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DS75LXS+-DS75LXU+
Digital Thermometer and Thermostat with Extended Addressing
DS75LX
Digital Thermometer and Thermostat
with Extended Addressing
GENERAL DESCRIPTION This low-voltage (1.7V to 3.7V) digital thermometer
and thermostat provides 9, 10, 11, or 12-bit digital
temperature readings over a -55°C to +125°C range
with ±2°C accuracy over a -25°C to +100°C range. At
power-up, the DS75LX defaults to 9-bit resolution for
software compatibility with the LM75. Communication
with the DS75LX is achieved through a simple 2-wire
serial interface. Three tri-state address pins allow up
to 27 DS75LX devices to operate on the same 2-wire
bus, which greatly simplifies distributed temperature-
sensing applications.
The DS75LX thermostat has a dedicated open-drain
output (O.S.) and programmable fault tolerance,
which allow the user to define the number of
consecutive error conditions that must occur before
O.S. is activated. There are two thermostatic
operating modes that control thermostat operation
based on user-defined trip-points (TOS and THYST).
APPLICATIONS Any Thermally Sensitive System
Cellular Base Stations
Telecom Switches and Routers
Servers
PIN CONFIGURATIONS
FEATURES
1.7V to 3.7V Operating Range
Tri-State Address Pins Allow Up to 27 Unique
Bus Addresses
Temperature Measurements Require No
External Components
Measures Temperatures from -55°C to +125°C
(-67°F to +257°F) ±2°C Accuracy from -25°C to +100°C
Thermometer Resolution Is User-
Configurable from 9 (Default) to 12 Bits (0.5°C
to 0.0625°C Resolution)
9-Bit Conversion Time is 25ms (max)
Thermostatic Settings are User-Definable
Data is Read/Written Through 2-Wire Serial
Interface (SDA and SCL Pins)
Data Lines Filtered Internally for Noise
Immunity (50ns Deglitch)
Bus Timeout Feature Prevents Lockup
Problems on 2-Wire Interface
Multidrop Capability Simplifies Distributed
Temperature-Sensing Applications
Pin/Software Compatible with the LM75
Available in 8-Pin μSOP (μMAX®) and SO
Packages
ORDERING INFORMATION
PART TEMP RANGE PIN
PACKAGE DS75LXS+ -55°C to +125°C 8 SO
(150 mils)
DS75LXS+T&R -55°C to +125°C
8 SO
(150 mils),
2500 Piece
DS75LXU+ -55°C to +125°C 8 μSOP
(μMAX)
DS75LXU+T&R -55°C to +125°C
8 μSOP
(μMAX),
3000 Piece
+ Denotes lead-free package.
T&R denotes tape-and-reel.
Note: A “+” symbol will also be marked on the package near the pin 1 indicator.
μMAX is a registered trademark of Maxim Integrated Products, Inc.
SO (150 mils)
SCL
VDDGND
O.S.
SDA
DS75
LX μSOP/μMAX
SCL
VDDGND
O.S.
SDA
DS75
LX
DS1386/DS1386P
ABSOLUTE MAXIMUM RATINGS Voltage Range on VDD, Relative to Ground -0.3V to +4.0V
Voltage Range on Any Other Pin, Relative to Ground -0.3V to +6.0V
Operating Temperature Range -55°C to +125°C
Storage Temperature Range -55°C to +125°C
Soldering Temperature See IPC/JEDEC J-STD-020
These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operation
sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
The Dallas Semiconductor DS75LX is built to the highest quality standards and manufactured for long-term
reliability. All Dallas Semiconductor devices are made using the same quality materials and manufacturing
methods. However, the DS75LX is not exposed to environmental stresses, such as burn-in, that some industrial
applications require. For specific reliability information on this product, contact the factory in Dallas at (972) 371-
4448.
DC ELECTRICAL CHARACTERISTICS (1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C.)
PARAMETER SYMBOL CONDITIONS MIN MAX UNITS Supply Voltage VDD(Note 1) 1.7 3.7 V
-25°C to +100°C ±2.0 Thermometer Error
(Note 2) TERR-55°C to +125°C ±3.0 °C
Input Logic-High SDA,
SCL VIH(Note 3) 0.7 x VDDVDD + 0.3 V
Input Logic-Low SDA,
SCL VIL VSS - 0.3 0.3 x VDDV
VOL13mA sink current 0 0.4 SDA Output Logic-Low
Voltage (Note 3) VOL26mA sink current 0 0.6 V
O.S. Saturation Voltage VOL4mA sink current
(Notes 2, 3) 0.8 V
Input Current SDA, SCL 0.4 < VI/O < 0.9VDD-10 +10 μA
I/O Capacitance CI/O 10 pF
Address Input Sink
Current ILAHA0, A1, or A2 tied to VDD
(Notes 4, 5) 0.2 3.5 μA
Address Input Source
Current ILALA0, A1, or A2 tied to GND
(Notes 4, 5) 0.2 3.5 μA
Address Voltage High VAH(Note 6) VDD - .04 V
Address Voltage Low VAL(Note 6) VSS + .04 V
Standby Current IDD1(Notes 4, 5) 13 μA
Active temp conversions 1000 Active Current
(Notes 1, 4, 5) IDDCommunication only 100 μA
AC ELECTRICAL CHARACTERISTICS (1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Resolution 9 12 Bits
9-bit conversions 25
10-bit conversions 50
11-bit conversions 100
Temperature Conversion
Time tCONVT
ms
DS75LX: Digital Thermometer and Thermostat with Extended Addressing
SCL Frequency fSCL
AC ELECTRICAL CHARACTERISTICS (continued) (1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C.)
PARAMETER SYMBOL CONDITIONS MIN Bus Free Time Between
a STOP and START
Condition
tBUF(Note 7) 1.3
START and Repeated
START Hold Time from
Falling SCL
tHD:STA(Notes 7, 8) 600
Low Period of SCL tLOW(Note 7) 1.3
High Period of SCL tHIGH(Note 7) 0.6
Repeated START
Condition Setup Time to
Rising SCL
tSU:STA(Note 7) 600
Data-Out Hold Time from
Falling SCL tHD:DAT(Notes 7, 9) 0 0.9 μs
Data-In Setup Time to
Rising SCL tSU:DAT(Note 7) 100 ns
Rise Time of SDA and
SCL (Receive) tR(Notes 7, 10) 20 +
0.1CBB 300 ns
Fall Time of SDA and
SCL (Receive) tF(Notes 7, 10) 20 +
0.1CBB 300 ns
Spike Suppression
Filter Time (Deglitch
Filter)
tSS 0 50 ns
STOP Setup Time to
Rising SCL tSU:STO(Note 7) 600 ns
Capacitive Load for Each
Bus Line CBB 400 pF
Input Capacitance CI 5 pF
Serial Interface Reset
Time tTIMEOUTSDA time low
(Notes 11, 12) 75 325 ms
Note 1: VDD must be decoupled with a high-quality 0.1μF bypass capacitor. X5R or X7R ceramic surface-mount capacitors are
recommended.
Note 2: Internal heating caused by O.S. loading causes the DS75LX to read approximately 0.5°C higher if O.S. is sinking the max
rated current.
Note 3: All voltages are referenced to ground.
Note 4: IDD specified with O.S. pin open and A0–A2 pins grounded.
Note 5: IDD and address leakage specified with VDD at 3.0V and SDA, SCL = 3.0V at 0°C to +70°C.
Note 6: Address pins A0, A1, A2 are directly connected to VDD, VSS, or floating with less than 50pF capacitive load.
Note 7: See the timing diagram (Figure 1). All timing is referenced to 0.9 x VDD and 0.1 x VDD.
Note 8: After this period, the first clock pulse is generated.
Note 9: The DS75LX provides an internal hold time of at least 75ns on the SDA signal to bridge the undefined region of SCL's falling
edge.
Note 10: For example, if CB = 300pF, then tR[min] = tF[min] = 50ns.
Note 11: This timeout applies only when the DS75LX is holding SDA low. Other devices can hold SDA low indefinitely and the DS75LX
will not reset.
Note 12: The DS75LX is available with timeout feature disabled upon special order. Contact Factory.
PIN DESCRIPTION
PIN NAME FUNCTION SDA Data Input/Output for 2-Wire Serial Communication Port (Open Drain) SCL Clock Input for 2-Wire Serial Communication Port O.S. Thermostat Output Open Drain
4 GND Ground
5 A2Address Input
6 A1Address Input
7 A0Address Input
DS75LX: Digital Thermometer and Thermostat with Extended Addressing
BLOCK DIAGRAM TOS AND THYST
REGISTERS
CONFIGURATION
REGISTER
TEMPERATURE
REGISTER
OVERSAMPLING
MODULATOR
PRECISION
REFERENCE
DIGITAL
DECIMATOR
ADDRESS
AND
I/O CONTROL
SCL
Figure 1. Timing Diagram SDA
VDD
GND
THERMOSTAT
COMPARATOR
O.S.
DS75LX: Digital Thermometer and Thermostat with Extended Addressing
OPERATION—MEASURING TEMPERATURE The DS75LX measures temperature using a bandgap temperature-sensing architecture. An on-board delta-sigma
analog-to-digital converter (ADC) converts the measured temperature to a digital value that is calibrated in degrees
celsius; for Fahrenheit applications a lookup table or conversion routine must be used. The DS75LX is factory-
calibrated and requires no external components to measure temperature.
At power-up the DS75LX immediately begins measuring and converting its own temperature to a digital value. The
resolution of the digital output data is user-configurable to 9, 10, 11, or 12 bits, corresponding to temperature
increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C, respectively, with 9-bit default resolution at power-up. The
resolution is controlled via the R0 and R1 bits in the configuration register as explained in the Configuration
Register section of this data sheet. Note that the conversion time doubles for each additional bit of resolution.
After each temperature measurement and analog-to-digital conversion, the DS75LX stores the temperature as a
16-bit two’s complement number in the 2-byte temperature register (see Figure 2). The sign bit (S) indicates if the
temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. The most recently
converted digital measurement can be read from the temperature register at any time. Since temperature
conversions are performed in the background, reading the temperature register does not affect the operation in
progress.
Bits 3 through 0 of the temperature register are hardwired to 0. When the DS75LX is configured for 12-bit
resolution, the 12 MSbs (bits 15 through 4) of the temperature register contain temperature data. For 11-bit
resolution, the 11 MSbs (bits 15 through 5) of the temperature register contain data, and bit 4 reads out as 0.
Likewise, for 10-bit resolution, the 10 MSbs (bits 15 through 6) contain data, and for 9-bit the 9 MSbs (bits 15
through 7) contain data, and all unused LSbs will contain 0s. Table 1 gives examples of 12-bit resolution digital
output data and the corresponding temperatures.
Figure 2. Temperature, TH, and TL Register Format bit 15 bit 14 bit 13 bit 12 bit 11 bit 10 bit 9 bit 8
MS Byte S 26252423222120bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
LS Byte 2-12-22-32-40 0 0 0
Table 1. 12-Bit Resolution Temperature/Data Relationship
TEMPERATURE (°C) DIGITAL OUTPUT
(BINARY)
DIGITAL OUTPUT
(HEX) +125 0111 1101 0000 0000 7D00h
+25.0625 0001 1001 0001 0000 1910h
+10.125 0000 1010 0010 0000 0A20h
+0.5 0000 0000 1000 0000 0080h 0000 0000 0000 0000 0000h
-0.5 1111 1111 1000 0000 FF80h
-10.125 1111 0101 1110 0000 F5E0h
-25.0625 1110 0110 1111 0000 E6F0h
-55 1100 1001 0000 0000 C900h
DS75LX: Digital Thermometer and Thermostat with Extended Addressing
Shutdown Mode
For power-sensitive applications, the DS75LX offers a low-power shutdown mode. The SD bit in the configuration
register controls shutdown mode. When SD is changed to 1, the conversion in progress is completed and the result
is stored in the temperature register after which the DS75LX goes into a low-power standby state. The O.S. output
is cleared if the thermostat is operating in interrupt mode, and O.S remains unchanged in comparator mode. The 2-
wire interface remains operational in shutdown mode, and writing a 0 to the SD bit returns the DS75LX to normal
operation.
OPERATION—THERMOSTAT
The DS75LX thermostat has two operating modes, comparator mode and interrupt mode, which activate and
deactivate the open-drain thermostat output (O.S.) based on user-programmable trip-points (TOS and THYST). The
DS75LX powers up with the thermostat in comparator mode with active-low O.S. polarity and with the
overtemperature trip-point (TOS) register set to +80°C and the hysteresis trip-point (THYST) register set to +75°C. If
these power-up settings are compatible with the application, the DS75LX can be used as a stand-alone thermostat
(i.e., no 2-wire communication required). If interrupt mode operation, active-high O.S. polarity, or different TOS and
THYST values are desired, they must be programmed after power-up, so stand-alone operation is not possible.
In both operating modes, the user can program the thermostat fault tolerance, which sets how many consecutive
temperature readings (1, 2, 4, or 6) must fall outside of the thermostat limits before the thermostat output is
triggered. The fault tolerance is set by the F1 and F0 bits in the configuration register and at power-up the fault
tolerance is 1.
The data format of the TOS and THYST registers is identical to that of the temperature register (see Figure 2), i.e., a
2-byte two’s complement representation of the trip-point temperature in degrees celcius with bits 3 through 0
hardwired to 0. After every temperature conversion, the measured temperature is compared to the values in the
TOS and THYST registers, and then O.S. is updated based on the result of the comparison and the operating mode.
The number of TOS and THYST bits used during the thermostat comparison is equal to the conversion resolution set
by the R1 and R0 bits in the configuration register. For example, if the resolution is 9 bits, only the 9 MSbs of TOS
and THYST will be used by the thermostat comparator.
The active state of the O.S. output can be changed by the POL bit in the configuration register. The power-up
default is active low.
If the user does not wish to use the thermostat capabilities of the DS75LX, the O.S. output should be left floating.
Note that if the thermostat is not used, the TOS and THYST registers can be used for general storage of system data.
Comparator Mode
When the thermostat is in comparator mode, O.S. can be programmed to operate with any amount of hysteresis.
The O.S. output becomes active when the measured temperature exceeds the TOS value a consecutive number of
times as defined by the F1 and F0 fault tolerance (FT) bits in the configuration register. O.S. then stays active until
the first time the temperature falls below the value stored in THYST. Putting the device into shutdown mode does not
clear O.S. in comparator mode. Thermostat comparator mode operation with FT = 2 is illustrated in Figure 3.
Interrupt Mode
In interrupt mode, the O.S. output first becomes active when the measured temperature exceeds the TOS value a
consecutive number of times equal to the FT value in the configuration register. Once activated, O.S. can only be
cleared by either putting the DS75LX into shutdown mode or by reading from any register (temperature,
configuration, TOS, or THYST ) on the device. Once O.S. has been deactivated, it will only be reactivated when the
measured temperature falls below the THYST value a consecutive number of times equal to the FT value. Again, O.S
can only be cleared by putting the device into shutdown mode or reading any register. Thus, this interrupt/clear
process is cyclical between TOS and THYST events (i.e, TOS, clear, THYST, clear, TOS, clear, THYST, clear, etc.).
Thermostat interrupt mode operation with FT = 2 is illustrated in Figure 3.
DS75LX: Digital Thermometer and Thermostat with Extended Addressing
Figure 3. O.S. Output Operation Example
Configuration Register
The configuration register allows the user to program various DS75LX options such as conversion resolution,
thermostat fault tolerance, thermostat polarity, thermostat operating mode, and shutdown mode. The configuration
register is arranged as shown in Figure 4 and detailed descriptions of each bit are provided in Table 2. The user
has read/write access to all bits in the configuration register except the MSb, which is a reserved read-only bit. The
entire register is volatile, and thus powers up in its default state.
Figure 4. Configuration Register
MSb bit 6 bit 5 bit 4bit 3bit 2bit 1LSb
0 R1 R0 F1 F0 POL TM SD
In this example the
DS75LX is configured to
have a fault tolerance of 2.
O.S. Output - Comparator Mode
Conversions
Inactive
Active
Temperature
TOS
THYST
Inactive
Active
O.S. Output - Interrupt Mode
Assumes an interrupt
clear event
has occurred
