Use the charger in PMIC to charge battery


#1

can we use the charger in the PM8916 to charge the battery and use battery to power up the system? I noticed in the schematic p.15, there is the option to disable buck output and enable battery for 3.7V rail. And also in chapter 8 of hardware manual, the block diagram also shows the option to use battery to power the system and also use the charger. How can we implement this?


#2

To be more specific, what kind of battery pack should we use? And where can we put the battery connector house which is shown as J14 in the schematic?


#3

I would also like to be able to power the system by battery and charge by USB, ideally with the ability to use a battery that does not have ID and THERM capabilities. I saw in the PM8916 Device Specification that these pins can be grounded (THERM only if the software battery temperature feature is disabled, but I have not yet figured out a clean device tree or driver modification to do this). I am using the Android *-3 release from the Qualcomm website. Does this or another release support battery charging?


#4

Hi @enormous and @kinscore

Sorry for taking so long to getting around to answering this. The Short answer is: NO - you cannot use the PM8916 to charge a battery.

The long answer is more interesting.

Every battery pack has different charging requirements which are dependent on a large number of factors. Lets start with the battery chemistry, There is Lithium Ion, and Lithium Polymer, each type has different threshold values for the various charging phases. Then depending on the battery manufacturer’s requirements there are different min and max charging rates in the various phases. Next there is the battery capacity, usually smaller batteries have lower charging rates, and larger batteries have higher rates (but not always), you will find some batteries can charge at 3x their nominal capacity, and others are only 1x. Next is battery temperatures, the acceptable charge rates change dependent on battery temperature. Finally there is the battery housing, if the battery is mounted in a thermally conductive housing you might be able to charge faster than when a insulated housing. Of course if you get the charging rates wrong bad things can happen, the battery could catch fire, or you could ruin the battery internal chemistry and significantly reduce the battery lifespan.

The next issue is the 410c will not run when powered by a 3.7V battery. There is no boost circuitry to boost 3.7V to 5V. The I/O needs 5V (HDMI output, and USB) without I/O the board is kind of useless. Even if you don’t need USB and HDMI, even the Mezzanine boards all need 5V.

Due to all of the battery variables, and the fact that the board can’t run on 3.7V, we elected to not support use of the PM8916 battery charger.

The ‘workaround’ is to use an external battery pack and charger. 7.2V, 11.1V, 12V, and 14V battery packs work really well. This is why the power supply input connector is specified to accept anything between 6.5V and 18V. You can use an external battery pack and whatever charger is supplied with the battery pack.

Full Disclosure: I am an employee of Qualcomm Canada, any opinions expressed in this or any other post may not reflect the opinions of my employer.


#5

@ljking
Do I need some kind of circuit to connect a 12V lead acid battery to DB410c?
Can I connect battery while charging?


#6

Hi @Amit Kumar

12V Lead Acid is fine for powering the DragonBoard 410c. The DragonBoard accepts 6.5V to 18V, a Lead Acid battery is nominally 12V, when fully charged it is 13.8V, and in order to get it charged to 13.8V, most chargers will drive the battery up to 14.4V. All of these voltages are in the DragonBoard 410c’s acceptable power supply range. The answer is YES, you can run the Dragonboard 410c from your 12V battery while charging.

Two things I would caution when using a Lead Acid Battery, first ensure that the battery is connected with the correct polarity. I suspect that the DragonBoard 410c will not last long with the high currents available from a lead acid battery. Second I would recommend an inline fuse, just in case you short the board to the chassis.

Full Disclosure: I am an employee of Qualcomm Canada, any opinions expressed in this or any other post may not reflect the opinions of my employer.


#7

@ljking, Thank you for your answer.

I suspect that the DragonBoard 410c will not last long with the high currents available from a lead acid battery. Due to this I asked,
Do I need some kind of circuit to connect a 12V lead acid battery to DB410c? A circuit to bring current down to 2A?
What is a portable and durable battery solution?


#8

Sorry, VERY bad English on my part. I made this two sentences, it should have all been one sentence. Here is the corrected statement.

first ensure that the battery is connected with the correct polarity, I suspect that the DragonBoard 410c will not last long with the high currents available from a lead acid battery if you connect the battery with reverse polarity.

The Fuse is intended to bring the available currents down to a safe level.

Full Disclosure: I am an employee of Qualcomm Canada, any opinions expressed in this or any other post may not reflect the opinions of my employer.


#9

@ljking,
Because I am a newbie kernel developer and I have not dealt with boards in the past. So, It may be my fault to understand it well. What I understand now,

  1. Polarity should be correct. What is the correct porarity of db410c? Center +ve?
  2. I add a 2A fuse in series.

Basically, I want to connect a UPS battery, which is inside UPS. There is also a big inverter battery.


#10

@ijking,

Just to be sure, one can use the 8916 to charge a battery, correct?


#11

Hi @Wale

Yes and No. Yes the PM8916 is designed to be able to charge a small battery, (like in a cell phone), however it cannot charge large batteries, it cannot charge batteries with voltages higher than 3.7V, it cannot charge chemistries other than lithium ion. As we have seen from the Samsung Galaxy, getting battery charging correct and safe is a VERY difficult problem even when you have almost unlimited resources. Hence we do not enable DragonBoard customers access to the charger in the PM8916. Unless you are an OEM you do not have access to the Code that adjusts the PM8916 charge rates and threshold voltages so, as I said in my original post:

The Short answer is: NO – you cannot use the PM8916 to charge a battery.

With the DragonBoard 410c you need to use an external battery pack and an external charger.

Full Disclosure: I am an employee of Qualcomm Canada, any opinions expressed in this or any other post may not reflect the opinions of my employer.


#12

This is for a class project, in which i’m trying to leverage some of the circuits of the dragon board onto a custom PCB. So, it sounds like I need a special code from Qualcomm to be able to use the battery charger feature (https://www.adafruit.com/products/2011), correct?


#13

Hi @Wale:

I will say it once again:

NO – you cannot use the PM8916 to charge a battery.

You will not be able to change the code necessary to set the charge currents.

If you want to use a 3.7V battery you need to use external battery charger IC on your board design.

Full Disclosure: I am an employee of Qualcomm Canada, any opinions expressed in this or any other post may not reflect the opinions of my employer.


#14

Hi @ljking
I am developing a product with DB410C and need to add a battery.
As you said, the board accepts from 6.5V to 18V, but how many amps?
Do you have a suggestion for a portable battery?
Thank you very much;


#15

Hi @cdvillagra Christopher.

The board power consumption is VERY dependant on what the SW is doing, when idling it is about 100mW, and when everything is running hard (4 cores, and GPU running benchmarks) it gets up to about 4.5 Watts. It also depends on what you have plugged in, the USB ports could be another 5Watts, and although I have never seen a mezzanine that draws max, the spec allows for an additional 12 Watts. I didn’t take into account a monitor if you have one.

Assuming you are not pressing the board too hard and you don’t have power hungry USB devices, lets say about 2 watts. for the purposes of sizing the battery. I used a Tenergy charger and 14.4V battery pack from a hobby RC race car. About 2000mAH at 14.4V gives you 28.8WattHours or about 24 Hours of operation at 2 Watts.

Almost any battery pack will work (7.2V, 9.6V, 12V, 14,4V etc), the size you need depends on how long you need to run the system, and the power drain while you are running he system. You can even use a 12V lead Acid car battery of weight isn’t an issue.


#16

12.18 watts, if you count the 1.8v line, which is very nearly mandatory.


#17

I was rounding :wink:

-Lawrence-
Starting to seriously look for work.


#18

Yeah @ljking, Thanks a lot!
I had already seen about these hobby batteries battery pack from a hobby RC race car, so I will learn more about to apply on project.
Cheers.