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Technical details about nook HD+ charging

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modelworks
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Default Technical details about nook HD+ charging

As an engineer I pulled some info from the datasheet for the chip the nook uses, it may help better understand charging issues.
full datasheet is on the TI site at:http://www.ti.com/lit/ds/symlink/bq24196.pdf

Quote:
USB Timer when Charging from USB100mA Source
The total charging time in default mode from USB100mA source is limited by a 45-min max timer.
If you connect the nook to a low power pc port you will only be able to run the charging for 45 minutes before the charger IC stops. To start it again you have to unplug and re-plug the USB cable. The charge current for a 500ma usb port is about 440ma.


Quote:
The device initiates and completes a charging cycle without software control. It automatically detects the battery
voltage and charges the battery in three phases: pre-conditioning, constant current and constant voltage. At the
end of the charging cycle, the charger automatically terminates when the charge current is below a preset limit in
the constant voltage phase. When the full battery falls below the recharge threshold, the charger will
automatically start another charging cycle.
The device fast charges at 1.5A using the charger and charges at 4.208V to the battery. The bad battery setting is for 1.8V, so if your device battery falls to that level it will not charge because the chip assumes a failed battery. I see this a lot in tablets. Someone stops using the tablet when the charge is 10% or less and then 2 weeks later picks up the tablet and it appears dead. The battery cells have discharged below the limit and now will not charge. The device will consume power even if you power off the device because the charging controller is on 24/7 regardless of any mode except shipping mode which we do not have access to . Fix for dead battery is remove the battery from the tablet, charge on external charger , replace.

Quote:
The USB ports on personal computers are convenient charging source for portable devices (PDs). If the portable
device is attached to a USB host, the USB specification requires the portable device to draw limited current
(100mA/500mA in USB 2.0, and 150mA/900mA in USB 3.0). If the portable device is attached to a charging port,
it is allowed to draw up to 1.5A



if you want the info on your own charge stats just type dmesg in a shell prompt.
data to look for is like this:
Code:
Select Code
<7>[224884.880706] bq2419x_is_vbat_in_range: vbat = 4135000
<7>[224884.881378] bq24196 1-006b: bqSetSYSMIN: 3200
<7>[224884.882019] bq24196 1-006b: adj_fast_ichg_lim: 2036, 240, 2036
<6>[224904.594329] android_usb gadget: high speed config #1: android
<7>[224904.594818] bq24196 1-006b: USB_EVENT_ENUMERATED
<6>[224904.595306] android_work: sent uevent USB_STATE=CONFIGURED
<7>[224904.600708] bq24196 1-006b: INTERRUPT 08=6c, 09=0
<7>[224904.600952] bq24196 1-006b: S: Power Good
<7>[224904.601165] bq24196 1-006b: S: CHARGE STATE = 2 (FAST CHARGING)
<7>[224904.601531] bq24196 1-006b: S: VBUS STATE = 1 (USB host)
<7>[224904.601745] bq24196 1-006b: S: Dynamic Power Management enabled
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Sherip
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I have had a few close calls with my battery. It does not charge if verygreen's or other app that permits the Nook to host other USB devices is active, and in most cases I had accidentally activated it. Since it then refuses to charge when connected to power, its in greater danger of completely depleting. Easily fixed as long as the unit is still operating, but no obvious clue when that's the problem.
 
sandsofmyst
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Also, when you put the power plug in real slow at the nook port, even when the battery is not 100%, it will turn green as if full charged and will no longer show that its charging. Possibly, could be initiated in another way I would think.
HTC sensation 4G | cm11 albinoman ROM - 3/2/14 Workaround for incoming phone calls going to missed (including the swipe issue) with all cm based roms -> http://forum.xda-developers.com/show...&postcount=884 (Longest recorded uptime: 1,060 hours)
Nook HD+ 32 | cm11 emmc official ROM (Longest recorded uptime: 331 hours with much daily use)
....Nook HD+ 16 | (Returned due to random reboots; defective tablet)
 
Tzul
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(Last edited by Tzul; 28th June 2014 at 02:52 PM.) Reason: some corrections
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Quote:
Originally Posted by modelworks View Post
If you connect the nook to a low power pc port you will only be able to run the charging for 45 minutes before the charger IC stops. To start it again you have to unplug and re-plug the USB cable. The charge current for a 500ma usb port is about 440ma.
Interesting about the "low power" port. But I haven't seen one yet. Nowadays, many USB2 ports provide up to 1000 mA without negotiation. Originally, the USB specification required that devices connect in a low-power mode (100 mA maximum) and communicate their current requirements to the host, which then permits the device to switch into high-power mode. But the USB Battery Charging Specification changed that. In recent years I've tested several PC mainboards, and an Xbox 360, all of them provide around 1000 mA on USB2 ports without negotiation.
But the Nook HD+ won't make use of that and limit itself to the 440 mA you mentioned. Why? Because it uses the two data lines (D+ and D-) of the USB connection to detect dedicated USB chargers. If the data lines are shorted, the Nook assumes it's connected to a dedicated USB charger and it will draw up to 2000 mA (about 1880 mA in my measurements). If the data lines aren't shorted, it'll limit to 440 mA no matter if the USB power source could provide more.

Quote:
Originally Posted by modelworks View Post
The device fast charges at 1.5A using the charger and charges at 4.208V to the battery.
From where do you get the 1.5 A? Your own dmesg output says "adj_fast_ichg_lim: 2036, 240, 2036", and as I said, mine charges with around 1.8 A.

Also, the line in the dmesg output that gives away the charging speed isn't "CHARGE STATE". It always reads "= 2 (FAST CHARGING)" when an external power source is connected.
The line "DCP detected" is the real confirmation (DCP = dedicated charging port), and apparently also "VBUS STATE".
"VBUS STATE = 1 (USB host)" means the data lines are NOT shorted => max. current intake is 440 mA
"VBUS STATE = 2 (Adapter port)" means the data lines ARE shorted => max current intake is ~2 A.

Furthermore, keep in mind that power from the external source is prioritized to first supply the system, and then the battery. That is, the battery is charged with the "leftovers". Therefore, if you connect the Nook to a source from which it'll only draw the mentioned 440 mA, and you're continuing to use the tablet, then it can happen that the battery won't be charged, or even will be discharged! If you perform some CPU/GPU intensive tasks on the tablet, its power consumption can easily exceed 440 mA, meaning the tablet will use the external source in combination with the battery to satisfy its hunger.

TL;DR:
  • Nooks will only fast charge on dedicated charging ports, which are recognized by having their data pins shorted. That's more or less standard nowadays for generic USB chargers (USB Battery Charging Specification). However, some chargers still don't meet this requirement, and Apple has their own incompatible standard, naturally.
  • Don't use your tablet if you want to charge it from a low-power source (i.e. USB data connection on the Nook), because depending on the workload, the battery will be charged very slowly or will actually be discharged.
 
modelworks
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(Last edited by modelworks; 2nd July 2014 at 09:47 PM.)
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Quote:
Originally Posted by Tzul View Post
Interesting about the "low power" port. But I haven't seen one yet.
Nowadays, many USB2 ports provide up to 1000 mA without negotiation. Originally, the USB specification required that devices connect in a low-power mode (100 mA maximum) and communicate their current requirements to the host, which then permits the device to switch into high-power mode. But the USB Battery Charging Specification changed that. In recent years I've tested several PC mainboards, and an Xbox 360, all of them provide around 1000 mA on USB2 ports without negotiation.
Read page 19 of the document.

Quote:
From where do you get the 1.5 A? Your own dmesg output says "adj_fast_ichg_lim: 2036, 240, 2036", and as I said, mine charges with around 1.8 A.
I just posted that for people to know the general section not as a specific example.
Page 28 of the document explains why the log may read 2036 but actually be 1.5A
 
Tzul
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(Last edited by Tzul; 3rd July 2014 at 01:27 AM.)
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Quote:
Originally Posted by modelworks View Post
Read page 19 of the document.
Have you read it? It's talking about the USB standard there rather than the bq24196. "If the portable device is attached to a charging port, it is allowed to draw up to 1.5A". That's straight from the USB standard, as the common USB2 connectors are rated for up to 1.5 A. However, B&N have engineered their own proprietary cable and connector and provide a 2 A capable power supply, so that limit doesn't apply.
Also, see Table 2 on the same page. The automatic input current limits are 100 mA, 500 mA, and 3 A. Not 1.5 A.

Quote:
Originally Posted by modelworks View Post
I just posted that for people to know the general section not as a specific example.
Page 28 of the document explains why the log may read 2036 but actually be 1.5A
It would be interesting to open a Nook and take a look what resistor value they used for that safety setting, if they used one at all. As I said before, I've measured currents up to 1.88 A on my Nook HD+ from the official charger, so I seriously doubt they hardwired it to 1.5 A max (and wasted money by providing a 2 A power supply when a 1.5 A one would suffice).

PS: Do you know the power supply dir in the Linux SysFS? Check out /sys/class/power_supply/ and its subfolders (one for each power source). There you can find various virtual files, part of which contain monitoring values straight from the hardware, as read by the driver.
In /sys/class/power_supply/bq27500-0/current_now (or in the file "uevent" which contains a summary of the individual values) you can read the battery charge/discharge current, as measured by the PMU chip. I saw values above 1.7 A there last time I charged and checked. And in order to check, I had to wake up the tablet from standby, of course, meaning that some of the power was spent on running the system rather than charging the battery... All of this paints a pretty clear picture: the device really does fast charge at about 2 A (if you use a suitable power supply and if you let the tablet sleep while charging). Not 1.5 A.
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