bq51051b stops charge cycle after about ~5sec.

bq51051b stops charge cycle after about ~5sec. Schematic accordingly to appnote section 9.2.1 from www.ti.com/.../bq51051b.pdf

TS = 10k (no NTC function)

Coil might be a missmatch ? (www.digikey.com/.../4702658)
Coil inductance = 12.3µH

Ros = 43.2kOhm (reading other posts and not having the knowledge to do the FOD tuning)

All other components per appnote and specification.

Input?

I calculated C1 and C2 to:

C1 = 206nF
C2 = 305nF

On the PCB I made room for 3 cap's in parallel for C1 and 2 cap's in parallel for C2.

On my first assemble I put:
C1 = 200nF + 6nF + empty
C2 = 300nF + 5nF

But I guess it's not related to my issue since it starts to charge.
Battery is at 3.7V when I start to charge it.

Fredrik,

What is the charge current you are using?

Have you measured the Ls' (roughly the coil inductance when on the TX)?  That will change the C1 to a bit lower as the inductance will rise.  This is not the issue with the causing the charging to stop, but may impact efficiency.  Also, the calculation for C2 is off.  My calculations show approximately 2.1nF.  Finally, I strongly suggest using two 100nF capacitors instead of a single 200nF capacitor.  Since all of the current is going through these capacitors, they will definitely heat up.

If possible, please send plots showing the BAT voltage and the Battery current during the charge process and termination.

Regards,

Dick

Hello Dick!

Thanks for the reply. I will measure it and reply back asap. I think it's set to 800mA as per the appnote. Thanks for the tip on the 2 x 100nF

This is my calculations on those cap's

Coil from TDK www.digikey.com/.../4702658
Ls = 12.3 uH
R = 410 Mohm

C1 = 1 / ( (2pi * 100000)² * 0.0000123) = 206nF
C2 = ( (1000000 * 2pi)² * 0.0000123) – (1/0.000000206) )^-1 = 305nF

Fredrik,

There is an error in your equation for C2.  The equation you have is missing a "(".  Depending on where it's implemented it changes the value.  You have all the right values in the right places.

The correct value from the formula will be about 2.1nF.

Regards,

Dick

Dick,

You are correct. 2.1nF it is. I will replace it. Maybe 1nF + 1nF then for the same reason mentioned above?

Ok so I measured the BAT pin for voltage. Also replace C2 with the suggested 2.1nF using two caps in parallel.
Nothing really happens voltagewise during the chargecycle other than that the !charge pin goes low. So it's not really charging. led is probably driven entirely from the battery..

Tried without a battery as well. Charge led actually is lit for about 10 sec in both cases, not the stated 5. But I guess that is not too important?

Miore tests. Now taping the coil down to the charge pad and positioning it tight centerwise. Actually manage to get charge led kept lit for "ever". Problem still is that voltage across battery keeps dropping as the led discharges the battery. Now current/voltage supplied on the bat pin as expected. is this a RECT issue? The Ros was selected kind of randomly based on the other threads on this community to 43.2k. Rest of resistors per appnote. Will buy some more lipo 3.7 batteries in case the ones Im testing with have issues. Will report back with fresh ones.

Board increases in temperature somewhat ~35-40degrees. Heat most noticeable underneath the bq51051b. 4 vias to large ground poor. should not be an issue?

Tried with a new battery to rule out problematic battery, which I did not really expect. But It still behaves the same way.
Not really sure how to progress from here.

Thinking I might assemble yet another board to see if the problem stays the same.

Fredrik,

Thank you for the details.  

The LED on CHG should not be on unless charging is active.  If it is on, there is a leakage path which may be causing other problems.  The bq51050BEVM-764 schematic ties the LED to RECT.  Either RECT or BAT is okay.  Using the EVM, I tied a resistor / LED string to OUT and even with BAT on, the LED remained off until the charging started.  Both LEDs turned on at the same time, indicating the open-drain CHG pin is the key to the LED on or off.

What transmitter are you using?

Have you looked at the RECT pin?  Look at the bq51050BEVM-764 User Guide for some other tips.  Figure 4 shows RECT during startup.  You can see that when placed on the transmitter, the RECT pin starts to rise and communicates with the TX.  The pulses on the RECT are actually the communication packets.  Once the RECT pin is at the desired voltage, the output turns on.  RECT then goes to approximately the battery level (plus VTRACK as seen in Figure 23 of the datasheet).

Ros is based on the Foreign Object Detection calibration.  It is possible that this is causing an issue, but for now, I don't think that it is.

You did mention you used the application section from the datasheet to configure your design.  For completeness, can you send you schematic?

Regards,

Dick

Thanks Dick for the ongoing support, much appreciated!

Looking at Section 9.2, Typical Application on

The led is tide from BAT to !CHARGE. But as you stated, not a problem.

The transmitter is a Samsung EP-PA510B, QI compliant.

Output Current:1000 mA

Schematic wise:

I might have a problem on the RECT pin, only one cap of 10uF instead of suggested two 10uF+0.1uF ..... Was to quick to layout the board. Also missing a cap on the BAT as well....  only a 1uF, missing the suggest 0.1uF...

The Boot (10nF) ,Clamp (0.47uF) and Comm(22nF) caps are per appnote.

TS is tide to 10k resistor to ground.

Fredrik,

The LED to CHG can be either RECT or BAT, no problem either way as you noted.

What is the voltage rating of the capacitors touching the AC1/AC2 pins (including BOOT, CLAMP, COMM)?  These should be 25V minimum.

You do note that TS is 10k to ground.  This is very important.

The additional capacitance on RECT and BAT is important for transients and, I'm sure you agree, is not related to this issue.

For a quick look, you can always solder extra capacitors on top of the capacitors in place.

If you get a good look at RECT, this may help us with the next steps.  And, determine why the LED is on when only BAT is applied.

Regards,

Dick

Dick,

I might have been unclear, the led is not on when only bat is applied. Only when placed on the charging pad.
I went and bought yet another charger from Samsung (different model) EP-PG900IBEGWW.

This one came with a wallplug usb 2amp. Looked at the one I was using, it was only a 1amp one. This appears to be the reason the charge cycle ends. Now it's continously on charge when placed on the charge pad. Thats good.

I have been monitoring the voltage on BAT for a while and it slowly decreasing. Only load is the led.

Voltage spec on all caps are 25V

Not sure what to do with rect. Will have a look in the pdf and read up on this.

Placed a probe on rect for about 30 sec.
The slope is from when I removed the probe.

Rect = Green (~4.02V)
Bat = Yellow (3.827V)

Fredrik,

Good news on the 2A charger.  RECT is simply the rectified voltage coming from the AC1/AC2 lines.  RECT is the voltage that is controlled internally (through communication with the TX).  There is really nothing special that you need to do - except for the capacitors.

The RECT plot you have shows RECT just above BAT (about 275mV) which is where it should be.

Based on this, the BAT voltage should rise over time as the battery is charged - not be depleted like it seems yours is.  That indicates to me that the charge current is not making it to the battery somehow.  How long did you run the system?

Can you measure the current into the battery?

We don't have a good curve of the charge cycle in the bq51050B datasheet, but if you look at the bq25100 datasheet you'll see a good plot in figure 18.  It shows what you should see from BAT/Battery and IBAT. 

Regards,

Dick

Slow progress.... But.. progress :-)

Looking at the PDF pages section 8.3.2 and power transfer. If there is any shutdown condition based on EN1/EN2 , TS/CTRL, AD  The RX will ask the TX to shutdown immediately. Since I have a green light it states in the TX manual that it is transmitting power. So therefor I shouldn't have any issue with those pins... correct?

I will look into measuring bat current. Need to create something to connect inbetween...

I ran my tests for about an hour.

Transmitting power is good, but it doesn't really tell the whole story.  We're looking for how much power.  If you could determine the power into the TX, that would help as well.  I am not suggesting it, but what I've done is take the adapter cord apart and use a power supply. That way I can see the TX current.  Based on how much current is there, you can determine approximately how much the RX is using.  Depending on the setup, you can figure 60% to 70% efficiency.  Could be lower.  

If you see input current of about 1.2A with 800mA into the battery.  If you see100-200mA, then you have no current into the battery and something else is amiss.

I generally use a current probe on the oscilloscope for current so I can see any transients.  Additionally, I've done a small sense resistor and measure the voltage across the resistor (two probes possibly).

Regards,

Dick

Dick, great tip!
My lab supply does have current measurement... I have usb-A connectors. I will hook the TX up tomorrow! Thanks for all your help today!

I'm starting to questioning my soldering. What would happen if AD pin is not connected to ground? But It would still require V-ad-pres to disable the bat pin. And it's not really disabled since the led lights up without the battery...

Looks like all pins are soldered nicely from what I can tell. I made the mistake of going small straight away. no TP's...
Double checked all resistor values and also measured ....

Soldered a USB-A connector on a protoboard and hooked up my lab-supply. 5.2V and 2amp's as per the backside of the samsung chargepad. Strange thing, the charge led never came on even though the TX indicated it was on. Current was on off (up/down) maxed at 210mA.

Hello Dick!

Continue reading the pdf and get a bit confused on this calculation.

It states that RILIM = R1 + RFOD on page 20.

To me it looks like the text recommend setting RFOD = 200 and R1=205  which results in RILIM=393
Not really inline with the formula on page 20 section 8.3.4.3.1??
 

Still no current flowing to the battery.

Fredrik,

You are correct that the numbers in 9.2.1.2.3 are incorrect.  RILIM = R1 + RFOD is the correct equation.  So, if RILIM = 393 (from RILIM = KILIM/ILIM: 314/800mA) and RFOD = 200, then R1 = 393-200=193 (not the 205 shown in the datasheet discussion).

Choosing 205 for R1 would yield:  ILIM = 314/(200+205) = 775mA.  

If the CHG pin is still active (LED on) then the bq51050B recognizes that a battery is present and is trying to charge.  Would you be able to use a source meter in place of a battery?  I set the voltage level to 3.5V and set the current limit to about 10% greater than the expected charge current.  This will allow us to see exactly how much current is going into the system.  Without a voltage on the BAT pin, the output won't turn on.

Regards,

Dick

Hi Dick,

No unfortunately I dont have a source meter.

Today I decided to assemble a second board. This time I tripple checked values and ratings while assembling the board.

I made a pass with the multimeter verified what I could (all expect the vqfn package). Looks good to me.
Board behaves pretty much the same way. The led goes on even without a battery while placed on the chargepad (as do the first board).

What I also realize going over everything a .... forth time.. Is that EN2 is floating on my board. Probably not good....
I missed this one totally. Problem is that I was initally thinking of breaking it out to one of my castellated pins since this is a piggyback-board.
So I need to put a pullup resistor to sort it out? Not sure I can "pull this" off :-) on this board....

From PDF:
Input high threshold for EN2 1.3V

What would I pull it up to? Rect? or Bat? or what?

Could this be the reason for my current problem?

Fredrik,

EN2 has an internal pull-down which would enable wired charging if present.  Since AD is tied low, wireless power is enabled.  In general, I don't like floating pins even with an internal pull-down.  But, I do not believe this is causing your issue.  The EN2 pin can be left high, low or floating in this case.  I have verified all in the lab.  The only difference for EN2 functionality is the AD bypass.  

Please confirm that AD is tied to ground.

You said " The led goes on even without a battery while placed on the chargepad".  If LED is tied to BAT and the LED is on, the BAT is enabled.  But, without a battery, it will turn off.  I'm not sure why you are getting power there.

Please send a copy of your schematic so I can look a bit more at it.

Regards,

Dick 

1325.ReceiverChargerPowerLatchRoundEurocircuit_revD_newlayout.sch

Dick,

AD is tied to ground. And I have attached the schematic file (Eagle). Thanks for taking the time!
The board contains both the Wireless receiver + charger as well as a software controlled latching circuit.

The board breaks out (not that it matters):

BAT, LATCHED_POWER,GND, POW_SWITCH, CONTROLLER_PIN

I fill the three vias underneath the TI chip before reflowing.

Graph of RECT (green) and BAT (yellow)
RECT probe was attached manually during the collection and was flat at ~4.56V all the time.

Fredrik,

The schematic looks good.  A couple of comments.  That is a very small board.  My first concern would be thermal heating causing some issues.  Not sure how long it would take to cause an issue (and shut down - if it was too high). The voltage level of the capacitors did not show up on my viewing.  Please make sure the AC1, AC2, BOOT, CLAMP and COMM caps are 25V minimum.

With the battery at zero volts, the LED should be off.  Is it?  Or, do you have an offset on the plot?

Another option you have is creating a battery emulator like is shown in the bq51050BEVM-764 user guide.  See figure 3.  It's relatively simple to build.  A couple of high power resistors and a high power diode along with the power supply.

Regards,

Dick

Dick,

Thanks for reviewing the schematics!
All those caps are 25V. Verified!
The led is on when there is no battery connected. It's pulsing abit.

Maybe I have to go down the emulator route. I did have some questions earlier reading that document but I might get back on that when they arise again later on.

Thanks for your support and I will order parts for emulator and assemble a third board in the mean time. I have ordered even better parts (1% 50V) for the important caps. Today some are +-5%. Not sure how that plays out.
Trace width's is per layout guide section. Maybe 3 vias are too little underneath the bq51051b? The board does not get particularly warm. Large groundpoor underneath. Dont have flircamera to measure that but...

Fredrik

Hello Dick,

Got the parts for the emulator and assembled a protoboard. But I'm not sure we are on the same page as to what the problem is.

I'm seeing out/bat pin activated even though the battery is not even connected. All my boards behave this way.
I could go down the route of ordering a flir camera to look a heat buildup but there is no heat from what I can tell touching the board.

Been looking at the layout suggestion to understand what could cause issues like this. I think I'm adhering to most of them.
All my boards have voltage rating of atleast 25V for those caps you mention. And the others are per specification acc. to the pdf.


Any last tip before I give up on this one :-) ?

Fredrik,

It is not time to give up.  I will contact you offline to continue the discussion.

Regards,

Dick