1.0 Functional Description

The LM92 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

outside the T

for temperatures which exceed T_CRIT. The lines are pro-

grammable for mode and polarity.

1.1 TEMPERATURE COMPARISON

LM92 provides a window comparison against a lower (T

and upper (T

trip point. A second upper trip point

(T_CRIT) functions as a critical alarm shutdown.

Figure 3

depicts the comparison function as well as the modes of op-

eration.

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

HYST

(T

HIGH

−T

HYST

or

T_CRIT − T

T

T

+T

The Status bits are not affected by reads or any other ac-

tions, and always represent the state of temperature vs. set-

points.

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 LM92 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 tem-

perature goes below T

would stay that way until temperature goes above T

T

be reset. At the end of the next conversion cycle, if the con-

dition is true, it is set again. If not, it remains reset.

Event Interrupt Mode:

User reading part resets output un-

til next condition

″event″ occurs (in other words, output is

only set once for a true condition, if reset by a read, it re-

mains reset until the next triggering threshold has been

crossed). Conversely, if a user never read the part, the out-

put would stay set indefinitely after the first event that set the

output. An “event” for Event Interrupt Mode is defined as:

1.

Transitioning upward across a setpoint, or

2.

Transitioning downward across a setpoint’s correspond-

ing hysteresis (after having exceeded that setpoint).

For example, if a user never read the part, and temperature

went below T

stay 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 tem-

perature must cross above T

again.

In either mode, reading any register in the LM92 restarts the

conversion. This allows a designer to know exactly when the

LM92 begins a comparison. This prevents unnecessary In-

terrupts just after reprogramming setpoints. Typically, sys-

tem 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

other will violate this restriction. To be more specific, with

T

HYST

set to 2 ˚C assume T

equal to, or higher than 60 ˚C this restriction is violated.

1.2 DEFAULT SETTINGS

The LM92 always powers up in a known state. LM92 power

up default conditions are:

1.

Comparator Interrupt Mode

2.

T

3.

T

4.

T_CRIT set to 80 ˚C

5.

T

6.

INT and T_CRIT_A active low

7.

Pointer set to “00”; Temperature Register

The LM92 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 follow-

ing curve. The LM92 registers will reset again when the

power supply drops below the voltage plotted in this curve.

1.3 SERIAL BUS INTERFACE

The LM92 operates as a slave on the Serial Bus, so the SCL

line is an input (no clock is generated by the LM92) and the

SDA line is a bi-directional serial data line. According to Se-

rial Bus specifications, the LM92 has a 7-bit slave address.

The five most significant bits of the slave address are hard

wired inside the LM92 and are “10010”. The two least signifi-

cant 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

Average Power on Reset Voltage

vs Temperature

DS101051-18

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