LM82
Logic Electrical Characteristics
(Continued)
Note 7:
Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8:
The Temperature Error will vary less than
±
1.0˚C for a variation in V
CC
of 3V to 3.6V from the nominal of 3.3V.
Note 9:
Quiescent current will not increase substantially with an active SMBus.
Note 10:
This specification is provided only to indicate how often temperature data is updated. The LM82 can be read at any time without regard to conversion state
(and will yield last conversion result).
Note 11:
Default values set at power up.
Note 12:
Holding the SMBData and/or SMBCLK lines Low for a time interval greater than t
TIMEOUT
will cause the LM82 to reset SMBData and SMBCLK to the IDLE
state of an SMBus communication (SMBCLK and SMBData set High).
10129705
FIGURE 2. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)
10129724
FIGURE 3. Printed Circuit Board Used for Thermal Resistance Specifications
1.0 Functional Description
The LM82 temperature sensor incorporates a band-gap type
temperature sensor using a Local or Remote diode and an
8-bit ADC (Delta-Sigma Analog-to-Digital Converter). The
LM82 is compatible with the serial SMBus and I
2
C two wire
interfaces. Digital comparators compare Local (LT) and Re-
mote (RT) temperature readings to user-programmable set-
points (LHS, RHS, and TCS). Activation of the INT output
indicates that a comparison is greater than the limit preset in
a HIGH register. The T_CRIT setpoint (TCS) interacts with
all the temperature readings. Activation of the T_CRIT_A
output indicates that any or all of the temperature readings
have exceed the T_CRIT setpoint.
1.1 CONVERSION SEQUENCE
The LM82 converts its own temperature as well as a remote
diode temperature in the following sequence:
1. Local Temperature (LT)
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8
2. Remote Diode (RT)
This round robin sequence takes approximately 480 ms to
complete.
1.2 INT OUTPUT and T_HIGH LIMITS
Each temperature reading (LT, and RT) is associated with a
T_HIGH setpoint register (LHS, RHS). At the end of a tem-
perature reading a digital comparison determines whether
that reading has exceeded its HIGH setpoint. If the tempera-
ture reading is greater than the HIGH setpoint, a bit is set in
one of the Status Registers, to indicate which temperature
reading, and the INT output is activated.
Local and remote temperature diodes are sampled in se-
quence by the A/D converter. The INT output and the Status
Register flags are updated at the completion of a conversion,
which occurs approximately 60 ms after a temperature diode
is sampled. INT is deactivated when the Status Register,
containing the set bit, is read and a temperature reading is
NSC [ NATIONAL SEMICONDUCTOR ]
