DS3232
Extremely Accurate I
2
C RTC with
Integrated Crystal and SRAM
_____________________________________________________________________
9
Pin Description
PIN
NAME
FUNCTION
1, 2,
7–14, 19
N.C.
No Connection. Not connected internally. Must be connected to ground.
3 32kHz
32kHz Push-Pull Output. If disabled with either EN32kHz = 0 or BB32kHz = 0, the state of the 32kHz pin
will be low.
4 V
CC
DC Power Pin for Primary Power Supply. This pin should be decoupled using a 0.1μF to 1.0μF capacitor.
5
INT
/SQW
Active-Low Interrupt or Square-Wave Output. This open-drain pin requires an external pullup resistor. It can
be left open if not used. 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.
6
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 driven high impedance. 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 crystal
oscillator is disabled, t
RST
is bypassed and
RST
immediately goes high.
15 GND
Ground
16 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.maxim-ic.com/qa/info/ul
.
17 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
.
18, 20
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. A connection to only one of the pins is required. The other pin must be
connected to the same signal or be left unconnected. Up to 5.5V can be used for this pin, regardless of the
voltage on V
CC
.
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. Also available are 236 bytes of gen-
eral-purpose battery-backed SRAM.
Operation
The block diagram shows the main elements of the
DS3232. 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.
32kHz TCXO
The temperature sensor, oscillator, and control logic
form the TCXO. The controller reads the output of the
on-chip temperature sensor and uses a lookup table to
determine the capacitance required, adds the aging
correction in AGE register, and then sets the capaci-
tance selection registers. New values, including
changes to the AGE register, are loaded only when a
change in the temperature value occurs. The tempera-
ture is read on initial application of V
CC
and once every
64 seconds (default, see the description for CRATE1
and CRATE0 in the control/status register) afterwards.
