Problem with bq24072 Li-ion charger - Everything seems OK, except no charging

Hi Pavan,

It seems like all the signals are ok!

Did you compare your schematic to our EVM? Please send me your schematic for review

In some cases the protection mechanism of the Li-Ion battery prevents the charging. To make sure this is not the problem, please charge the battery with a power supply and measure if the battery is charging.

Thanks

Tahar      

Hi Tahar

I compared schematic with EVM, only difference was in PowerPad, that was floating in our schematic, we shorted that too with GND now from other side of PCB, but not sure if the pad is properly touching the IC at the center. And checked the 3.1V battery, it takes current of 900mA when connected with 4.0V power, checked with few other batteries including Nokia BL-5C, so battery also OK. But still TI power does not seem to work for charging. Schematic included for reference.

2806.bq24072_sch1.doc

Regards

Pavan

R13 shown as 1K, is actually 10K and is optional, used when battery does not have 10K NTC.

Regards

Pavan 

Send waveforms of each of the IC's pins. The thermal pad should be tied to the ground plane.  Not sure if the part is damaged if used with a floating thermal pad.

Hi

As checked by Scope and confirmed with multimeter, the status is as:

While Battery connected

ILIM Pin 12 is same as Vin = 5.28V = EN2 Pin 5

TMR Pin 14 = ISET Pin 16 = Pin 1 = GND (0V) = Thermal PAD

TD Pin 15 = CS Pin 4 = EN1 Pin 6 = GND

Vout = 3.43V and Battery Voltage = 3.16V

When Battery Removed, the square wave on battery pin 2 & 3 is around 1 Hz

Mounted Fresh piece of bq24072, the change is as:

Pin 14 TMR is 2.25V,

Pin 12 ILIM is 0.23V DC with around 1 second pulses of 0.5V / 0.23V after every 3 to 4 seconds, and it repeats

Rest all signals same.

I believe due to 10K NTC, there must be some voltage on TS pin from 75uA source.

Hi Pavan,

Can you please change the IC to a new one and send us some wave forms with and without the battery of the Vbat, Ibat, CHG pin, Vout…etc.

I looked at your schematic, it looks good, but what is the output voltage? What is that resistor at the output pin between the output cap and the OUT pin.    

Thanks!

Tahar

Did you compare the schematic with the EVM?

Hi Tahar

Refer Datasheet bq24072, Page 4,

OUT Pin Voltage Regulation, when VIN > VOUT + VDO(IN-OUT), VBAT < 3.2 V  ==> 3.4V

In actual when battery is removed, the output voltage is 4.4V, not 3.4V as above for Vin = 5.2V.

This is same case for bq24072T, with its NTC resistance mounted as per EVM

What part I am missing here?

Regards

Pavan

Hi Pavan,

Can you try to remove the battery and ground the BAT pin? you should see the output voltage goes to 3.4V.

Tahar