Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).

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.

state of an SMBus communication (SMBCLK and SMBData set High).

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

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 in-

dicates 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 ex-

ceed 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)

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

DS101297-5

FIGURE 2. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)

DS101297-24

FIGURE 3. Printed Circuit Board Used for Thermal Resistance Specifications

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