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MAX1617MEE Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX1617MEE Datasheet(HTML) 9 Page - Maxim Integrated Products |
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9 / 20 page  9 Remote/Local Temperature Sensor with SMBus Serial Interface MAX1617 Maxim Integrated PCB Layout 1) Place the MAX1617 as close as practical to the remote diode. In a noisy environment, such as a computer motherboard, this distance can be 4 in. to 8 in. (typical) or more as long as the worst noise sources (such as CRTs, clock generators, memory buses, and ISA/PCI buses) are avoided. 2) Do not route the DXP–DXN lines next to the deflec- tion coils of a CRT. Also, do not route the traces across a fast memory bus, which can easily intro- duce +30°C error, even with good filtering. Otherwise, most noise sources are fairly benign. 3) Route the DXP and DXN traces in parallel and in close proximity to each other, away from any high- voltage traces such as +12VDC. Leakage currents from PCB contamination must be dealt with careful- ly, since a 20M Ω leakage path from DXP to ground causes about +1°C error. 4) Connect guard traces to GND on either side of the DXP–DXN traces (Figure 2). With guard traces in place, routing near high-voltage traces is no longer an issue. 5) Route through as few vias and crossunders as possi- ble to minimize copper/solder thermocouple effects. 6) When introducing a thermocouple, make sure that both the DXP and the DXN paths have matching thermocouples. In general, PCB-induced thermo- couples are not a serious problem. A copper-solder thermocouple exhibits 3µV/°C, and it takes about 200µV of voltage error at DXP–DXN to cause a +1°C measurement error. So, most parasitic ther- mocouple errors are swamped out. 7) Use wide traces. Narrow ones are more inductive and tend to pick up radiated noise. The 10 mil widths and spacings recommended in Figure 2 aren’t absolutely necessary (as they offer only a minor improvement in leakage and noise), but try to use them where practical. 8) Keep in mind that copper can’t be used as an EMI shield, and only ferrous materials such as steel work well. Placing a copper ground plane between the DXP-DXN traces and traces carrying high-frequency noise signals does not help reduce EMI. PCB Layout Checklist • Place the MAX1617 close to a remote diode. • Keep traces away from high voltages (+12V bus). • Keep traces away from fast data buses and CRTs. • Use recommended trace widths and spacings. • Place a ground plane under the traces. • Use guard traces flanking DXP and DXN and con- necting to GND. • Place the noise filter and the 0.1µF VCC bypass capacitors close to the MAX1617. • Add a 200 Ω resistor in series with VCC for best noise filtering (see Typical Operating Circuit). Twisted Pair and Shielded Cables For remote-sensor distances longer than 8 in., or in par- ticularly noisy environments, a twisted pair is recom- mended. Its practical length is 6 feet to 12 feet (typical) before noise becomes a problem, as tested in a noisy electronics laboratory. For longer distances, the best solution is a shielded twisted pair like that used for audio microphones. For example, Belden #8451 works well for distances up to 100 feet in a noisy environment. Connect the twisted pair to DXP and DXN and the shield to GND, and leave the shield’s remote end unterminated. Excess capacitance at DX_ limits practical remote sen- sor distances (see Typical Operating Characteristics). For very long cable runs, the cable’s parasitic capaci- tance often provides noise filtering, so the 2200pF capacitor can often be removed or reduced in value. Cable resistance also affects remote-sensor accuracy; 1 Ω series resistance introduces about +1/2°C error. Low-Power Standby Mode Standby mode disables the ADC and reduces the sup- ply-current drain to less than 10µA. Enter standby mode by forcing the STBY pin low or via the RUN/STOP bit in the configuration byte register. Hardware and software standby modes behave almost identically: all data is retained in memory, and the SMB interface is alive and listening for reads and writes. The only differ- ence is that in hardware standby mode, the one-shot command does not initiate a conversion. Standby mode is not a shutdown mode. With activity on the SMBus, extra supply current is drawn (see Typical Operating Characteristics). In software standby mode, MINIMUM 10MILS Figure 2. Recommended DXP/DXN PC Traces |
Similar Part No. - MAX1617MEE_12 |
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Similar Description - MAX1617MEE_12 |
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