mirror of
git://projects.qi-hardware.com/wernermisc.git
synced 2024-11-23 22:44:06 +02:00
31 lines
1.2 KiB
Plaintext
31 lines
1.2 KiB
Plaintext
|
M1pre-rc4 vs. capacitative USB load
|
||
|
|
===================================
|
||
|
|
|
||
|
|
This is a test of how the current-limiting USB power switch in
|
||
|
|
M1pre-rc4 handles a "nasty" capacitative USB load. The worst load
|
||
|
|
identified in previous tests with an M1rc3 with altered reset
|
||
|
|
logic (but no current-limiter) [1] was an iCon i-Creativ.
|
||
|
|
|
||
|
|
[1] http://lists.milkymist.org/pipermail/devel-milkymist.org/2011-December/002488.html
|
||
|
|
|
||
|
|
The M1 was set up in the nominal 5.0 V configuration described in
|
||
|
|
README, which results in a supply voltage that's about 200 mV
|
||
|
|
below what M1 should normally receive:
|
||
|
|
|
||
|
|
Source Input J21/J3
|
||
|
|
------- --------------- ---------------
|
||
|
|
5.00 4.81/4.86/4.90 4.47/4.62/4.72
|
||
|
|
|
||
|
|
The worst drop of the 5 V rail that could be observed in about a
|
||
|
|
dozen hotplug tries was about 450 mV [2]. Note that the probe used
|
||
|
|
in these measurements has a linear error that cause readings to be
|
||
|
|
about 2-3% low (~100 mV in this case), i.e., the lowest voltage
|
||
|
|
was still about 200 mV above the threshold of the reset chip.
|
||
|
|
|
||
|
|
[2] usb-icreativ-50us.png
|
||
|
|
|
||
|
|
The tests above were done with a lab power supply that has very
|
||
|
|
fast current limiting. A test with a 5 V switching power supply
|
||
|
|
similar to the one shipped with M1 showed a reduced drop [3] of
|
||
|
|
only about 350 mV.
|