lm77cimmx-5 National Semiconductor Corporation, lm77cimmx-5 Datasheet - Page 9

• Manufacturer Part Number: lm77cimmx-5
• Description: 9-bit Sign Digital Temperature Sensor And Thermal Window Comparator With Two-wire Interface
• Manufacturer: National Semiconductor Corporation

1.0 Functional Description
Note: Event Interrupt mode is drawn as if the user is reading the part. If the user doesn’t read, the outputs would go low and stay that way until the LM77 is read.
1.4 TEMPERATURE DATA FORMAT
Temperature data can be read from the Temperature and Set
Point registers; and written to the Set Point registers. Tem-
perature data can be read at any time, although reading
faster than the conversion time of the LM77 will prevent data
from being updated. Temperature data is represented by a
10-bit, two’s complement word with an LSB (Least Signifi-
cant Bit) equal to 0.5˚C:
1.5 SHUTDOWN MODE
Shutdown mode is enabled by setting the shutdown bit in the
Configuration register via the Serial Bus. Shutdown mode
reduces power supply current to 5 µA typical. T_CRIT_A is
Temperature
+130˚C
+125˚C
+0.5˚C
−0.5˚C
+25˚C
−25˚C
−55˚C
0˚C
01 0000 0100
00 1111 1010
00 0011 0010
00 0000 0001
00 0000 0000
11 1111 1111
11 1100 1110
11 1001 0010
Binary
Digital Output
FIGURE 3. Temperature Response Diagram
(Continued)
3CEh
0FAh
3FFh
104h
032h
001h
000h
392h
Hex
9
reset if previously set. Since conversions are stoped during
shutdown, T_CRIT_A and INT will not be operational. The
Serial Bus interface remains active. Activity on the clock and
data lines of the Serial Bus may slightly increase shutdown
mode quiescent current. Registers can be read from and
written to in shutdown mode. The LM77 takes miliseconds to
respond to the shutdown command.
1.6 INT AND T_CRIT_A OUTPUT
The INT and T_CRIT_A outputs are open-drain outputs and
do not have internal pull-ups. A high level will not be
observed on these pins until pull-up current is provided from
some external source, typically a pull-up resistor. Choice of
resistor value depends on many system factors but, in gen-
eral, the pull-up resistor should be as large as possible. This
will minimize any errors due to internal heating of the LM77.
The maximum resistance of the pull up, based on LM77
specification for High Level Output Current, to provide a 2
volt high level, is 30K ohms.
1.7 FAULT QUEUE
A fault queue of up to 4 faults is provided to prevent false
tripping when the LM77 is used in noisy environments. The 4
faults must occur consecutively to set flags as well as INT
and T_CRIT_A outputs. The fault queue is enabled by set-
ting bit 4 of the Configuration Register high (see Section
1.11).
DS100136-6
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