LM76-NEVAL National Semiconductor, LM76-NEVAL Datasheet - Page 7

• Manufacturer Part Number: LM76-NEVAL
• Description: EVALUATION BOARD FOR LM76-N
• Manufacturer: National Semiconductor

Specifications of LM76-NEVAL

• Sensor Type: Temperature
• Sensing Range: -55°C ~ 125°C
• Interface: I²C
• Sensitivity: ±1°C
• Voltage - Supply: 3.3V
• Embedded: No
• Utilized Ic / Part: LM76
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM76-NEVAL

1.0 Functional Description
The LM76 temperature sensor incorporates a band-gap type
temperature sensor, 13-bit ADC, and a digital comparator
with user-programmable upper and lower limit values. The
comparator activates either the INT line for temperatures out-
side the T
temperatures which exceed T_CRIT. The lines are pro-
grammable for mode and polarity.
1.1 TEMPERATURE COMPARISON
LM76 provides a window comparison against a lower (T
and upper (T
(T_CRIT) functions as a critical alarm shutdown.
picts the comparison function as well as the modes of oper-
ation.
1.1.1 Status Bits
The internal Status bits operate as follows:
“True”: Temperature above a T
those respective bits. A “true” for T
T
“ False”: Assuming temperature has previously crossed
above T
low the points corresponding T
T_CRIT − T
T
T
T
The Status bits are not affected by reads or any other actions,
and always represent the state of temperature vs. setpoints.
1.1.2 Hardwire Outputs
The T_CRIT_A hardwire output mirrors the T_CRIT_A flag,
when the flag is true, the T_CRIT_A output is asserted at all
times regardless of mode. Reading the LM76 has no effect
on the T_CRIT_A output, although the internal conversion is
restarted.
The behavior of the INT hardwire output is as follows:
Comparator Interrupt Mode (Default): User reading part
resets output until next measurement completes. If condition
is still true, output is set again at end of next conversion cycle.
For example, if a user never reads the part, and temperature
goes below T
way until temperature goes above T
the user reads the part, the output would be reset. At the end
of the next conversion cycle, if the condition is true, it is set
again. If not, it remains reset.
Event Interrupt Mode: User reading part resets output until
next condition "event" occurs (in other words, output is only
set once for a true condition, if reset by a read, it remains reset
until the next triggering threshold has been crossed). Con-
versely, if a user never read the part, the output would stay
set indefinitely after the first event that set the output. An
“event” for Event Interrupt Mode is defined as:
1.
2.
For example, if a user never read the part, and temperature
went below T
that way forever if a user never read the part.
However if the user read the part, the output would be reset.
Even if the condition is true, it will remain reset. The temper-
ature must cross above T
LOW
LOW
LOW
HYST
Transitioning upward across a setpoint, or
Transitioning downward across a setpoint's
corresponding hysteresis (after having exceeded that
setpoint).
.
, assuming temperature has previously crossed below
, a “false” occurs when temperature goes above T
.
HIGH
LOW
HYST
or T_CRIT, then the temperature must drop be-
LOW
LOW
HIGH
and T
) in order for the condition to be false. For
then INT would become active. It would stay
then INT becomes active. It would stay that
) trip point. A second upper trip point
HIGH
LOW
window, or the T_CRIT_A line for
+ T
HYST
HIGH
LOW
HYST
LOW
to set the output again.
or T_CRIT is “true” for
is temperature below
(T
+ T
HIGH
HYST
− T
Figure 3
. However if
HYST
LOW
LOW
de-
or
+
)
7
In either mode, reading any register in the LM76 restarts the
conversion. This allows a designer to know exactly when the
LM76 begins a comparison. This prevents unnecessary In-
terrupts just after reprogramming setpoints. Typically, system
Interrupt inputs are masked prior to reprogramming trip
points. By doing a read just after resetting trip points, but prior
to unmasking, unexpected Interrupts are prevented.
Avoid programming setpoints so close that their hysteresis
values overlap. An example would be that with a T
of 2°C then setting T
will violate this restriction. To be more specific, with T
to 2°C assume T
higher than 60°C this restriction is violated.
1.2 DEFAULT SETTINGS
The LM76 always powers up in a known state. LM76 power
up default conditions are:
1.
2.
3.
4.
5.
6.
7.
The LM76 registers will always reset to these default values
when the power supply voltage is brought up from zero volts
as the supply crosses the voltage level plotted in the following
curve. The LM76 registers will reset again when the power
supply drops below the voltage plotted in this curve.
1.3 SERIAL BUS INTERFACE
The LM76 operates as a slave on the Serial Bus, so the SCL
line is an input (no clock is generated by the LM76) and the
SDA line is a bi-directional serial data line. According to Serial
Bus specifications, the LM76 has a 7-bit slave address. The
five most significant bits of the slave address are hard wired
inside the LM76 and are “10010”. The two least significant bits
of the address are assigned to pins A1–A0, and are set by
connecting these pins to ground for a low, (0); or to +V
high, (1).
Therefore, the complete slave address is:
MSB
1
Comparator Interrupt Mode
T
T
T_CRIT set to 80°C
T
INT and T_CRIT_A active low
Pointer set to “00”; Temperature Register
LOW
HIGH
HYST
set to 10°C
set to 64°C
set to 2°C
Average Power on Reset Voltage
0
HIGH
HIGH
0
vs Temperature
set to 64°C. If T
and T
1
LOW
to within 4°C of each other
0
LOW
is set equal to, or
A1
10101518
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HYST
HYST
LSB
A0
S
value
for a
set