MAX31723MUA+【PDF 9/15 页】IC THERMOMETER/STAT SPI-3W 8UMAX

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Digital Thermometers and Thermostats

with SPI/3-Wire Interface

Thermostat

The devices thermostat can be programmed to power

up in either comparator mode or interrupt mode, which

activate and deactivate the open-drain thermostat output

(TOUT) based on user-programmable trip points (T

HIGH

and T

LOW

). The T

HIGH

and T

LOW

registers contain

Celsius temperature values in twos complement format

and are stored in EEPROM memory. As such, the values

are nonvolatile and can be programmed prior to install-

ing the devices for stand-alone operation.

The data format of the T

HIGH

and T

LOW

registers is

identical to that of the temperature register (Figure 5).

After every temperature conversion, the measurement is

compared to the values stored in the T

HIGH

and T

LOW

registers. The T

HIGH

locations 03h (LSB) and 04h (MSB), and the T

LOW

reg-

ister is assigned to address locations 05h (LSB) and

06h (MSB). The TOUT output is updated based on the

result of the comparison and the operating mode of the

devices. The number of T

HIGH

and T

LOW

bits used dur-

ing the thermostat comparison is equal to the conversion

resolution set by the R1 and R0 bits in the configuration/

status register. For example, if the resolution is 9 bits,

only the nine MSBs of T

HIGH

and T

LOW

are used by the

thermostat comparator.

If the user does not wish to use the thermostat capa-

bilities of the devices, the TOUT output should be left

unconnected. Note that if the thermostat is not used, the

HIGH

and T

LOW

registers can be used for general stor-

age of system data.

Comparator Mode

When the thermostat is in comparator mode, TOUT

can be programmed to operate with any amount of

hysteresis. The TOUT output becomes active when the

measured temperature exceeds the T

HIGH

value. TOUT

then stays active until the first time the temperature falls

below the value stored in T

LOW

. Putting the devices into

shutdown mode does not clear TOUT in comparator

mode. Figure 6 illustrates thermostat comparator mode

operation.

Interrupt Mode

In interrupt mode, the TOUT output first becomes active

when the measured temperature exceeds the T

HIGH

value. Once activated, in continuous conversion mode

TOUT can only be cleared by either putting the devices

into shutdown mode or by reading from any register

(configuration/status, temperature, T

HIGH

, or T

LOW

)

on the devices. In one-shot mode, TOUT can only be

cleared by reading from any register (configuration/

status, temperature, T

HIGH

, or T

LOW

) on the devices.

Figure 6. TOUT Operation Example

HIGH

LOW

TEMPERATURE

TOUT OUTPUTCOMPARATOR MODE

TOUT OUTPUTINTERRUPT MODE

INACTIVE

ACTIVE

CONVERSIONS

ASSUMES A READ

HAS OCCURED

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