Control Logic

One Shot

Register

Remote Offset

Registers

Local/Remote

Temperature

Registers

HIGH

Limit

Registers

LOW

Limit

Registers

T_CRIT Limit

& Hysteresis

Registers

Configuration

and Status

Registers

Conversion

Rate

Registers

Two-Wire Serial

Interface

Local/Remote

Diode Selector

Temperature

Sensor

Circuitry

10-Bit Plus Sign

-$

Converter

Programable

Level

Filter

Fault

Queue

Fault

Queue

Fault

Queue

S

R

3.0V-3.6V

D+

D-

T_Crit_A

ALERT

SMBData

SMBClock

Q

LM89

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SNIS128D – AUGUST 2002 – REVISED JUNE 2014

9

Detailed Description

9.1 Overview

The LM89 temperature sensor incorporates a delta VBE based temperature sensor using a Local or Remote

diode and a 10-bit plus sign ADC (Delta-Sigma Analog-to-Digital Converter). The LM89 is compatible with the

serial SMBus version 2.0 two-wire interface. Digital comparators compare the measured Local Temperature (LT)

to the Local High (LHS), Local Low (LLS) and Local T_CRIT (LCS) user-programmable temperature limit

registers. The measured Remote Temperature (RT) is digitally compared to the Remote High (RHS), Remote

Low (RLS) and Remote T_CRIT (RCS) user-programmable temperature limit registers. Activation of the ALERT

output indicates that a comparison is greater than the limit preset in a T_CRIT or HIGH limit register or less than

the limit preset in a LOW limit register. The T_CRIT_A output responds as a true comparator with built in

hysteresis. The hysteresis is set by the value placed in the Hysteresis register (TH). Activation of T_CRIT_A

occurs when the temperature is above the T_CRIT setpoint. T_CRIT_A remains activated until the temperature

goes below the setpoint calculated by T_CRIT

− TH. The hysteresis register impacts both the remote

temperature and local temperature readings.

The LM89 may be placed in a low power consumption (Shutdown) mode by setting the RUN/STOP bit found in

the Configuration register. In the Shutdown mode, the LM89's SMBus interface remains while all circuitry not

required is turned off.

The Local temperature reading and setpoint data registers are 8-bits wide. The format of the 11-bit remote

temperature data is a 16-bit left justified word. Two 8-bit registers, high and low bytes, are provided for each

setpoint as well as the temperature reading. Two offset registers (RTOLB and RTOHB) can be used to

compensate for nonideality error, discussed further in Diode Nonideality. The remote temperature reading

reported is adjusted by subtracting from or adding to the actual temperature reading the value placed in the

offset registers.

9.2 Functional Block Diagram

9.3 Feature Description

9.3.1 Conversion Sequence

The LM89 takes approximately 31.25 ms to convert the Local Temperature (LT), Remote Temperature (RT), and

to update all of its registers. Only during the conversion process the busy bit (D7) in the Status register (02h) is

high. These conversions are addressed in a round robin sequence. The conversion rate may be modified by the

Conversion Rate Register (04h). When the conversion rate is modified a delay is inserted between conversions,

the actual conversion time remains at 31.25 ms. Different conversion rates will cause the LM89 to draw different

amounts of supply current as shown in Figure 4.

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