Werner's Miscellanea

Werner's Miscellanea Git Source Tree

1	M1pre-rc4 vs. capacitative USB load
2	===================================
3
4	This is a test of how the current-limiting USB power switch in
5	M1pre-rc4 handles a "nasty" capacitative USB load. The worst load
6	identified in previous tests with an M1rc3 with altered reset
7	logic (but no current-limiter) [1] was an iCon i-Creativ.
8
9	[1] http://lists.milkymist.org/pipermail/devel-milkymist.org/2011-December/002488.html
10
11	The M1 was set up in the nominal 5.0 V configuration described in
12	README, which results in a supply voltage that's about 200 mV
13	below what M1 should normally receive:
14
15	Source Input J21/J3
16	------- --------------- ---------------
17	5.00 4.81/4.86/4.90 4.47/4.62/4.72
18
19	The worst drop of the 5 V rail that could be observed in about a
20	dozen hotplug tries was about 450 mV [2]. Note that the probe used
21	in these measurements has a linear error that cause readings to be
22	about 2-3% low (~100 mV in this case), i.e., the lowest voltage
23	was still about 200 mV above the threshold of the reset chip.
24
25	[2] usb-icreativ-50us.png
26
27	The tests above were done with a lab power supply that has very
28	fast current limiting. A test with a 5 V switching power supply
29	similar to the one shipped with M1 showed a reduced drop [3] of
30	only about 350 mV.
31

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