Date:2011-12-27 07:58:42 (8 years 9 months ago)
Author:Werner Almesberger
Commit:a673d621767f7593763b4c57294a18b49b35811a
Message:m1rc3/usbpwr/: added tests with an unfriendly capacitative load

Files: m1rc3/usbpwr/README2 (1 diff)
m1rc3/usbpwr/usb-icreativ-50us-psu.png (0 diffs)
m1rc3/usbpwr/usb-icreativ-50us.png (0 diffs)

Change Details

m1rc3/usbpwr/README2
1M1pre-rc4 vs. capacitative USB load
2===================================
3
4This is a test of how the current-limiting USB power switch in
5M1pre-rc4 handles a "nasty" capacitative USB load. The worst load
6identified in previous tests with an M1rc3 with altered reset
7logic (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
11The M1 was set up in the nominal 5.0 V configuration described in
12README, which results in a supply voltage that's about 200 mV
13below what M1 should normally receive:
14
15Source Input J21/J3
16------- --------------- ---------------
175.00 4.81/4.86/4.90 4.47/4.62/4.72
18
19The worst drop of the 5 V rail that could be observed in about a
20dozen hotplug tries was about 450 mV [2]. Note that the probe used
21in these measurements has a linear error that cause readings to be
22about 2-3% low (~100 mV in this case), i.e., the lowest voltage
23was still about 200 mV above the threshold of the reset chip.
24
25[2] usb-icreativ-50us.png
26
27The tests above were done with a lab power supply that has very
28fast current limiting. A test with a 5 V switching power supply
29similar to the one shipped with M1 showed a reduced drop [3] of
30only about 350 mV.
m1rc3/usbpwr/usb-icreativ-50us-psu.png
m1rc3/usbpwr/usb-icreativ-50us.png

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