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31 lines
1.2 KiB
Plaintext
31 lines
1.2 KiB
Plaintext
M1pre-rc4 vs. capacitative USB load
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===================================
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This is a test of how the current-limiting USB power switch in
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M1pre-rc4 handles a "nasty" capacitative USB load. The worst load
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identified in previous tests with an M1rc3 with altered reset
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logic (but no current-limiter) [1] was an iCon i-Creativ.
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[1] http://lists.milkymist.org/pipermail/devel-milkymist.org/2011-December/002488.html
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The M1 was set up in the nominal 5.0 V configuration described in
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README, which results in a supply voltage that's about 200 mV
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below what M1 should normally receive:
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Source Input J21/J3
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------- --------------- ---------------
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5.00 4.81/4.86/4.90 4.47/4.62/4.72
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The worst drop of the 5 V rail that could be observed in about a
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dozen hotplug tries was about 450 mV [2]. Note that the probe used
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in these measurements has a linear error that cause readings to be
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about 2-3% low (~100 mV in this case), i.e., the lowest voltage
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was still about 200 mV above the threshold of the reset chip.
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[2] usb-icreativ-50us.png
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The tests above were done with a lab power supply that has very
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fast current limiting. A test with a 5 V switching power supply
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similar to the one shipped with M1 showed a reduced drop [3] of
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only about 350 mV.
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