|ADM1030ARQ||Intelligent Temperature Monitor and PWM Fan Controller|
|ADM1030ARQ Datasheet PDF : 28 Pages |
Table III. Remote Sensor Extended Temperature Resolution
The extended temperature resolution for the local and remote
channels is stored in the Extended Temperature Resolution
Register (Register 0x06), and is outlined in Table XVIII.
Table IV. Local Sensor Extended Temperature Resolution
To prevent ground noise interfering with the measurement, the
more negative terminal of the sensor is not referenced to ground,
but is biased above ground by an internal diode at the D– input.
If the sensor is used in a very noisy environment, a capacitor of
value up to 1000 pF may be placed between the D+ and D–
inputs to filter the noise.
To measure DVBE, the sensor is switched between operating
currents of I and N ¥ I. The resulting waveform is passed through
a 65 kHz low-pass filter to remove noise, then to a chopper-
stabilized amplifier that performs the functions of amplification
and rectification of the waveform to produce a dc voltage pro-
portional to DVBE. This voltage is measured by the ADC to give
a temperature output in 11-bit two’s complement format. To
further reduce the effects of noise, digital filtering is performed
by averaging the results of 16 measurement cycles. An external
temperature measurement nominally takes 9.6 ms.
Digital boards can be electrically noisy environments and care
must be taken to protect the analog inputs from noise, particu-
larly when measuring the very small voltages from a remote
diode sensor. The following precautions should be taken:
1. Place the ADM1030 as close as possible to the remote sens-
ing diode. Provided that the worst noise sources such as clock
generators, data/address buses, and CRTs are avoided, this
distance can be 4 to 8 inches.
2. Route the D+ and D– tracks close together, in parallel, with
grounded guard tracks on each side. Provide a ground plane
under the tracks if possible.
3. Use wide tracks to minimize inductance and reduce noise pick-up.
10 mil track minimum width and spacing is recommended.
Figure 4. Arrangement of Signal Tracks
4. Try to minimize the number of copper/solder joints, which
can cause thermocouple effects. Where copper/solder joints
are used, make sure that they are in both the D+ and D–
path and at the same temperature.
Thermocouple effects should not be a major problem as 1∞C
corresponds to about 200 mV, and thermocouple voltages are
about 3 mV/∞C of temperature difference. Unless there are two
thermocouples with a big temperature differential between
them, thermocouple voltages should be much less than 200 mV.
5. Place a 0.1 mF bypass capacitor close to the ADM1030.
6. If the distance to the remote sensor is more than 8 inches, the
use of twisted pair cable is recommended. This will work up
to about 6 to 12 feet.
7. For really long distances (up to 100 feet) use shielded twisted
pair such as Belden #8451 microphone cable. Connect the
twisted pair to D+ and D– and the shield to GND close to
the ADM1030. Leave the remote end of the shield uncon-
nected to avoid ground loops.
Because the measurement technique uses switched current
sources, excessive cable and/or filter capacitance can affect the
measurement. When using long cables, the filter capacitor C1
may be reduced or removed. In any case the total shunt capaci-
tance should not exceed 1000 pF.
Cable resistance can also introduce errors. 1 W series resistance
introduces about 0.5∞C error.
ADDRESSING THE DEVICE
ADD (Pin 13) is a three-state input. It is sampled, on power-up
to set the lowest two bits of the serial bus address. Up to three
addresses are available to the systems designer via this address
pin. This reduces the likelihood of conflicts with other devices
attached to the System Management Bus.
THE ADM1030 INTERRUPT SYSTEM
The ADM1030 has two interrupt outputs, INT and THERM.
These have different functions. INT responds to violations of
software programmed temperature limits and is maskable
(described in more detail later).
THERM is intended as a “fail-safe” interrupt output that can-
not be masked. If the temperature is below the low temperature
limit, the INT pin will be asserted low to indicate an out-of-limit
condition. If the temperature exceeds the high temperature limit,
the INT pin will also be asserted low. A third limit; THERM
limit, may be programmed into the device to set the temperature
limit above which the overtemperature THERM pin will be
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