DS3234S# Maxim Integrated Products, DS3234S# Datasheet - Page 10

• Manufacturer Part Number: DS3234S#
• Description: IC RTC W/TCXO 20-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Clock/Calendar/TCXO/Crystalr

Specifications of DS3234S#

• Memory Size: 2K (256 x 8)
• Time Format: HH:MM:SS (12/24 hr)
• Date Format: YY-MM-DD-dd
• Interface: SPI, 3-Wire Serial
• Voltage - Supply: 2 V ~ 5.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (7.5mm Width)
• Function: Clock/Calendar/Alarm/Battery Backup/Interrupt
• Rtc Memory Size: 256 Byte
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 2 V
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Mounting Style: SMD/SMT
• Rtc Bus Interface: Serial (4-Wire, SPI)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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 for-
mat with AM/PM indicator. Access to the internal regis-
ters is possible through an SPI bus interface.
A temperature-compensated voltage reference and
comparator circuit monitors the level of V
power failures and to automatically switch to the backup
supply when necessary. When operating from the back-
up supply, access is inhibited to minimize supply cur-
rent. Oscillator, time and date, and TCXO operations can
continue while the backup supply powers the device.
The RST pin provides an external pushbutton function
and acts as an indicator of a power-fail event.
The block diagram shows the main elements of the
DS3234. 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.
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 the AGE register, and then sets the
capacitance 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
64 seconds (default, see the description for CRATE1
and CRATE0 in the Control/Status Register section)
afterwards.
The power control function is provided by a tempera-
ture-compensated voltage reference and a comparator
circuit that monitors the V
accessible and data can be written and read when V
is greater than V
both V
blocked from any access. If V
device power is switched from V
drops below V
device power is switched from V
drops below V
and V
goes high (Table 1).
To preserve the battery, the first time V
the device, the oscillator does not start up until V
Extremely Accurate SPI Bus RTC with
Integrated Crystal and SRAM
10
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BAT
PF
, read and write access is allowed after RST
and V
BAT
PF
BAT
PF
. If V
. After V
. However, when V
, the internal clock registers are
PF
CC
CC
is greater than V
level. The device is fully
PF
returns above both V
CC
CC
is less than V
CC
to V
to V
Power Control
Operation
BAT
32kHz TCXO
and once every
CC
BAT
BAT
CC
is applied to
falls below
when V
when V
to detect
BAT
BAT
, the
, the
CC
CC
CC
CC
PF
crosses V
oscillator starts up and the V
oscillator during power-down and keeps the oscillator
running. When the DS3234 switches to V
lator may be disabled by setting the EOSC bit.
There are several modes of operation that affect the
amount of V
powered by V
includes the averaged temperature conversion current,
I
Considerations for Accurate Real-Time Clocks for
details). Temperature conversion current, I
specified since the system must be able to support the
periodic higher current pulse and still maintain a valid
voltage level. Data retention current, I
current drawn by the part when the oscillator is
stopped (EOSC = 1). This mode can be used to mini-
mize battery requirements for times when maintaining
time and date information is not necessary, e.g., while
the end system is waiting to be shipped to a customer.
The DS3234 provides for a pushbutton switch to be
connected to the RST output pin. When the DS3234 is
not in a reset cycle, it continuously monitors the RST
signal for a low going edge. If an edge transition is
detected, the DS3234 debounces the switch by pulling
the RST low. After the internal timer has expired
(PB
If the line is still low, the DS3234 continuously monitors
the line looking for a rising edge. Upon detecting
release, the DS3234 forces the RST pin low and holds it
low for t
The same pin, RST, is used to indicate a power-fail
condition. When V
power-fail signal is generated, which forces the RST pin
low. When V
pin is held low for t
bilize. If the EOSC bit is set to logic 1 (to disable the
oscillator in battery-backup mode), t REC is bypassed
and RST immediately goes high.
Table 1. Power Control
BATTC
V
V
V
V
SUPPLY CONDITION
CC
CC
CC
CC
DB
< V
< V
> V
> V
), the DS3234 continues to monitor the RST line.
, is drawn (refer to Application Note 3644: Power
RST
PF
PF
PF
PF
, V
, V
, V
, V
PF
.
. After the first time V
BAT
CC
CC
CC
CC
CC
BAT
< V
> V
< V
> V
current that is drawn. When the part is
returns to a level above V
BAT
BAT
BAT
BAT
, timekeeping current (I
REC
CC
Pushbutton Reset Function
READ/WRITE
to allow the power supply to sta-
is lower than V
ACCESS
Yes
Yes
Yes
No
V
BAT
BAT
CC
source powers the
SUPPLY
ACTIVE
is ramped up, the
V
V
V
V
Operation
BAT
PF
CC
CC
CC
BATTDR
BAT
BATT
, an internal
PF
, the oscil-
BATTC
, the RST
), which
Inactive
Inactive
, is the
Active
Active
RST
, is