r5450 - in trunk/gta02-core/docs/ecn: . ecn0014

[werner at docs.openmoko.org]

Author: werner
Date: 2009-08-15 12:16:23 +0200 (Sat, 15 Aug 2009)
New Revision: 5450

Added:
   trunk/gta02-core/docs/ecn/ecn0014/
   trunk/gta02-core/docs/ecn/ecn0014/U4905-circuit.png
Modified:
   trunk/gta02-core/docs/ecn/STATUS
   trunk/gta02-core/docs/ecn/ecn0014.txt
Log:
- ECN0014: added motivation and replacement part number
- ECN0014: added Joerg's BQ24314DSG design



Modified: trunk/gta02-core/docs/ecn/STATUS
===================================================================
--- trunk/gta02-core/docs/ecn/STATUS	2009-08-14 23:34:25 UTC (rev 5449)
+++ trunk/gta02-core/docs/ecn/STATUS	2009-08-15 10:16:23 UTC (rev 5450)
@@ -13,7 +13,7 @@
 0011	Edit	Reduce number of varistors on USB_VBUS (C4902, C4909)
 0012	Defer	Add fuse to USB_VBUS
 0013	Defer	Increase rated current of B4902
-0014	Defer	Limit non-ESD overvoltage on USB_VBUS
+0014	Defer	Limit non-ESD overvoltage on USB_VBUS (U4905)
 0015	Discuss	Remove Calypso serial interface on headset (U4401)
 0016	Edit	Remove upper acceleration sensor (U7801)
 0017	Edit	Move Bluetooth module (U2) to main PCB

Added: trunk/gta02-core/docs/ecn/ecn0014/U4905-circuit.png
===================================================================
(Binary files differ)


Property changes on: trunk/gta02-core/docs/ecn/ecn0014/U4905-circuit.png
___________________________________________________________________
Name: svn:mime-type
   + application/octet-stream

Modified: trunk/gta02-core/docs/ecn/ecn0014.txt
===================================================================
--- trunk/gta02-core/docs/ecn/ecn0014.txt	2009-08-14 23:34:25 UTC (rev 5449)
+++ trunk/gta02-core/docs/ecn/ecn0014.txt	2009-08-15 10:16:23 UTC (rev 5450)
@@ -1,7 +1,20 @@
-Limit non-ESD overvoltage on USB_VBUS
+Limit non-ESD overvoltage on USB_VBUS (U4905)
 
 
-To do:
-- issue: broken power supply and such, PMU not very tolerant
-- change U4905 to better part
-- defer since it's not an emergency
+The issue: the highest USB voltage the PMU is specied for is 5.5 V,
+which makes it not very tolerant to USB overvoltage. Excessive USB
+voltage may come from defective power supplies and supplies with
+loose design tolerances, such as car chargers.
+
+The RT9711 only provides overcurrent protection but no overvoltage
+protection. A better choice would be the TI BQ24314DSG:
+http://focus.ti.com/lit/ds/symlink/bq24314.pdf
+
+Joerg Reisenweber has designed a circuit using the BQ24314DSG:
+ecn0014/U4905-circuit.png
+
+Defer this to post-gta02-core since it requires a new part and it's
+not an emergency.
+
+
+Author: Werner Almesberger <werner at openmoko.org>