LM63CIMA/NOPB National Semiconductor, LM63CIMA/NOPB Datasheet - Page 25

• Manufacturer Part Number: LM63CIMA/NOPB
• Description: IC TEMP SENSR REMOTE DIODE 8SOIC
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM63CIMA/NOPB

• Function: Fan Control, Temp Monitor
• Topology: ADC (Sigma Delta), Comparator, Fan Speed Control, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: 0°C ~ 85°C, External Sensor
• Output Type: SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 3.6 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Ic Output Type: Digital
• Sensing Accuracy Range: ± 1°C
• Supply Current: 1.3mA
• Supply Voltage Range: 3V To 3.6V
• Resolution (bits): 11bit
• Sensor Case Style: SOIC
• No. Of Pins: 8
• Termination Type: SMD
• Rohs Compliant: Yes
• Filter Terminals: SMD
• Accuracy %: 1°C
• For Use With: LM63EVAL - BOARD EVALUATION LM63
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM63CIMA; LM63CIMA

3.2 USE OF THE LOOKUP TABLE FOR NON-LINEAR
PWM VALUES VS TEMPERATURE
The Lookup Table, Registers 50 through 5F, can be used to
create a non-linear PWM vs Temperature curve that could be
used to reduce the acoustic noise from processor fan due to
linear or step transfer functions. An example is given below:
EXAMPLE:
In a particular system it was found that the best acoustic fan
noise performance was found to occur when the PWM vs
Temperature transfer function curve was parabolic in shape.
From 25°C to 105°C the fan is to go from 20% to 100%. Since
there are 8 steps to the Lookup Table we will break up the
Temperature range into 8 separate temperatures. For the 80°
C over 8-steps = 10°C per step. This takes care of the x-axis.
For the PWM Value, we first select the PWM Frequency. In
this example we will make the PWM Frequency (Register 4C)
20.
For 100% Duty Cycle then, the PWM value is 40. For 20% the
minimum is 40 x (0.2) = 8.
We can then arrange the PWM, Temperature pairs in a
parabolic fashion in the form of y = 0.005 • (x −25)
We can then program the Lookup Table with the temperature
and Closest PWM Values required for the curve required in
our example.
3.3 NON-IDEALITY FACTOR AND TEMPERATURE
ACCURACY
The LM63 can be applied to remote diode sensing in the same
way as other integrated-circuit temperature sensors. 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 its pins. This presumes that the
ambient air temperature is nearly 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 ac-
tual temperature of the LM63 die will be an intermediate
temperature between the surface and air temperatures.
Again, the primary thermal conduction path is through the
leads, so the circuit board surface temperature will contribute
to the die temperature much more than the air temperature.
To measure the temperature external to the die use a remote
diode. This diode can be located on the die of the target IC,
such as a CPU processor chip as shown in
measurement of the IC’s temperature, independent of the
LM63’s temperature. The LM63 has been optimized for use
with the thermal diode on the die of an Intel Pentium 4 or a
Mobile Pentium 4 Processor-M processor.
Temperature
105
25
35
45
55
65
75
85
95
PWM Value
Calculated
10.0
12.5
16.0
20.5
26.0
32.5
40.0
8.0
8.5
Figure
Closest PWM
Value
10
13
16
21
26
33
40
10, allowing
8
9
2
+ 8
25
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 appli-
cation. It is recommended that a diode-connected 2N3904
transistor be used, as shown in figure
the transistor is connected to the collector and becomes the
anode. The emitter is the cathode.
A LM63 with a diode-connected 2N3904 transistor approxi-
mates the temperature reading of the LM63 with the Pentium
4 processor by 1°C.
T
3.3.1 Diode Non_Ideality
When a transistor is connected to a diode the following rela-
tionship holds for V
where
•
•
•
•
•
•
•
In the active region, the −1 term is negligible and may be
eliminated, yielding the following equation
2N3904
q = 1.6x10
T = Absolute Temperature in Kelvin
k = 1.38x10
η is the non-ideality factor of the manufacturing process
used to make the thermal diode
I
I
V
s
f
be
= Forward Current through the base emitter junction
= Saturation Current and is process dependent
FIGURE 10. Processor Connection to LM63
FIGURE 11. Processor Connection to LM63
= Base Emitter Voltage Drop
= T
PENTIUM 4
−19
−23
Coulombs (the electron charge)
joules/K (Boltzmann’s constant)
be
− 1°C
, T, and I
F
:
Figure
11. The base of
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