DS75S Fast Delivery |IC PHOENIX CO.,LIMITED

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DS75S
2.Wire Thermal Watchdog
FEATURES
=Temperature measurements require no
external componentsMeasures temperatures from –55°C to
+125°C. Fahrenheit equivalent is –67°F to
+257°F.Thermometer accuracy is ±2.0°C.Thermometer resolution is configurable from
nine (default) to 12 bits (0.5°C to 0.0625°C
resolution)9–bit readout mode features a maxconversion time of 150 ms.Thermostatic settings are user definable.Data is read from/written via a 2–wire serial
interface. (open drain I/O lines). 3–bit
addressabilityWide power supply range (2.7V – 5.5V).Applications include personal computers,
cellular telephones, office equipment, or any
thermally sensitive system.Pin/software compatible to LM75CIM–xThermal Watchdog in 9–bit (default) mode.8–pin 150 mil SOIC package.
PIN ASSIGNMENT
PIN DESCRIPTION
SDA – 2–Wire Serial Data Input/OutputSCL – 2–Wire Serial Clock
GND – Ground
O.S. – Thermostat Output Signal
A0 – Chip Address Input
A1 – Chip Address InputA2 – Chip Address Input
V DD – Power Supply Voltage
DESCRIPTION
The DS75 2–wire thermal watchdog provides 9–bit temperature readings which indicate the temperatureof the device. Thermostat settings and temperature readings are all communicated to/from the DS75 over
a simple 2–wire serial interface. No additional components are required; the device is truly a
“temperature–to–digital” converter.
The DS75 has three address bits that allow a user to multidrop up to eight sensors along the 2–wire bus,
greatly simplifying the bussing of distributed temperature sensing networks.
The open–drain thermal alarm output, O.S., becomes active when the temperature of the device exceeds a
user–defined temperature TOS. The number of consecutive faults required to set O.S. active is
configurable by the user. The device can also be configured in the interrupt or comparator mode, to
customize the method which clears the fault condition.
For applications that require greater temperature resolution, the user can adjust the readout resolution
from 9 to 12 bits. This is particularly useful in applications where thermal runaway conditions must be
DS75
2–Wire Thermal Watchdog
O.S.
GND
VDD
SCL
DS75
Applications for the DS75 include personal computers/servers, cellular telephones, office equipment, or
any microprocessor–based thermally–sensitive system.
DETAILED PIN DESCRIPTION Table 1
OVERVIEW
A block diagram of the DS75 is shown in Figure 1. The DS75 consists of five major components:
1. Precision temperature sensor2. Analog–to–digital converter
3. 2–wire interface electronics
4. Data registers
5. Thermostat comparator
The factory–calibrated temperature sensor requires no external components. Upon power–up, the DS75
begins temperature conversions with the default resolution of 9 bits (0.5°C resolution). The host can
periodically read the value in the temperature register, which contains the last completed conversion. Asconversions are performed in the background, reading the temperature register does not affect the
conversion in progress.
In power–sensitive applications, the user can put the DS75 into a shutdown mode, under which the sensorwill complete and store the conversion in progress and revert to a low–power standby state. In
applications where small incremental temperature changes are critical, the user can change the conversion
resolution from 9–bits to 10, 11, or 12. Each additional bit of resolution approximately doubles the
conversion time. This is accomplished by programming the configuration register. The configuration
register defines the conversion state, thermometer resolution/conversion time, active state of thethermostat output, number of consecutive faults to trigger an alarm condition, and the method to
terminate an alarm condition.
The user can also program over–temperature (TOS) and under–temperature (THYST) setpoints for
thermostatic operation. The power–up state of TOS is 80°C and that for THYST is 75°C. The result of each
temperature conversion is compared with the TOS and THYST setpoints. The DS75 offers two modes for
temperature control, the comparator mode and the interrupt mode. This allows the user the flexibility to
customize the condition that would generate and clear a fault condition. Regardless of the mode chosen,
the O.S. output will become active only after the measured temperature exceeds the respective trippoint aconsecutive number of times; the number of consecutive conversions beyond the limit to generate an O.S.
is programmable. The power–up state of the DS75 is in the comparator mode with a single fault
generating an active O.S. Digital data is written to/read from the DS75 via a 2–wire interface, and all
DS75
DS75 FUNCTIONAL BLOCK DIAGRAM Figure 1
OPERATION–Measuring Temperature
The core of DS75 functionality is its direct–to–digital temperature sensor. The DS75 measures
temperature through the use of an on–chip temperature measurement technique with an operating range
from –55°C to +125°C. Temperature conversions are initiated upon power–up, and the most recent resultis stored in the thermometer register. Conversions are performed continuously unless the user intervenes
by altering the configuration register to put the DS75 into a shutdown mode. Regardless of the mode
used, the digital temperature can be retrieved from the temperature register by setting the pointer to that
location (00h, power–up default). The DS75 power–up default has the sensor automatically performing
9–bit conversions continuously. Details on how to change the settings after pow-er up are contained in the“OPERATION– Programming” section.
The resolution of the temperature conversion is configurable (9, 10, 11, or 12 bits), with 9–bit readings
the default state. This equates to a temperature resolution of 0.5°C, 0.25°C, 0.125°C, or 0.0625°C.
Following each conversion, thermal data is stored in the thermometer register in two’s complement
format; the information can be retrieved over the 2–wire interface with the device pointer set to the
temperature register. Table 2 describes the exact relationship of output data to measured temperature. The
table assumes the DS75 is configured for 12–bit resolution; if the device is configured in a lowerresolution mode, those bits will contain zeros. The data is transmitted serially over the 2–wire serial
interface, MSb first. The MSb of the temperature register contains the “sign” (S) bit, denoting whether the
DS75
Temperature/Data Relationships Table 2MSB
MSb(UNIT = °C)LSbLSB
TEMPERATURE/DATA RELATIONSHIPS
Table 2 cont’d
OPERATION–Thermostat Control
In its comparator operating mode, the DS75 functions as a thermostat with programmable hysteresis, as
shown in Figure 2. When the DS75’s temperature meets or exceeds the value stored in the high tempera-ture trip register (TOS ) a consecutive number of times defined by the configuration register, the output
becomes active, and will stay active until the temperature falls below the temperature stored in the low
temperature trigger register (THYST ) the first time. In this way, any amount of hysteresis may be obtained.
The DS75 powers up in the comparator mode with TOS =80°C and THYST =75°C, and the device can beused as a standalone thermostat (no 2–wire interface required) with those setpoints.
In the interrupt mode, the O.S. output will first become active following the programmed number of
consecutive conversions above TOS . The fault can only be cleared by either setting the DS75 in a
shutdown mode or by reading any register (temperature, configuration, TOS, or THYST ) on the device.Following a clear, a subsequent fault can only occur if consecutive conversions fall below THYST. This
interrupt/clear process is thus cyclical (TOS, clear, THYST, clear, TOS, clear, THYST, clear, . . .). Only the
first of multiple consecutive TOS violations will activate O.S., even if each fault is separated by a clearing
function. The same situation applies to multiple consecutive THYST events.
DS75
O.S. OUTPUT TRANSFER FUNCTION Figure 2
Regardless of the mode chosen, the O.S. output is open–drain and the active state is set in the configura-
tion register. The power–up default is active low. Refer to the “OPERATION–Programming” section for
instructions in adjusting the thermostat setpoints, thermostat mode, and O.S. active state.
OPERATION–Programming
There are three areas of interest in programming the DS75: Configuration register, TOS register, and the
THYST register. All programming is done via the 2–wire interface by setting the pointer to the appropriate
location. Table 3 illustrates the pointer settings for the four registers of the DS75.
Pointer Register Structure Table 3
The DS75 will power up with the temperature register selected. If the host wishes to change the data
pointer, it simply addresses the DS75 in the write mode (R/W=0), receives an acknowledge, and writes
the 8 bits that correspond to the new desired location. The last pointer location is always maintained so
that consecutive reads from the same register do not require the host to always provide a pointer address.The only exception is at power–up, in which case the pointer will always be set to 00h, the temperature
register. The pointer address must always proceed data in writing to a register, regardless of which
DS75
Configuration Register Programming
The configuration register is accessed if the DS75 pointer is currently set to the 01h location. Writing to
or reading from the register is determined by the R/W bit of the 2–wire control byte (See “2–wire Serial
Data Bus” section). Data is read from or written to the configuration register MSb first. The format of the
register is illustrated below in Figure 3. The effect each bit has on DS75 functionality is described below
along with the power–up state of the bit. The user has read/write access to all bits in the configurationregister. The entire register is volatile, and thus it will power–up in the default state.
CONFIGURATION/STATUS REGISTER
Figure 3
MSbLSb
SD = Shutdown bit. If SD is “0”, the DS75 will continuously perform temperature conversions and store
the last completed result in the thermometer register. If SD is changed to “1”, the conversion in progress
will be completed and stored; then the device will revert to a low–power standby mode. The O.S. output
will be cleared if the device is in the interrupt mode and remain unchanged in the comparator mode. The2–wire port remains active. The power–up default state is “0” (continuous conversion mode).
TM = Thermostat mode. If TM=“0”, the DS75 is in the comparator mode. TM=“1” sets the device to the
interrupt mode. See “OPERATION–Thermostat Control” section for a description of the difference
between the two modes. The power–up default state of the TM bit is “0” (comparator mode).
POL = O.S. Polarity Bit. If POL =“1”, the active state of the O.S. output will be high. A “0” stored in
this location sets the thermostat output to an active low state. The user has read/write access to the POL
bit, and the power–up default state is “0” (active low).
F0, F1 = O.S. Fault Tolerance bits. The fault tolerance defines the number of consecutive conversionsreturning a temperature beyond limits is required to set the O.S. output in an active state. This may be
necessary to add margin in noisy environments. Table 4 below defines the four settings. The DS75 will
power up with F0=F1=“0”, such that a single occurrence will trigger a fault.
Fault Tolerance Configuration Table 4
R0, R1 = Thermometer resolution bits. Table 5 below defines the resolution of the digital thermometer,
based on the settings of these two bits. There is a direct trade-off between resolution and conversion time,
as depicted in the AC Electrical Characteristics. The default state is R0=0 and R1=0 (9–bit conversions).
“0” = Reserved Location. The master can write to this bit, but it will always read out as a “0”. Thepower–on default state is “0”.
DS75
Thermometer Resolution Configuration
Table 5
Thermostat Setpoints Programming
The thermostat registers (TOS and THYST ) can be programmed or read via the 2–wire interface. TOS is
accessed by setting the DS75 data pointer to the 03h location, and that for the THYST setting is 02h.
The format of the TOS and THYST registers is identical to that of the Thermometer register; that is, 12–bit
2’s complement representation of the temperature in °C. The user can program the number of bits (9, 10,
11, or 12) for each TOS and THYST that correspond to the thermometer resolution mode chosen. If the 9–bitmode is chosen, for example, the 3 least significant bits of TOS and THYST will be ignored by the
thermostat comparator. The format for both TOS and THYST is shown below in Table 6. The power–up
default of TOS is 80°C and that for THYST is 75°C.
Thermostat Setpoint (TOS/THYST) Format
Table 6MSB
MSb(UNIT = °C)LSbLSB
TEMPERATURE/DATA RELATIONSHIPS
If the user does not wish to take advantage of the thermostat capabilities of the DS75, the 24 bits can be
used for general storage of system data that need not be maintained following a power loss. The O.S.

Partno	Mfg	Dc	Qty	Available	Descript
DS75S	MAXIM	N/a	226	avai	2.Wire Thermal Watchdog