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ADM1030 Folha de dados(PDF) 10 Page - ON Semiconductor |
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ADM1030 Folha de dados(HTML) 10 Page - ON Semiconductor |
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10 / 29 page  REV. A ADM1030 –10– Table III. Remote Sensor Extended Temperature Resolution Extended Remote Temperature Resolution (�C) Low Bits 0.000 000 0.125 001 0.250 010 0.375 011 0.500 100 0.625 101 0.750 110 0.875 111 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 Extended Local Temperature Resolution (�C) Low Bits 0.00 00 0.25 01 0.50 10 0.75 11 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. LAYOUT CONSIDERATIONS 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. 10MIL 10MIL 10MIL 10MIL 10MIL 10MIL 10MIL GND D+ D– GND 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 Rev. 2 | Page 10 of 29 | www.onsemi.com |
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