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LM75AD-LM75ADP
LM75A; Digital temperature sensor and thermal Watchdog(tm)
Product data sheet
Supersedes data of 2001 Jul 16
2004 Oct 05
Philips Semiconductors Product data sheet
LM75ADigital temperature sensor and thermal Watchdog
GENERAL DESCRIPTIONThe LM75A is a temperature-to-digital converter using an on-chip
band-gap temperature sensor and Sigma-delta A-to-D conversion
technique. The device is also a thermal detector providing an
over-temp detection output. The LM75A contains a number of data
registers: Configuration register (Conf) to store the device settings
such as device operation mode, OS operation mode, OS polarity
and OS fault queue as described in the functional description
section; temperature register (Temp) to store the digital temp
reading, and set-point registers (Tos & Thyst) to store programmable
overtemp shutdown and hysteresis limits, that can be communicated
by a controller via the 2-wire serial I2C-bus interface. The device
also includes an open-drain output (OS) which becomes active
when the temperature exceeds the programmed limits. There are
three selectable logic address pins so that eight devices can be
connected on the same bus without address conflict.
The LM75A can be configured for different operation conditions. It
can be set in normal mode to periodically monitor the ambient
temperature, or in shutdown mode to minimize power consumption.
The OS output operates in either of two selectable modes: OS
comparator mode and OS interrupt mode. Its active state can be
selected as either HIGH or LOW. The fault queue that defines the
number of consecutive faults in order to activate the OS output is
programmable as well as the set-point limits.
The temperature register always stores an 11-bit 2’s complement
data giving a temperature resolution of 0.125 °C. This high
temperature resolution is particularly useful in applications of
measuring precisely the thermal drift or runaway.
The device is powered-up in normal operation mode with the OS in
comparator mode, temperature threshold of 80 °C and hysteresis of
75 °C, so that it can be used as a stand-alone thermostat with those
pre-defined temperature set points.
FEATURES Pin-for-pin replacement for industry standard LM75 and offers
improved temperature resolution of 0.125 °C and specification of
a single part over power supply range from 2.8 V to 5.5 V. Small 8-pin package types: SO8 and TSSOP8I2 C-bus interface with up to 8 devices on the same bus Power supply range from 2.8 V to 5.5 V Temperatures range from –55 °C to +125 °C 11-bit ADC that offers a temperature resolution of 0.125 °C Temperature accuracy of:
±2 °C from –25 °C to +100 °C
±3 °C from –55 °C to +125 °C Programmable temperature threshold and hysteresis set points Supply current of 3.5 μA in shut-down mode for power
conservation Stand-alone operation as thermostat at power-up. ESD protection exceeds 2000 V HBM per JESD22-A114,
200 V MM per JESD22-A115 and 1000 V CDM per JESD22-C101• Latch-up testing is done to JESDEC Standard JESD78 which
exceeds 100 mA
APPLICATIONS System thermal management Personal computers Electronics equipment Industrial controllers.
ORDERING INFORMATIONTamb = –55 °C to +125 °C
Philips Semiconductors Product data sheet
LM75ADigital temperature sensor and thermal Watchdog
PINNING
Pin configuration
Figure 1. SO8 and TSSOP8 pin configurations.
Pin description
SIMPLIFIED BLOCK DIAGRAM
Figure 2. Simplified block diagram.
Philips Semiconductors Product data sheet
LM75ADigital temperature sensor and thermal Watchdog
TYPICAL APPLICATION
Figure 3. Typical application.
ABSOLUTE MAXIMUM RATINGS1
NOTE: This is a stress rating only. Functional operation of the device as indicated in the operational section is not applied to this absolute maximum
rating. Stresses above those listed in ‘Absolute Maximum Ratings’ may cause permanent damage to the device and exposure to any of
these rating conditions for extended periods may affect device reliability.
OPERATING RATINGS
Philips Semiconductors Product data sheet
LM75ADigital temperature sensor and thermal Watchdog
DC ELECTRICAL CHARACTERISTICSVCC = 2.8 V to 5.5 V, Tamb = –55 °C to +125 °C unless otherwise noted.
NOTE: Typical values are at VCC = 3.3 V and Tamb = 25 °C. Conv: device A-to-D conversion.
Philips Semiconductors Product data sheet
LM75ADigital temperature sensor and thermal Watchdog
2 C INTERFACE AC CHARACTERISTICS1VCC = 2.8 V to 5.5 V, Tamb = –55 °C to +125 °C unless otherwise noted.
NOTE: These specifications are guaranteed by design and not tested in production.
Figure 4. Timing diagram.
Philips Semiconductors Product data sheet
LM75ADigital temperature sensor and thermal Watchdog
FUNCTIONAL DESCRIPTION
General operationThe LM75A uses the on-chip band-gap sensor to measure the
device temperature with the resolution of 0.125 °C and stores the
11-bit 2’s complement digital data, resulted from 11-bit A-to-D
conversion, into the device Temp register. This Temp register can be
read at any time by a controller on the I2 C-bus. Reading
temperature data does not affect the conversion in progress during
the read operation.
The device can be set to operate in either mode: normal or
shut-down. In normal operation mode, the temp-to-digital conversion
is executed every 100 ms and the Temp register is updated at the
end of each conversion. In shut-down mode, the device becomes
idle, data conversion is disabled and the Temp register holds the
latest result; however, the device I2 C interface is still active and
register write/ read operation can be performed. The device
operation mode is controllable by programming bit B0 of the
configuration register. The temperature conversion is initiated when
the device is powered-up or put back into normal mode from
shut-down.
In addition, at the end of each conversion in normal mode, the
temperature data (or Temp) in the Temp register is automatically
compared with the over-temp shut-down threshold data (or Tos)
stored in the Tos register, and the hysteresis data (or Thyst) stored
in the Thyst register, in order to set the state of the device OS output
accordingly. The device Tos and Thyst registers are write/read
capable, and both operate with 9-bit 2’s complement digital data.
To match with this 9-bit operation, the temp register uses only the
9 MSB bits of its 11-bit data for the comparison.
The way that the OS output responds to the comparison operation
depends upon the OS operation mode selected by configuration
bit B1, and the user-defined fault queue defined by configuration
bits B3 and B4.
In OS comparator mode, the OS output behaves like a thermostat. It
becomes active when the Temp exceeds the Tos, and is reset when
the Temp drops below the Thyst. Reading the device registers or
putting the device into shut-down does not change the state of the
OS output. The OS output in this case can be used to control
cooling fans or thermal switches.
In OS interrupt mode, the OS output is used for thermal interruption.
When the device is powered-up, the OS output is first activated only
when the Temp exceeds the Tos; then it remains active indefinitely
until being reset by a read of any register. Once the OS output has
been activated by crossing Tos and then reset, it can be activated
again only when the Temp drops below the Thyst; then again, it
remains active indefinitely until being reset by a read of any register.
The OS interrupt operation would be continued in this sequence:
Tos trip, Reset, Thyst trip, Reset, Tos trip, Reset, Thyst trip, Reset, …
Putting the device into shut-down mode also resets the OS output.
In both cases, comparator mode and interrupt mode, the OS output
is activated only if a number of consecutive faults, defined by the
device fault queue, has been met. The fault queue is programmable
and stored in the two bits, B3 and B4, of the Configuration register.
Also, the OS output active state is selectable as HIGH or LOW by
setting accordingly the configuration register bit B2.
At power-up, the device is put into normal operation mode, the Tos
is set to 80 °C, the Thyst is set to 75 °C, the OS active state is
selected LOW and the fault queue is equal to 1. The temp reading
data is not available until the first conversion is completed in about
100 ms.
The OS response to the temperature is illustrated in Figure 5.
Philips Semiconductors Product data sheet
LM75ADigital temperature sensor and thermal Watchdog
2 C serial interfaceThe LM75A can be connected to a compatible 2-wire serial interface2 C-bus as a slave device under the control of a controller or master
device, using two device terminals, SCL and SDA. The controller
must provide the SCL clock signal and write/read data to/from the
device through the SDA terminal. Notice that if the I2C common
pull-up resistors have not been installed as required for I2C-bus,
then an external pull-up resistor, about 10 kΩ, is needed for each of
these two terminals. The bus communication protocols are
described in the data communication section.
Slave addressThe LM75A slave address on the I2C-bus is partially defined by the
logic applied to the device address pins A2, A1 and A0. Each of
them is typically connected either to GND for logic 0, or to VCC for
logic 1. These pins represent the three LSB bits of the device 7-bit
address. The other four MSB bits of the address data are preset to
‘1001’ by hard wiring inside the LM75A. Table 1 shows the device’s
complete address and indicates that up to 8 devices can be
connected to the same bus without address conflict. Because the
input pins, SCL, SDA, A2–A0, are not internally biased, it is
important that they should not be left floating in any application.
Table 1. Address table1 = HIGH, 0 = LOW
Register listThe LM75A contains four data registers beside the pointer register
as listed in Table 2. The pointer value, read/write capability and
default content at power up of the registers are also shown in the
Register table.
Table 2. Register table
Pointer registerThe pointer register contains an 8-bit data byte of which the two
LSB bits represent the pointer value of the other four registers, and
the other 6 MSB bits are equal to 0, as shown in the Pointer register
table (Table 3) and the Pointer value table (Table 4). The pointer
register is not accessible to the user, but is used to select the data
register for write/read operation by including the pointer data byte in
the bus command.
Table 3. Pointer register table
Table 4. Pointer valueBecause the Pointer value is latched into the Pointer register when
the bus command, which includes the pointer byte, is executed, a
read from the LM75A may or may not include the pointer byte in the
statement. To read again a register, which has been recently read
and the pointer has been preset, the pointer byte does not have to
be included. To read a register, which is different with the one that
has been recently read, the pointer byte must be included. However,
a write to the LM75A must always include the pointer byte in the
statement. The bus communication protocols are described in detail
in the data communication section.
At power-up, the Pointer value is equal to 0 and the Temp register is
selected; users can then read the Temp data without specifying the
pointer byte.
Philips Semiconductors Product data sheet
LM75ADigital temperature sensor and thermal Watchdog
Configuration registerThe Configuration register is a write/read register and contains an 8-bit non-complement data byte that is used to configure the device for
different operation conditions. The Configuration register table (Table 5) shows the bit assignments of this register.
Table 5. Configuration register table
Temperature register (Temp)The Temp register holds the digital result of temperature measurement or monitor at the end each A-to-D conversion. This register is read only
and contains two 8-bit data bytes consisting of one most significant (MS) data byte and one least significant (LS) data byte. However, only 11
bits of those two bytes are used to store the Temp data in 2’s complement format with the resolution of 0.125 °C. The Temp register table
(Table 6) shows the bit arrangement of the Temp data in the data bytes.
Table 6. Temp register tableNotice that when the Temp register is read, all 16 bits are provided to the bus and must be all collected by the controller to complete the bus
operation. However, only the 11 significant bits should be used, and the 5 LSB bits of the LS byte are zero and should be ignored. One of the
ways to calculate the Temp value in °C from the 11-bit Temp data is: If the Temp data MSB bit D10 = 0 then the temperature is positive and Temp value (°C) = + (Temp data) * 0.125 °C If the Temp data MSB bit D10 = 1 then the temperature is negative and Temp value (°C) = – (2’s complement of Temp data) * 0.125 °C
The Temp table (Table 7) shows examples of the Temp data and value.
Table 7. Temp table
