PIN NAME FUNCTION
1 32kHz
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.
2 V
CC
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.
3 INT/SQW
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.
4 RST
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.
5–12 N.C. No Connection. Must be connected to ground.
13 GND Ground
14 V
BAT
Backup Power-Supply Input. When using the device with the V
BAT
input as the primary power source, this
pin should be decoupled using a 0.1μF to 1.0μF low-leakage capacitor. When using the device with the
V
BAT
input as the backup power source, the capacitor is not required. If V
BAT
is not used, connect to ground.
The device is UL recognized to ensure against reverse charging when used with a primary lithium battery.
Go to www.maximintegrated.com/qa/info/ul
.
15 SDA
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
.
16 SCL
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
.
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.
