LM63CIMA/NOPB National Semiconductor, LM63CIMA/NOPB Datasheet - Page 26

• 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

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In the above equation, η and I
cess that was used in the fabrication of the particular diode.
By forcing two currents with a very controlled ratio (N) and
measuring the resulting voltage difference, it is possible to
eliminate the I
ence yields the relationship:
The voltage seen by the LM63 also includes the I
drop across the internal series resistance of the Pentium 4
processor’s thermal diode. The non-ideality factor, η, is the
only other parameter not accounted for and depends on the
diode that is used for measurement. Since ΔV
tional to both η and T, the variations in η cannot be distin-
guished from variations in temperature. Since the tempera-
ture sensor does not control the non-ideality factor, it will
directly add to the inaccuracy of the sensor.
For the Intel Pentium 4 and Mobile Pentium 4 Processor-M
processors Intel specifies a ±0.1% variation in η from part to
part. As an example, assume that a temperature sensor has
an accuracy specification of ±1%°C at room temperature of
25°C and process used to manufacture the diode has a non-
ideality variation of ±0.1%. The resulting accuracy will be:
T
The additional inaccuracy in the temperature measurement
caused by η, can be eliminated if each temperature sensor is
calibrated with the remote diode that it will be paired with.Re-
fer to the processor datasheet for the non-ideality factor.
3.3.2 Compensating for Diode Non-Ideality
In order to compensate for the errors introduced by non-ide-
ality, the temperature sensor is calibrated for a particular
processor. National Semiconductor temperature sensors are
always calibrated to the typical non-ideality of a particular
processor type.
The LM63 is calibrated for the non-ideality of the 0.13 micron
Intel Pentium 4 and Mobile Pentium 4 Processor-M proces-
sors.
When a temperature sensor, calibrated for a specific type of
processor is used with a different processor type or a given
processor type has a non-ideality that strays form the typical
value, errors are introduced.
Temperature errors associated with non-ideality may be in-
troduced in a specific temperature range of concern through
the use of the Temperature Offset Registers 11
12
The
[e-mail] to further request infor-
mation on our recommended setting of the offset register for
different processor types.
3.4 COMPUTING RPM OF THE FAN FROM THE TACH
COUNT
The Tach Count Registers 46
of periods of the 90 kHz tachometer clock in the LM63 for the
tachometer input from the fan assuming a 2 pulse per revo-
ACC
HEX
= ±1°C + (±0.1% of 298°K) = ±1.3°C
.
user
is
s
term. Solving for the forward voltage differ-
encouraged
HEX
s
are dependent upon the pro-
to
and 47
send
HEX
count the number
an
F
be
×R
e-mail
is propor-
S
HEX
voltage
and
to
26
lution fan tachometer, such as the fans supplied with the
Pentium 4 boxed processors. The RPM of the fan can be
computed from the Tach Count Registers 46
This can 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
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
3.5 PCB LAYOUT FOR MINIMIZING NOISE
In a noisy environment, such as a processor mother board,
layout considerations are very critical. Noise induced on
traces running between the remote temperature diode sensor
and the LM63 can cause temperature conversion errors.
Keep in mind that the signal level the LM63 is trying to mea-
sure is in microvolts. The following guidelines should be fol-
lowed:
1.
2.
3.
Use a low-noise +3.3VDC power supply, and bypass to
GND with a 0.1 µF ceramic capacitor in parallel with a
100 pF ceramic capacitor. A bulk capacitance of 10 µF
needs to be in the vicinity of the LM63's V
Place the100 pF power supply bypass capacitor as close
as possible to the V
diode capacitor as close as possible to the LM63's D+
and D− pins. Make sure the traces to the 2.2 nF capacitor
are matched.
Ideally, the LM63 should be placed within 10 cm of the
Processor diode pins with the traces being as straight,
FIGURE 12. Ideal Diode Trace Layout
HEX
HEX
DD
= Decimal (7 x 256) = 1792.
pin and the recommended 2.2 nF
= Decimal (11 x 16) + 15 = 191
HEX
DD
20057021
pin.
and 47
HEX
.