable and accurate reference clock, and
maintains the RTC to within ±2 minutes per year accu-
racy from -40°C to +85°C. The TCXO frequency output
is available at the 32kHz pin. The RTC is a low-power
clock/calendar with two programmable time-of-day
alarms and a programmable square-wave output. The
INT/SQW
provides either an interrupt signal due to
alarm conditions or a square-wave output. The clock/cal-
endar provides 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
clock operates in either the 24-hour or 12-hour format
with an
AM/PM
indicator. The internal registers are
accessible though an I
2
C bus interface.
A temperature-compensated voltage reference and
comparator circuit monitors the level of V
CC
to detect
power failures and to automatically switch to the back-
up supply when necessary. The
RST
pin provides an
external pushbutton function and acts as an indicator
of a power-fail event.
Operation
The block diagram shows the main elements of the
DS3231. The eight blocks can be grouped into four
functional groups: TCXO, power control, pushbutton
function, and RTC. Their operations are described sep-
arately in the following sections.
9
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
