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FEATURES

Measures temperatures from -55°C to
+125°C; Fahrenheit equivalent is -67°F to
257°F

Real time clock counts seconds, minutes,
hours, date of the month, month, day of the
week, and year with leap year compensation
through the year 2100

Thermometer accuracy is ą2.0°C (typ)

Thermometer resolution is 9 bits (expandable)

Thermostatic and time alarm settings are user
definable. Dedicated open-drain Alarm output

32 bytes SRAM for general data storage

Data is read from/written to via a 2-wire serial
interface. (open drain I/O lines)

Wide power supply range (2.2V - 5.5V)

Applications include personal
computers/PDAs, cellular telephones, office
equipment, dataloggers, or any thermally
sensitive system

8-pin 150mil SOIC package

PIN ASSIGNMENT

PIN DESCRIPTION

SDA

- 2-Wire Serial Data Input/Output

SCL

- 2-Wire Serial Clock

GND

- Ground

ALRM

- Thermostat & Clock Alarm
Output

- 32.768 kHz Crystal Input

- 32.768 kHz Crystal Feedback
Output

OSC

- Buffered Oscillator Output

- Power Supply Voltage (+2.2V to
+5V)

DESCRIPTION

The DS1629 2-Wire Digital Thermometer and Real Time Clock integrates the critical functions of a real
time clock and a temperature monitor in a small outline 8-pin SOIC package. Communication to the
DS1629 is accomplished via a 2-wire interface. The wide power supply range and minimal power
requirement of the DS1629 allow for accurate time/temperature measurements in battery-powered
applications.

The digital thermometer provides 9-bit temperature readings which indicate the temperature of the device.
No additional components are required; the device is truly a "temperature-to-digital" converter.
The clock/calendar provides seconds, minutes, hours, day, date of the month, day of the week, month, and
year. The end of the month date is automatically adjusted for months with less than 31 days, including
corrections for leap years. It operates in either a 12- or 24-hour format with AM/PM indicator in 12-hour
mode.The crystal oscillator frequency is internally divided, as specified by device configuration. An
open-drain output is provided that can be used as the oscillator input for a microcontroller.

DS1629

2-Wire Digital Thermometer

and Real Time Clock

www.dalsemi.com

1
2
3
4

8
7
6
5

GND

ALRM

SCL

SDA

OSC
X

DS1629S 8-Pin SOIC

(150-mil)

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The open-drain alarm output of the DS1629 will become active when either the measured temperature
exceeds the programmed over-temperature limit (T

) or current time reaches the programmed alarm

setting. The user can configure which event (time only, temperature only, either, or neither) will generate
an alarm condition. For storage of general system data or time/temperature datalogging, the DS1629
features 32 bytes of SRAM. Applications for the DS1629 include personal computers/ PDAs, cellular
telephones, office equipment, thermal dataloggers, or any microprocessor-based, thermally-sensitive
system.

DETAILED PIN DESCRIPTION Table 1

PIN

SYMBOL

DESCRIPTION

SDA

Data input/output pin for 2-wire serial communication port.

SCL

Clock input/output pin for 2-wire serial communication port.

ALRM

Alarm output Open drain time/temperature alarm output with configurable active
state

GND

Ground pin.

32.768 kHz Feedback Output .

32.768 kHz Crystal input.

OSC

Oscillator Output. Open-drain output used for microcontroller clock input.

Supply voltage 2.2V - 5.5V input power pin.

OVERVIEW

A block diagram of the DS1629 is shown in Figure 1.
The DS1629 consists of six major components:

Direct-to-digital temperature sensor

Real time clock

2-wire interface

Data registers

Thermal & clock alarm comparators

Oscillator divider & buffer

The factory-calibrated temperature sensor requires no external components. The very first time the
DS1629 is powered up it begins temperature conversions, and performs conversions continuously. The
host can periodically read the value in the temperature register, which contains the last completed
conversion. As conversions are performed in the background, reading the temperature register does not
affect the conversion in progress.

The host can modify DS1629 configuration such that it does not power up in the auto-convert or
continuous convert modes. This could be beneficial in power-sensitive applications.

The real time clock/calendar maintains a BCD count of seconds, minutes, hours, day of the week, day of
the month, month, and year. It does so with an internal oscillator/ divider and a required 32.768 kHz
crystal. The end of the month date is automatically updated for months with less than 31 days, including
compensation for leap years through the year 2100. The clock format is configurable as a 12- (power-up
default) or 24-hour format, with an AM/PM indicator in the 12-hour mode. The RTC can be shut down
by clearing a bit in the clock register.

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The crystal frequency is internally divided by a factor that the user defines. The divided output is buffered
and can be used to clock a microcontroller.

The DS1629 features an open-drain alarm output. It can be configured to activate on a thermal event, time
event, either thermal or time, or neither thermal nor time (disabled, power-up state). The thermal alarm
becomes active when measured temperature is greater than or equal to the value stored in the TH
thermostat register. It will remain active until temperature is equal to or less than the value stored in TL,
allowing for programmable hysteresis. The clock alarm will activate at the specific minute of the week
that is programmed in the clock alarm register. The time alarm is cleared by reading from or writing to
either the clock register or the clock alarm register.

The DS1629 configuration register defines several key items of device functionality. It sets the
conversion mode of the digital thermometer and what event, if any, will constitute an alarm condition. It
also sets the active state of the alarm output. Finally, it enables/disables and sets the division factor for the
oscillator output.

The DS1629 also features 32 bytes of SRAM for storage of general information. This memory space has
no bearing on thermometer or chronograph operation. Possible uses for this memory are
time/temperature histogram storage, thermal datalogging, etc.

Digital data is written to/read from the DS1629 via a 2-wire interface, and all communication is MSb
first. Individual registers are accessed by unique 8-bit command protocols.

The DS1629 features a wide power supply range (2.2V

5.5V) for clock functionality, SRAM

data retention, and 2-wire communication. EEPROM writes and temperature conversions should only be
performed at 2.7V

5.5V for reliable results.

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DS1629 FUNCTIONAL BLOCK DIAGRAM Figure 1

OPERATION-Measuring Temperature

The DS1629 measures temperature through the use of an on-chip temperature measurement technique
with an operating range from -55

C to +125

C. The device can be configured to perform a single

conversion, store the result, and return to a standby mode or it can be programmed to convert
continuously. Regardless of the mode used, the last completed digital temperature conversion is retrieved
from the temperature register using the Read Temperature (AAh) protocol, as described in detail in the
"Command Set" section. Details on how to change the settings after power-up are contained in the
"OPERATION-Configuration" section.

The DS1629 measures temperature by counting the number of clock cycles that an oscillator with a low
temperature coefficient goes through during a gate period determined by a high temperature coefficient
oscillator. The counter is preset with a base count that corresponds to -55

C. If the counter reaches 0

before the gate period is over, the temperature register, which is also preset to the -55

C value, is

incremented, indicating that the temperature is higher than -55

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At the same time, the counter is then preset with a value determined by the slope accumulator circuitry.
This circuitry is needed to compensate for the parabolic behavior of the oscillators over temperature. The
counter is then clocked again until it reaches 0. If the gate period is still not finished, then this process
repeats.

The slope accumulator is used to compensate for the nonlinear behavior of the oscillators over
temperature, yielding a high resolution temperature measurement. This is done by changing the number
of counts necessary for the counter to go through for each incremental degree in temperature. To obtain
the desired resolution, therefore, both the value of the counter and the number of counts per degree C (the
value of the slope accumulator) at a given temperature must be known.

Internally, this calculation is done inside the DS1629 to provide 0.5

C resolution. Table 2 describes the

exact relationship of output data to measured temperature. For Fahrenheit usage, a lookup table or
conversion factor must be used.

Note that temperature is represented in the DS1629 in terms of a 0.5

C LSB, yielding the 9-bit format

illustrated in Table 2. Higher resolutions may be obtained by implementing the algorithm in Application
Note 105 and performing the following calculation. The 8-bit COUNT_REMAIN value can be obtained
via the Read Counter (A8h) command and the COUNT_PER_C value (also 8-bit) is read via the Read
Slope command (A9h).

T = TEMP_READ -0.25 +

COUNT_PER_

EMAIN)

_C_COUNT_R

(COUNT_PER

Temperature/Data Relationships Table 2

MSB

MSb

(unit = °C)

LSb

-1

LSB

TEMPERATURE

DIGITAL OUTPUT

(Binary)

DIGITAL OUTPUT

(Hex)

+125°C

01111101 00000000

7D00h

+25°C

00011001 00000000

1900

0.5°C

00000000 10000000

0080

0°C

00000000 00000000

0000

-0.5°C

11111111 10000000

FF80

-25°C

11100111 00000000

E700h

-55°C

11001001 00000000

C900h

Part Number DS1629