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ADM1031ARQZ-R7 데이터시트(PDF) 10 Page - ON Semiconductor |
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ADM1031ARQZ-R7 데이터시트(HTML) 10 Page - ON Semiconductor |
10 / 30 page ADM1031 http://onsemi.com 10 Figure 18. Signal Conditioning REMOTE SENSING TRANSISTOR BIAS DIODE D+ D– TO ADC LOW−PASS FILTER fC = 65kHz VDD VOUT+ VOUT– IBIAS IN × I If a discrete transistor is used, then the collector is not grounded, and is linked to the base. If a PNP transistor is used, the base is connected to the D– input and the emitter to the D+ input. If an NPN transistor is used, the emitter is connected to the D– input and the base to the D+ input. One LSB of the ADC corresponds to 0.125 °C, so the ADM1031 can theoretically measure temperatures from –127 °C to +127.75°C, although –127°C is outside the operating range for the device. The extended temperature resolution data format is shown in Table 3 and Table 4. Table 2. Temperature Data Format − (Local Temperature and Remote Temperature High Bytes) Temperature (5C) Digital Output −128°C 1000 0000 −125°C 1000 0011 −100°C 1001 1100 −75°C 1011 0101 −50°C 1100 1110 −25°C 1110 0111 −1°C 1111 1111 0°C 0000 0000 +1°C 0000 0001 +10°C 0000 1010 +25°C 0001 1001 +50°C 0011 0010 +75°C 0100 1011 +100°C 0110 0100 +125°C 0111 1101 +127°C 0111 1111 Table 3. Remote Sensor Extended Temperature Resolution Extended Resolution Remote Temperature Low Bits 0.000°C 000 0.125°C 001 0.250°C 010 0.375°C 011 0.500°C 100 0.625°C 101 0.750°C 110 0.875°C 111 The extended temperature resolution for the local and remote channels is stored in the extended temperature resolution register (Register 0 ×06), and is outlined in Table 27. Table 4. Local Sensor Extended Temperature Resolution Extended Resolution Local Temperature Low Bits 0.00°C 00 0.25°C 01 0.50°C 10 0.75°C 11 To prevent ground noise interfering with the measurement, the more negative terminal of the sensor is not referenced to ground, but 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 can 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 proportional to DVBE. This voltage is measured by the ADC to give a temperature output in 11−bit twos 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, particularly when measuring the very small voltages from a remote diode sensor. The following precautions should be taken: 1. Place the ADM1031 as close as possible to the remote sensing 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 pickup. Ten mil track minimum width and spacing is recommended. Figure 19. Arrangement of Signal Tracks 10MIL GND D+ GND D– 10MIL 10MIL 10MIL 10MIL 10MIL 10MIL |
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