LM90CIMMX National Semiconductor, LM90CIMMX Datasheet - Page 7

• Manufacturer Part Number: LM90CIMMX
• Manufacturer: National Semiconductor

Specifications of LM90CIMMX

• Temperature Sensor Function: Temp Sensor
• Interface Type: Serial (2-Wire)
• Output Type: Digital
• Package Type: MSOP
• Operating Temperature (min): 0C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Commercial
• Operating Supply Voltage (min): 3V
• Operating Supply Voltage (typ): 3.3V
• Operating Supply Voltage (max): 3.6V
• Lead Free Status / Rohs Status: Not Compliant

Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: Local temperature accuracy does not include the effects of self-heating. The rise in temperature due to self-heating is the product of the internal power
dissipation of the LM90 and the thermal resistance. See (Note 5) for the thermal resistance to be used in the self-heating calculation.
Note 9: Quiescent current will not increase substantially with an SMBus.
Note 10: This specification is provided only to indicate how often temperature data is updated. The LM90 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: The output rise time is measured from (V
Note 13: The output fall time is measured from (V
Note 14: Holding the SMBData and/or SMBCLK lines Low for a time interval greater than t
SMBData and SMBCLK pins to a high impedance state.
1.0 Functional Description
The LM90 temperature sensor incorporates a delta V
based temperature sensor using a Local or Remote and a
10-bit plus sign ADC (Delta-Sigma Analog-to-Digital Con-
verter). The LM90 is compatible with the serial SMBus ver-
sion 2.0 two-wire interface. Digital comparators compare the
measured Local Temperature (LT) to the Local High (LHS),
Local
user-programmable temperature limit registers. The mea-
sured Remote Temperature (RT) is digitally compared to the
Remote High (RHS), Remote Low (RLS) and Remote
T_CRIT (RCS) user-programmable temperature limit regis-
ters. Activation of the ALERT output indicates that a com-
parison 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 compara-
tor 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 tem-
perature goes below the setpoint calculated by T_CRIT −
TH. The hysteresis register impacts both the remote tem-
perature and local temperature readings.
The LM90 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 LM90’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 non_ideality error,
discussed further in Section 4.1 DIODE NON-IDEALITY .
The remote temperature reading reported is adjusted by
subtracting from or adding to the actual temperature reading
the value placed in the offset registers.
1.1 CONVERSION SEQUENCE
The LM90 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 pro-
cess the busy bit (D7) in the Status register (02h) is high.
These conversions are addressed in a round robin se-
quence. The conversion rate may be modified by the Con-
version 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 LM90 to draw different amounts of
supply current as shown in Figure 2 .
Low
(LLS)
and
Local
IN(1)
IN(0)
T_CRIT
min - 0.15V) to (V
max + 0.15V) to (V
(LCS)
IN(1)
BE
IN(1)
min + 0.15V).
min − 0.15V).
7
1.2 THE ALERT OUTPUT
The LM90’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. Re-
set of the ALERT output is dependent upon the selected
method of use. The LM90’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 de-
scribed below. The ALERT and interrupt methods are differ-
ent only in how the user interacts with the LM90.
Each temperature reading (LT and RT) is associated with a
T_CRIT setpoint register (LCS, RCS), a HIGH setpoint reg-
ister (LHS and RHS) and a LOW setpoint register (LLS and
RLS). At the end of every temperature reading, a digital
comparison determines whether that reading is above its
HIGH or T_CRIT setpoint or below its LOW setpoint. If so,
the corresponding bit in the STATUS REGISTER is set. If the
ALERT mask bit is not high, any bit set in the STATUS
REGISTER, with the exception of Busy (D7) and OPEN
(D2), will cause the ALERT output to be pulled low. Any
temperature conversion that is out of the limits defined by the
temperature setpoint registers will trigger an ALERT. Addi-
tionally, the ALERT mask bit in the Configuration register
must be cleared to trigger an ALERT in all modes.
1.2.1 ALERT Output as a Temperature Comparator
When the LM90 is implemented in a system in which it is not
serviced by an interrupt routine, the ALERT output could be
used as a temperature comparator. Under this method of
FIGURE 2. Conversion Rate Effect on Power Supply
TIMEOUT
will reset the LM90’s SMBus state machine, therefore setting
Current
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