Datasheet

0.01 0.1 1.0 10 100
CONVERSION RATE (Hz)
400
600
800
1000
1200
140
0
1600
1800
2000
SUPPLY CURRENT (PA
LM86
SNIS114E –DECEMBER 2001–REVISED MARCH 2013 www.ti.com
FUNCTIONAL DESCRIPTION
The LM86 temperature sensor incorporates a delta V
BE
based temperature sensor using a Local or Remote
diode and a 10-bit plus sign ADC (Delta-Sigma Analog-to-Digital Converter). The LM86 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 LM86 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 LM86'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. The remote temperature reading reported is adjusted by subtracting from or
adding to the actual temperature reading the value placed in the offset registers.
CONVERSION SEQUENCE
The LM86 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 31.25ms. Different conversion rates will cause the LM86 to draw different
amounts of supply current as shown in Figure 3.
Figure 3. Conversion Rate Effect on Power Supply Current
THE ALERT OUTPUT
The LM86's ALERT pin is an active-low open-drain output that is triggered by a temperature conversion that is
outside the limits defined by the temperature setpoint registers. Reset of the ALERT output is dependent upon
the selected method of use. The LM86's ALERT pin is versatile and will accommodate three different methods of
use to best serve the system designer: as a temperature comparator, as a temperature based interrupt flag, and
as part of an SMBus ALERT system. The three methods of use are further described below. The ALERT and
interrupt methods are different only in how the user interacts with the LM86.
8 Submit Documentation Feedback Copyright © 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM86