maemo.org - Talk - View Single Post - N900 will not allow USB OTG!

	joerg_rw	2010-04-08 , 02:54
	Posts: 2,222 \| Thanked: 12,651 times \| Joined on Mar 2010 @ SOL 3	#673

Originally Posted by blue_led

i think you are wrong

OTG = Boost mode enable control or input current limiting selection pin
...
At POR, the OTG pin is default to be used as the input current limiting selection pin. When OTG = High, Iin – limit = 500mA and when OTG = Low, Iin – limit = 100mA, see the Control Register for details.

so
otg = chgr_det = 1 >> boost on charge , stupid
otg = chgr_det = 0 >> no power , no boost , no host ( 3N )
how hell actually charging is made ? probably isp1707 is disabled by software and through 100k ( R4281 ) resistor otg=low resulting charging is enabled
really, really stupid choice. quick and dirty and overall wrong

My conclusions from these datasheet passages are same like shadowjk's, and I think you need to reread the bq24150 datasheet. Actually from what I remember boost mode will persist *only* if kept alive by cyclic refreshing of 32s I2C watchdog timer. There's no way it could start after PowerOnReset by simply asseting OTG.

BTW I'm not sure 1707 does assert CHRG_DET on sensing voltage on VBUS. For sure this would be kinda stupid, aiui the purpose of the CHRG_DET->OTG connection is like that: 1707 detects charger by sensing D+/- short, asserts CHRG_DET, 24150 switches to 500mA charge mode

Last edited by joerg_rw; 2010-04-08 at 03:00.

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