lm95245eb National Semiconductor Corporation, lm95245eb Datasheet - Page 20

• Manufacturer Part Number: lm95245eb
• Description: Precision Remote Diode Digital Temperature Sensor With Trutherm? Bjt Beta Compensation Technology For 45nm Process
• Manufacturer: National Semiconductor Corporation

www.national.com
(Read/Write Address 19h):
Power on Reset default is 6Eh (110°C).
(Read/Write Address 21h):
Power on Reset default is 0Ah (10°C).
2.6 IDENTIFICATION REGISTERS
(Read Only Address FEh): Always returns 01h.
(Read Only Address FFh): Default is B3h. This register will increment by 1 every time there is a revision to the die by National
Semiconductor. The initial revision bits for B3h are shown below.
3.0 Applications Hints
The LM95245 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 LM95245'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 LM95245 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 LM95245's die, use
a remote diode. This diode can be located on the die of a
target IC, allowing measurement of the IC's temperature, in-
dependent of the LM95245's temperature. A discrete diode
can also be used to sense the temperature of external objects
or ambient air. Remember that a discrete diode's temperature
will be affected, and often dominated, by the temperature of
its leads. Most silicon diodes do not lend themselves well to
this application. It is recommended that an MMBT3904 tran-
sistor base-emitter junction be used with the collector tied to
the base. Accuracy using the MMBT3904 is not guaranteed.
For applications requiring the use of the MMBT3904 use the
LM95235.
The LM95245's BJT Beta Compensation TruTherm technol-
ogy allows accurate sensing of integrated thermal diodes,
such as those found on most processors.
128
D7
D7
0
D7
D7
0
1
D6
D6
64
0
D6
D6
0
0
Unsigned Remote T_CRIT Limit - 0°C to 255°C
D5
D5
32
0
D5
D5
0
1
Common Hysteresis Register
Manufacturers ID Register
Revision ID Register
D4
D4
16
16
D4
D4
0
1
20
The LM95245 has been optimized to measure the remote
thermal diode integrated in a typical Intel processor on
45 nm, 65 nm or 90 nm process. Using the Remote Diode
Model Select register the remote inputs must be assigned to
sense a typical Intel processor on 45nm, 65 nm or 90 nm pro-
cess.
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
where:
•
•
•
•
•
•
•
D3
D3
D3
D3
0
0
8
8
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
BE
= Forward Current through the base-emitter junction
= Saturation Current and is process dependent,
= Base-Emitter Voltage drop
D2
D2
0
0
D2
D2
−19
4
4
−23
Coulombs (the electron charge),
joules/K (Boltzmann's constant),
D1
D1
0
1
D1
D1
2
2
BE
, T and I
D0
D0
1
1
D0
D0
1
1
F
:
(1)