LM95214CISD National Semiconductor, LM95214CISD Datasheet - Page 33

• Manufacturer Part Number: LM95214CISD
• Description: SENSOR, TEMP, 4-DIODE, 2-WIRE I/F
• Manufacturer: National Semiconductor

Specifications of LM95214CISD

• Ic Output Type: Current
• Sensing Accuracy Range: ± 1°C
• Supply Current: 0.57mA
• Supply Voltage Range: 3V To 3.6V
• Resolution (bits): 11bit
• Sensor Case Style: LLP
• No. Of Pins: 14
• Svhc: No SVHC
• Temperature Sensing Range: -40°C To +140°C
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

3.0 Applications Hints
The LM95214 can be applied easily in the same way as other
integrated-circuit temperature sensors, and its remote diode
sensing capability allows it to be used in new ways as well. It
can be soldered to a printed circuit board, and because the
path of best thermal conductivity is between the die and the
pins, its temperature will effectively be that of the printed cir-
cuit board lands and traces soldered to the LM95214's pins.
This presumes that the ambient air temperature is almost the
same as the surface temperature of the printed circuit board;
if the air temperature is much higher or lower than the surface
temperature, the actual temperature of the LM95214 die will
be at an intermediate temperature between the surface and
air temperatures. Again, the primary thermal conduction path
is through the leads, so the circuit board temperature will con-
tribute to the die temperature much more strongly than will the
air temperature.
To measure temperature external to the LM95214's die, in-
corporates remote diode sensing technology. This diode can
be located on the die of a target IC, allowing measurement of
the IC's temperature, independent of the LM95214's temper-
ature. A discrete diode can also be used to sense the tem-
perature of external objects or ambient air. Remember that a
discrete diode's temperature will be affected, and often dom-
inated, by the temperature of its leads. Most silicon diodes do
not lend themselves well to this application. It is recommend-
ed that an MMBT3904 transistor base emitter junction be
used with the collector tied to the base.
The LM95214 can measure a diode-connected transistor
such as the MMBT3904 or the thermal diode found in an AMD
processor. The LM95214 has been optimized to measure the
MMBT3904 remote thermal diode the offset register can be
used to calibrate for other thermal diodes easily. The
LM95214 does not include TruTherm™ technology that al-
lows sensing of sub-micron geometry process thermal
diodes. For this application the LM95234 would be better suit-
ed.
The LM95234 has been specifically optimized to measure the
remote thermal diode integrated in a typical Intel processor
on 65 nm or 90 nm process or an MMBT3904 transistor. Using
the Remote Diode Model Select register found in the
LM95234 any of the four remote inputs can be optimized for
a typical Intel processor on 65 nm or 90 nm process or an
MMBT3904.
3.1 DIODE NON-IDEALITY
3.1.1 Diode Non-Ideality Factor Effect on Accuracy
When a transistor is connected as a diode, the following re-
lationship holds for variables V
BE
, T and I
F
:
(1)
33
where:
•
•
•
•
•
•
•
In the active region, the -1 term is negligible and may be elim-
inated, yielding the following equation
In Equation 2, η and I
was used in the fabrication of the particular diode. By forcing
two currents with a very controlled ratio(I
ing the resulting voltage difference, it is possible to eliminate
the I
the relationship:
Solving Equation 3 for temperature yields:
Equation 4 holds true when a diode connected transistor such
as the MMBT3904 is used. When this “diode” equation is ap-
plied to an integrated diode such as a processor transistor
with its collector tied to GND as shown in Figure 9 it will yield
a wide non-ideality spread. This wide non-ideality spread is
not due to true process variation but due to the fact that
Equation 4 is an approximation.
National invented TruTherm beta cancellation technology that
uses the transistor equation, Equation 5, which is a more ac-
curate representation of the topology of the thermal diode
found in some sub-micron FPGAs or processors.
q = 1.6×10
T = Absolute Temperature in Kelvin
k = 1.38×10
η is the non-ideality factor of the process the diode is
manufactured on,
I
I
V
S
f
S
BE
= Forward Current through the base-emitter junction
= Saturation Current and is process dependent,
term. Solving for the forward voltage difference yields
= Base-Emitter Voltage drop
−19
−23
Coulombs (the electron charge),
joules/K (Boltzmann's constant),
S
are dependant upon the process that
F2
/ I
F1
) and measur-
www.national.com
(2)
(3)
(4)
(5)