LM96163C NSC [National Semiconductor], LM96163C Datasheet - Page 36

• Manufacturer Part Number: LM96163C
• Manufacturer: NSC [National Semiconductor]

www.national.com
Also included is programmable hysteresis that is not de-
scribed by the curves of Figure 7. The hysteresis takes effect
as temperature is decreasing and moves all the temperature
set-points down by the programmed amount. For the example
shown here if the hysteresis is set to 1°C and if the tempera-
ture is decreasing from 96.5°C the duty cycle will remain at
68.75% and will not transition to 62.5% until the temperature
drops below 95.5°C.
If at any time the TCRIT output were to activate the PWM duty
cycle will be instantaneously forced to 100% thus forcing the
fans to full on.
The PWM Smoothing Time Intervals table describes the pro-
grammable time interval preventing abrupt changes in the
PWM output duty cycle and thus preventing abrupt acoustical
noise changes as well. The threshold of acoustically detecting
fan noise transition is at about a 2% duty cycle change. The
table describes the time intervals that can be programmed
and the total amount of time it will take for the PWM output to
change from 0% to 100% for each time interval. For example
if the time interval for each step is set to 0.091 seconds the
time it will take to make a 0 to 100% duty cycle change will be
21.6 seconds when the duty cycle resolution is set to 0.39%
or 1.46 seconds when the resolution is 6.25%. One setting
will apply to all LUT transitions.
3.3 COMPUTING RPM OF THE FAN FROM THE TACH
COUNT
The Tach Count Registers 46
of periods of the 90 kHz tachometer clock in the LM96163 for
the tachometer input from the fan assuming a 2 pulse per
revolution fan tachometer, such as the fans supplied with the
Intel boxed processors. The RPM of the fan can be computed
from the Tach Count Registers 46
best be shown through an example.
Example:
Given: the fan used has a tachometer output with 2 per rev-
olution.
Let:
Register 46 (LSB) is BF
and
Register 47 (MSB) is 7
The total Tach Count, in decimal, is 191 + 1792 = 1983.
The RPM is computed using the formula
Time Interval
(seconds)
0.182
0.091
0.046
0.023
PWM Smoothing Time Intervals
HEX
HEX
resolution
(seconds)
w/ 6.25%
= Decimal (7 x 256) = 1792.
2.913
1.456
0.728
0.364
= Decimal (11 x 16) + 15 = 191
HEX
0-100% DC Time
and 47
HEX
HEX
and 47
count the number
resolution
w/ 0.39%
Seconds
HEX
43.7
21.6
10.9
5.45
. This can
36
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
3.4 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 cir-
cuit 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 con-
tribute to the die temperature much more strongly than will the
air temperature.
The LM96163 incorporates remote diode temperature sens-
ing technology allowing the measurement of remote temper-
atures. 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 am-
bient 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 technolo-
gy allows accurate sensing of integrated thermal diodes, such
as those found on most processors. With TruTherm technol-
ogy 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.