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Today's Topics:
1. Re: Openmoko Bug #2310: charging N900 with gta02 causes the
gta02 to overheat (Openmoko Public Trac)
2. Re: Openmoko Bug #2310: charging N900 with gta02 causes the
gta02 to overheat (Openmoko Public Trac)
--- Begin Message ---
#2310: charging N900 with gta02 causes the gta02 to overheat
-----------------------------+----------------------------------------------
Reporter: lindi | Owner: openmoko-kernel
Type: defect | Status: new
Priority: normal | Milestone:
Component: System Software | Version: unspecified
Severity: normal | Keywords: battery pmu charging
Haspatch: 0 | Blockedby:
Estimated: | Patchreview:
Blocking: | Reproducible:
-----------------------------+----------------------------------------------
Comment(by lindi):
Some comments from IRC:
< DocScrutinizer> lindi-: could you check USB_FLT aka GPM5 GPIO
< DocScrutinizer> maybe AAT1276 does no current limiting but simply
triggers USB_FLT. Maybe we have a short on datalines. Maybe we have
massive drop of efficiency on choke getting satturated and thus all the
current runs into that choke and heats it up (i prefer that idea for now)
< PaulFertser> DocScrutinizer-8: btw, i would be amazed to know N900
actually can draw more than 500mA without negotiating.
I have not removed the main can yet so I can not investigate what damage
might have occured to the components. I also can not measure USB_FLT since
I don't have the N900 anymore to test with.
--
Ticket URL: <https://docs.openmoko.org/trac/ticket/2310#comment:5>
docs.openmoko.org <http://docs.openmoko.org/trac/>
openmoko trac
--- End Message ---
--- Begin Message ---
#2310: charging N900 with gta02 causes the gta02 to overheat
-----------------------------+----------------------------------------------
Reporter: lindi | Owner: joerg
Type: defect | Status: assigned
Priority: normal | Milestone:
Component: System Software | Version:
Severity: major | Keywords: usb hostmode U4904 L4901 hw
heat USB_FLT
Haspatch: 0 | Blockedby:
Estimated: | Patchreview:
Blocking: | Reproducible:
-----------------------------+----------------------------------------------
Changes (by joerg):
* keywords: battery pmu charging => usb hostmode U4904 L4901 hw heat
USB_FLT
* owner: openmoko-kernel => joerg
* version: unspecified =>
* status: new => assigned
* severity: normal => major
Comment:
Replying to [comment:5 lindi]:
> Some comments from IRC:
>
> < DocScrutinizer> lindi-: could you check USB_FLT aka GPM5 GPIO
oops, that's GPG10 of course, and /USB_FLT, so low/0 should indicate a usb
current of >500mA (the limit set by R4918=14k).
From AAT1275 datasheet:
>>
Operation in Current Limit
When a heavy load is applied to OUT2 of the
AAT1275, the load current is limited to the value of
ILIM (determined by RSET) causing a drop in the
output voltage. This increases the AAT1275 power
dissipation and die temperature. When the die tem-
perature exceeds the over-temperature limit, the
AAT1275 shuts down until it has cooled sufficiently,
at which point it will start up again. The AAT1275
will continue to cycle on and off until the load is
removed, power is removed, or until a logic low
level is applied to the EN pin.
A fault flag indicates when the OUT2 pin load cur-
rent has exceeded the current limit level set by
RSET. The fault flag is an active low, open-drain pin
<<
So that suggests the normal way for U4904 to handle overload on USB output
is to heat up to a temp that easily might make the device emit smell.
For sake of component stress kernel should disable EN_USBHOST on detection
of /USB_FLT, as well as raise some warning signal, both in syslog and
events/sysfs
Nevertheless for L4901 the BOM says:
>> INDUCTOR 2.2uH 10% 7.96MHZ 800mA SMT0805 PLL201212F2R2K SUBARU FOR GSM
LR
it seems this maybe doesn't exactly match the considerations for inductor
component selection as found in "Selecting the Boost Inductor"
(AAT1275.pdf, p.11 + p.15) regarding Ipp and saturation.
Alas I wasn't able to find any datasheet for this inductor :-/
So the jury is still out on that one. If the inductor gets saturated on
high loads, this might easily result in massive increase of input current
and heating up of the inductor itself.
A final note on current_now: this is the total of current taken from the
battery cell, including CPU, backlight, and GSM modem. The function of
AAT1275 is to take a low voltage/high current on input, and convert this
to a higher voltage at lower current at output. So even the consumption of
AAT1275 is far beyond the 500mA it can provide for output -> Iin = Iout *
Vout / Vin / Const(efficiency) [0.5 * 5 / 3.6 / 0.8(guess) = 0.87A]
--
Ticket URL: <https://docs.openmoko.org/trac/ticket/2310#comment:6>
docs.openmoko.org <http://docs.openmoko.org/trac/>
openmoko trac
--- End Message ---
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