STLM75_08 STMICROELECTRONICS | Alldatasheet
Document overview
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- PDF pages: 37
Technical content
Datasheet sections
- 1 Description
- 1.1 Serial communications
- 1.2 Temperature sensor output
- 1.3 Pin descriptions
- 1.3.1 SDA (open drain)
- 1.3.2 SCL
- 1.3.4 GND
- 1.3.5 A2, A1, A0
- 2 Operation
- 2.1 Applications information
- 2.2 Thermal alarm function
- 2.3 Comparator mode
- 2.4 Interrupt mode
- 2.5 Fault tolerance
- 2.6 Shutdown mode
- 2.7 Temperature data format
- 2.8 Bus timeout feature
- 3 Functional description
- 3.1 Registers and register set formats
- 3.1.1 Command/pointer register
- 3.1.2 Configuration register
- 3.1.3 Temperature register
- 3.1.4 Over-limit temperature register (T
- 3.1.5 Hysteresis temperature register (T HYS)
- 3.2 Power-up default conditions
- 3.3 Serial interface
- 3.4.1 Bus not busy
- 3.4.2 Start data transfer
Features
■ Measures temperatures from –55°C to +125°C (–67°F to +257°F) – ±2°C accuracy from –25°C to +100°C (max) ■ Low operating current: 125 µA (typ) ■ No external components required ■ 2-wire I2C/SMBus-compatible serial interface – Supports bus time-out feature – Selectable bus address allows connection of up to eight devices on the bus ■ Wide power supply range-operating voltage range: 2.7 V to 5.5 V ■ Conversion time is 150 ms (max) ■ Programmable temperature threshold and hysteresis set points ■ Pin- and software-compatible with LM75 (drop- in replacement) ■ Power-up defaults permit standalone operation as a thermostat ■ Shutdown mode to minimize power consumption ■ Output pin (open drain) can be configured for interrupt or comparator/thermostat mode (dual purpose event pin) ■ Packages: –S O 8 – MSOP8 (TSSOP8) SO8 (M) MSOP8 (TSSOP8) (DS)
Table 8. T
1 Description
The STLM75 is a high-precision digital CMOS temperature sensor IC with a sigma-delta temperature-to-digital converter and an I2C-compatible serial digital interface (see Figure 1 on page 7). It is targeted for general applications such as personal computers, system thermal management, electronics equipment, and industrial controllers, and is packaged in the industry standard 8-lead TSSOP and SO8 packages. The device contains a band gap temperature sensor and 9-bit ADC which monitor and digitize the temperature to a resolution up to 0.5°C. The STLM75 is typically accurate to (±3°C - max) over the full temperature measurement range of –55°C to 125°C with ±2°C accuracy in the –25°C to +100°C range. The STLM75 is pin-for-pin and software compatible with the LM75B. STLM75 is specified for operating at supply voltages from 2.7 V to 5.5 V. Operating at 3.3 V, the supply current is typically (125 µA). The on-board sigma-delta analog-to-digital converter (ADC) converts the measured temperature to a digital value that is calibrated in degrees centigrade; for Fahrenheit applications a lookup table or conversion routine is required. The STLM75 is factory-calibrated and requires no external components to measure temperature.
1.1 Serial communications
The STLM75 has a simple 2-wire I2C-compatible digital serial interface which allows the user to access the data in the temperature register at any time. It communicates via the serial interface with a master controller which operates at speeds up to 400 kHz. Three pins (A0, A1, and A2) are available for address selection, and enable the user to connect up to 8 devices on the same bus without address conflict. In addition, the serial interface gives the user easy access to all STLM75 registers to customize operation of the device.
1.2 Temperature sensor output
- Comparator mode, and
- Interrupt mode. At power-up the STLM75 immediately begins measuring the temperature and converting the temperature to a digital value. The measured temperature value is compared with a temperature limit (which is stored in the 16-bit (TOS) READ/WRITE register), and the hysteresis temperature (which is stored in the 16-bit (THYS) READ/WRITE register). If the measured value exceeds these limits, the OS/INT pin is activated (see Figure 3 on page 8 and Table 2 on page 14). Note: See Pin descriptions on page 9 for details.
Figure 1. Logic diagram
- SDA and OS /INT are open drain.
Figure 2. Connections (SO8 and TSSOP8)
- SDA and OS /INT are open drain.
Figure 3. Functional block diagram Table 1. Signal names
- SDA and OS /INT are open drain.
2 SCL Input Serial clock input
4 GND Supply ground Ground
1.3 Pin descriptions
See Figure 1 on page 7 and Table 1 on page 8 for a brief overview of the signals connected to this device.
1.3.1 SDA (open drain)
This is the serial data input/output pin for the 2-wire serial communication port.
1.3.2 SCL
This is the serial clock input pin for the 2-wire serial communication port.
1.3.3 OS /INT (open drain)
This is the over-limit signal/interrupt alert output pin. It is open drain, so it needs a pull-up resistor. In Interrupt mode, it outputs a pulse whenever the measured temperature exceeds the programmed threshold (T OS). It behaves as a thermostat, toggling to indicate whether the measured temperature is above or below the threshold and hysteresis (THYS).
1.3.4 GND
Ground; it is the reference for the power supply. It must be connected to system ground.
1.3.5 A2, A1, A0
A2, A1, and A0 are selectable address pins for the 3 LSBs of the I2C interface address. They can be set to VDD or GND to provide 8 unique address selections.
1.3.6 V DD
This is the supply voltage pin, and ranges from +2.7 V to +5.5 V.
2 Operation
After each temperature measurement and analog-to-digital conversion, the STLM75 stores the temperature as a 16-bit two’s complement number (see Table 5: Register pointers selection summary on page 17) in the 2-byte temperature register (see Table 7 on page 18). The most significant 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. The temperature data is provided by the 9 MSBs (bits 15 through 7). Bits 6 through 0 are unused. Table 3 on page 15 gives examples of the digital output data and corresponding temperatures. The data is compared to the values in the T OS and THYS registers, and then the OS is updated based on the result of the comparison and the operating mode. The alarm fault tolerance is controlled by the FT1 and FT0 bits in the configuration register. They are used to set up a fault queue. This prevents false tripping of the OS/INT pin when the STLM75 is used in a noisy environment (see Table 3 on page 15). The active state of the OS output can be changed via the polarity bit (POL) in the configuration register. The power-up default is active-low. If the user does not wish to use the thermostat capabilities of the STLM75, the OS output should be left floating. Note: If the thermostat is not used, the T OS and THYS registers can be used for general storage of system data.
2.1 Applications information
connection for this type of digital sensor is shown in Figure 4 on page 11.
- System thermal management
- Computers/disk drivers
- Electronics/test equipment
- Power supply modules
- Consumer products
- Battery management
- Fax/printers management
- Automotive
Figure 4. Typical 2-wire interface connections diagram
- SDA and OS /INT are open drain.
2.2 Thermal alarm function
The STLM75 thermal alarm function provides user-programmable thermostat capability and allows the STLM75 to function as a standalone thermostat without using the serial interface. The OS output is the alarm output. This signal is an open drain output, and at power-up, this pin is configured with active-low polarity by default.
2.3 Comparator mode
In comparator mode, each time a temperature-to-digital (T -to-D) conversion occurs, the new digital temperature is compared to the value stored in the T OS and THYS registers. If a fault tolerance number of consecutive temperature measurements are greater than the value stored in the T OS register, the OS output will be asserted. For example, if the FT1 and FT0 bits are equal to “10” (fault tolerance = 4), four consecutive temperature measurements must exceed TOS to activate the OS output. Once the OS output is active, it will remain active until the first time the measured temperature drops below the temperature stored in the THYS register. When the thermostat is in comparator mode, the OS can be programmed to operate with any amount of hysteresis. The OS output becomes active when the measured temperature exceeds the TOS value a consecutive number of times as defined by the FT1 and FT0 fault tolerance (FT) bits in the configuration register. The OS then stays active when the temperature falls below the value stored in THYS register for a consecutive number of times as defined by the fault tolerance bits (FT1 and FT0). Putting the device into shutdown mode does not clear OS in comparator mode.
2.4 Interrupt mode
equal to the FT value. Figure 5 illustrates typical OS output temperature response. the OS/INT pin occur only when the STLM75 is read or placed into shutdown mode. Otherwise, OS/INT would remain active independently for any event. Figure 5. OS output temperature response diagram
- These interrupt mode resets of O.S. occur only when STLM75 is read or placed in shutdown. Otherwise,
O.S. would remain active indefinitely for any event..
2.5 Fault tolerance
these bits both default to logic '0'.
2.6 Shutdown mode
mode, and writing a '0' to the SD bit returns the STLM75 to normal operation. Table 2. Fault tolerance setting
2.7 Temperature data format
Table 3 shows the relationship between the output digital data and the external temperature.
2.8 Bus timeout feature
wait for another START condition. Table 3. Relationship between temperature and digital output
3 Functional description
must “point” to the device register to be accessed.
- Command register/address pointer register
- Configuration register
- Temperature register
- Over-limit signal temperature register (TOS)
- Hysteresis temperature register (THYS)
3.1 Registers and register set formats
3.1.1 Command/pointer register
must be kept '0', see Table 4). The command register retains pointer information between operations (see Table 5). from the same register. All bits in the command register default to '0' at power-up. Table 4. Command/pointer register format
000000 P 1 P 0
3.1.2 Configuration register
mode, OS operation mode, OS polarity, and OS fault queue. thus powers-up in its default state only. Table 5. Register pointers selection summary
16 R/W 5000
Table 6. Configuration register format
- Indicates operation mode; 0 = comparator mode, and 1 = interrupt mode (see Comparator mode and
- The OS is active-low ('0').
FT0 = fault tolerance0 bit Bit 7 = must be set to '0'. Reserved.
3.1.3 Temperature register
the T -to-D conversion is finished. Note: These are comparable formats to the LM75.
3.1.4 Over-limit temperature register (T OS)
register, and all remaining bits are “Don’t cares”. Table 7. Temperature register format
3.1.5 Hysteresis temperature register (T HYS)
format (see Table 8). This register defaults to 75°C at power-up (i.e., 0100 1011 0000 0000). contains the sign bit for the digital temperature and Bit14 contains the temperature MSB. Note: These are comparable formats to the DS75 and LM75.
3.2 Power-up default conditions
- Thermostat mode = comparator mode
- Polarity = active-low
- Fault tolerance = 1 fault (i.e., relevant bits set to '0' in the configuration register)
- TOS = 80°C
- THYS = 75°C
- Register pointer = 00 (temperature register) Note: After power-up these conditions can be reprogrammed via the serial interface.
Table 8. T OS and THYS register format
3.3 Serial interface
generates the SCL signal which provides the clock signal for all other devices on the bus. (see Table 9). Both the master and slave devices can send and receive data on the bus. followed by an acknowledge (ACK) or not acknowledge (NACK) from the receiving device. connected to a positive supply voltage via a pull-up resistor.
- Data transfer may be initiated only when the bus is not busy.
- During data transfer, the data line must remain stable whenever the clock line is high.
- Changes in the data line, while the clock line is high, will be interpreted as control signals. Accordingly, the following bus conditions have been defined (see Figure 6 on page 21):
3.4.1 Bus not busy
Both data and clock lines remain high.
3.4.2 Start data transfer
3.4.3 Stop data transfer
Table 9. STLM75 serial bus slave addresses
3.4.4 Data valid
changed during the low period of the clock signal. There is one clock pulse per bit of data. Each data transfer is initiated with a start condition and terminated with a stop condition. The number of data bytes transferred between the start and stop conditions is not limited. The information is transmitted byte-wide and each receiver acknowledges with a ninth bit. “master”. The devices that are controlled by the master are called “slaves”. Figure 6. Serial bus data transfer sequence
3.4.5 Acknowledge
Figure 7. Acknowledgement sequence
3.5 READ mode
address 'An' is written to the on-chip address pointer.
- Preset pointer locations (e.g. temperature, TOS and THYS registers), and
- Pointer setting (the pointer has to be set for the register that is to be read) Note: The temperature register pointer is usually the default pointer. These modes are shown in the READ mode typical timing diagrams (see Figure 9, Figure 10, and Figure 11).
Figure 8. Slave address location
3.6 WRITE mode
is to be written to the on-chip address pointer. Figure 12. Typical pointer set followed by an immediate READ from the Figure 13. Configuration register WRITE
001 A 2 A 1 A 0 R / W 000000 000 D 4 D 3 D 2 D 1 D 0 D1 D0
Figure 14. T OS and THYS WRITE
4 Typical operating characteristics
Figure 15. Temperature variation vs. voltage
5 Maximum ratings
Program and other relevant quality documents. Table 10. Absolute maximum ratings
- Reflow at peak temperature of 255°C to 260°C for < 30 seconds (total thermal budget not to exceed 180°C
for between 90 to 150 seconds).
6 DC and AC parameters
Table 11. Operating and AC measurement conditions
Table 12. DC and AC characteristics
- Valid for ambient operating temperature: T A = –55 to 125°C; VDD = 2.7 V to 5.5 V (except where noted).
- Typical number taken at V DD = 3 V, TA = 25°C
2.7 V ≤ V
Figure 16. Bus timing requirements sequence Table 13. AC characteristics
- Valid for ambient operating temperature: T A = –55 to 125°C; VDD = 2.7 V to 5.5 V (except where noted).
- T ransmitter must internally provide a hold time to bridge the undefined region (300 ns max) of the falling
- For SMBus compatibility, the STLM75 supports bus ti me-out. Holding the SDA line low for a time greater
7 Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK® packages. These packages have a Lead-free second level interconnect. The category of second Level Interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com.
Figure 17. SO8 – 8-lead plastic small package outline Note: Drawing is not to scale. Table 14. SO8 – 8-lead plastic small outline package mechanical data
Figure 18. MSOP8 (TSSOP8) – 8-lead, thin shrink small package (3x3) outline Note: Drawing is not to scale. Table 15. MSOP8 (TSSOP8) – 8-lead, thin shrink small package (3x3) mechanical
8 Part numbering
Table 16. Ordering information scheme ST sales office nearest you.
9 Revision history
Table 17. Document revision history 23-Dec-2005 1 Initial release. Figure 18, Table 15) and part numbering (Table 16). and part numbering (Table 16). Section 3.1.3: Temperature register. 18-Jul-2008 9 Updated cover page and Table 16.