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High range sense resistor #40

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prasimix opened this issue Jun 17, 2017 · 2 comments

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@prasimix
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commented Jun 17, 2017

Currently used high range resistor (R65) due to high TCR (75 ppm/°C) cause current drift in CC mode of up to 0.6%. It's simply too small (2512 size) and without additional heatsink its temperature can rise over 40 °C over ambient temperature.
Mentioned current drift could be improved in one of the following ways:

  1. Use power resistor with lower TCR (i.e. below 20 ppm/°C). The problem here is finding such part in 2512 size. For example voltsandjolts suggested very promising CSSH2728FT20L0 (TCR 15 ppm/°C) but it's size is 2728.
  2. R65 value is relatively high (0R020). Cut it e.g. in half (0R010) and increase IC7 gain by x2 possibly could lower current drift to some extent.
  3. Existing PCB has enough space around R65 maybe better approach could be to use two or even three power resistors in parallel. With smarter new layout it could be possible to host much wider resistor too (as one that is suggested under first bullet).
@prasimix prasimix added this to the r5B13 milestone Jul 25, 2017
@prasimix prasimix self-assigned this Aug 14, 2017
prasimix added a commit that referenced this issue Sep 24, 2017
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commented Sep 24, 2017

Existing 0R020 sense resistor R65 is replaced with three R030 in parallel. IC7 gain is also doubled. R63 is decreased to 0R082.

prasimix added a commit that referenced this issue Sep 24, 2017
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commented Sep 24, 2017

BOM now include parts for 1 x R010 or 3 x R030 in parallel.

@prasimix prasimix closed this Sep 24, 2017
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