BQ24600 Not Charging over 6A

Hi David,

Thx for answering my message.

today i wanted to try again but now the charger refuses to charge more than 2A... the battery is charged about 60% so i suppose its not in voltage regulation phase.

I will try to discharge it again to see if that is the issue.

How do i check if my IC is not entering thermal regulation?

I dont think my adapter is crashing as i bought a 12,5A 28V 350W supply (SHP350PS28)

www.digikey.be/.../4488609

i could put a verry big capacitor on the output of my adaptor to see if it helps him.

This is a link to my charging schematic

www.dropbox.com/.../Screenshot 2016-09-22 11.20.34.png

HI David,

Your post has helped me a lot and I will be answering inline in red.

I have made some measurements in the following conditions

Ichg = 1,7A               Vsup=28,9V              Vbatt= 22,94V (40%)

That is strange that it now charges lower. Using a 10mOhm sense resistor should be adequate.

I am now using a slightly smaller Rsense to boost the current.

Rsense = 6mOhm

Ichg = Viset/(20*Rsns)

I see what you are doing with the /pg pin. There are 2 ways that the IC will regulate thermal performance:

1) there is a temperature comparator built in to the IC. This will automatically shut down the IC if it senses that the IC is >145 degrees C

Is the IC getting hot to the touch? There are many ways that you can measure the temp of the IC. If it is hot to touch, you could use something as simple as a thermometer they sell at your local store (not very accurate at all, but gives you an idea), some multi meters have thermistor attachments (may be pricey, but if you can find one good), or IR thermal camera (also good, could be pricey). I am sure there are other ways.

I have put my finger on the IC and it was just too hot to stay on it so I measured with my multimeters thermometer. I also measured some other components who are getting hot

IC=50°

Q5= 50°         Q6=70°          L1&L2=50°   R9=36°

I have to say I remember those components where about 100° when I was still able to have Ichg=6A.

2) the external thermistor comparator. This is set at the TS pin. You can measure this voltage. If it the voltage is 73.5% of Vref, it will assume the battery is cold and regulate charge current accordingly. If it is ~37% of Vref, the IC will read that the battery temp is "hot", and similary regulate charge current.

TS=1,63V                   Vref=3,289V

Link to Scope (Vsupp in RED 10V/div  -  Vref in blue 1V/div)

https://www.dropbox.com/s/evztp3jn6qv9agq/Screenshot%202016-09-22%2019.28.41.png?dl=0

Link to Scope (Vsupp in RED 10V/div  -  TS in blue 1V/div)

https://www.dropbox.com/s/k7b1qjbc22wqfgx/Screenshot%202016-09-22%2019.29.45.png?dl=0

I am also curious about the ISET pin. I want to make sure you are not exceeding 2 volts . I am sure you saw this, but your charge current is set by:     Ichg = Viset/(20*Rsns).

Iset=0,582V

Link to Scope (Vsupp in RED 10V/div  -  Iset in blue 1V/div)

https://www.dropbox.com/s/v1sptrr2mt2jocz/Screenshot%202016-09-22%2019.26.01.png?dl=0

This means that charge current is not strictly a function of your sense resistor, and that fluctuations in Viset will also cause fluctuations in Ichg. Can you double check to make sure that it is not causing problems? Scope traces (if you have one available, it is ok if you do not) of Viset and Ichg would be helpful, but not required. I am curious if the digital resistor is causing problems.

I am not using the digital resistor for the moment I had a solder jumper to choose between manual potentiometer and digital resistor. I am now debugging with the manual potentiometer.

Is there any chance you can measure the voltage of your input? If it is crashing, you should be able to see the voltage drop when pg lights up. It looks like the powersupply is more than up to the job (if it is up to spec, every once in awhile it happens that it does not meet spec). Is there an adjustable current limit on the supply?

Vsup=28,9V 

Link to Scope (Vsupp in RED 10V/div  -  Vbatt in Blue 10V/div)

https://www.dropbox.com/s/5rjgfj8y4ofnvbt/Screenshot%202016-09-22%2019.25.11.png?dl=0

Thank you!

I hope these mesurements help to find the issue

Stanislas

Stanislas,

Thank you for the scope shots, those are actually very helpful.

It looks like your 28V supply slides down to about VBAT, which puts the bq24600 in sleep mode. When the device is in sleep mode, npgood will be pulled high indicating that the adapter is not valid. We can verify this if you can get a scope shot of Vsup and Vbat together, and then Vsup and the /pgood pin (or the second stage of your inverter, that will give the same signal since it is inverted twice) together.

The real question then becomes why is your input voltage sliding down like that? We can try to set the charge current low (maybe 1 A, or 0.5 A), and then work up to see if the power supply does not regulate up to spec (or has adjustable current limit - I have accidentally done that to myself before). We can also look for shorts. Do you have any way of measuring input current to see if the charger is pulling more current than expected?

Other places that are "modifications" and could introduce problems are the relay circuit. Can we try just battery to see if that is where the issue is? I notice you are also using two inductors in parallel - I doubt this is the problem but we can keep it in the back of our minds

Hi David,

There is a scope shot where you see Vsup and Vbat together!

Link to Scope (Vsupp in RED 10V/div  -  Vbatt in Blue 10V/div)

https://www.dropbox.com/s/5rjgfj8y4ofnvbt/Screenshot%202016-09-22%2019.25.11.png?dl=0

I did not find any current limitation on my power supply...

On 1Amp it charges perfectly.

I have now added small heat sinks with thermal paste on the Coils and Fets ( L1&L2 and Q5 & Q6) 

Since i have done so i am now able to charge at 5 AMP!!

Allso i did not pay particular attention on how i routed my groundplane. The groundplane is basicly a polygonpour on the bottom layer of my PCB

At this point im verry confused.

Thank you for helping me out :)

Stan

Stanislas,

Oops- you  are correct! That was even the trace I was looking at when I thought I should ask for it.

Hm... that is strange. It is working happily at 5A?

I do have another idea - can I get a scope shot of high drive/low drive together, and then low drive/ Vsupp or npgood?

I am wondering if you are getting capacitive coupling turning on your low fet and high fet at the same time. If they overlap, then your power supply basically shorts to ground and you get shoot through. That may explain why your power supply voltage drops, as well as any overheating since that results in excess power dissipation.

You deed to Use a 22.2V changer to charge a 6s lipo battery, and it will get over 6 Amp, it  is the best way.

Hi Andrew,

What is the input voltage and battery voltage on the PCB board when you used 20AWG cable? 

BTW, What is the unsolved problem currently?

Thanks!,

Alen Chen 

Input voltage (to charger) 28VDC. Battery voltage around 19V.

The (now solved) problem was that I was not able to charge over about 1A. When attempted, the device would switch on and off which I could tell from the PG led blinking.

Turns out there was a good amount of inductance and resistance in the thin wire I was using that limited the inrush of current...

> Andrew