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31 lines
1.2 KiB
Plaintext
31 lines
1.2 KiB
Plaintext
Need to revisit isoSPI biasing.
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Existing (1 mA):
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R267 (and related): 1 kOhm
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R265 (and related): 1 kOhm
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Therefore, existing design makes pulse threshhold 500 mV, whereas theoretical pulse amplitude isn't much higher than this. Need to lower R265 (and related) values to lower amplitude threshhold.
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Manual says they can be 500 uA, which is achieved with:
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R267 (and related): 1.2 kOhm
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R265 (and related): 2.8 kOhm
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However, later in the manual manual:
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Automotive applications have a much higher BCI requirement so the LTC6804 IB is set to 1mA, the maximum power level. The isoSPI system is capable of passing a 200mA BCI test with no transmitted bit errors. The 200mA test level is typical for automotive requirements.
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So we should do 1 mA (max current):
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R267 (and related): 0.6 kOhm
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R265 (and related): 1.4 kOhm
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Requirement to achieve 1.0 mA: R267+R265 = 2 kOhm
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Requirement to achieve 0.5 mA: R267+R265 = 4 kOhm
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Current should lie between these two values. Ideally close to - but not more than - 1 mA.
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Solution:
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0.75 mA:
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R267 (and related): 1.00 kOhm
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R265 (and related): 1.65 kOhm (3k3 || 3k3)
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Add ground plane under isoSPI to reduce noise
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Change R130 to (22 nF || 100 kOhm), to reduce common mode noise. Note that R130 is larger than 0805. |