Datasheet
q
kT
V
t
=
©
§
¹
·
e
«
«
¬
ª
»
»
¼
º
-1
I
F
= I
S
x
V
BE
K x V
t
RPMRPMFan _2723
1983
000,400,51
_ =
u
=
,
)_(__
000,400,5
_
DecimalCountTachTotal
f
RPMFan
u
=
LM96163
SNAS433D –JUNE 2008–REVISED MAY 2013
www.ti.com
Register 47 (MSB) is 7
HEX
= Decimal (7 x 256) = 1792.
The total Tach Count, in decimal, is 191 + 1792 = 1983.
The RPM is computed using the formula
(2)
where
f = 1 for 2 pulses/rev fan tachometer output;
f = 2 for 1 pulse/rev fan tachometer output, and
f = 2 / 3 for 3 pulses/rev fan tachometer output
For our example
(3)
DIODE NON-IDEALITY
The LM96163 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 circuit board lands and traces soldered to the LM96163'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 LM96163 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 contribute to the die temperature much
more strongly than will the air temperature.
The LM96163 incorporates remote diode temperature sensing technology allowing the measurement of remote
temperatures. This diode can be located on the die of a target IC, allowing measurement of the IC's temperature,
independent of the LM96163's die 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 transistor base emitter junction be used with the collector tied to the base.
The LM96163’s TruTherm BJT beta compensation technology allows accurate sensing of integrated thermal
diodes, such as those found on most processors. With TruTherm technology turned off, the LM96163 can
measure a diode-connected transistor such as the MMBT3904 or the thermal diode found in an AMD processor.
The LM96163 has been optimized to measure the remote thermal diode integrated in a typical Intel processor on
45nm, 65 nm or 90 nm process or an MMBT3904 transistor. Using the Remote Diode TruTherm Enable register
the remote input can be optimized for a typical Intel processor on 45nm, 65 nm or 90 nm process or an
MMBT3904.
Diode Non-Ideality Factor Effect on Accuracy
When a transistor is connected as a diode, the following relationship holds for variables V
BE
, T and I
F
:
(4)
where:
(5)
38 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM96163