BQ24600: Charging is not done with its set charge current

Hi Virednra,

   What is measured VFB voltage, and what is measured battery voltage? Most likely the battery you have inserted is discharged, and BQ24600 is charging in the precharge condition (VFB < VLOWV where VLOWV = 1.55V). The precharge current is fixed 1/10th of the programmed charge current, which is determined by the voltage on the ISET pin.

 Another possibility is if battery is near fully charged, and charging in the CV (constant voltage region) where output voltage is being regulated, and charge current is allowed to taper down.

Hi Kedar,

I am using Li-ion Battery : INR-18650A

Measured VFB Voltage is  = 1.8V

Battery Voltage = 3.662 V

Voltage on high side MOSFET (D)  = 11.9 V    (G) = 5.721V      (S) = 3.73V

Voltage on LOW side MOSFET (D) = 3.73V   (G) = 1.3 V    (S) =  0V

Thanks,

Virendra

Hi Virendra,

   From measured results of SRN and VFB the battery is not in precharge mode. Can you take scope capture of HIDRV, LODRV, PH? If possible to include inductor current waveform, please do as this will be very helpful. Also verify REGN voltage.

Hi Kedar,

Thanks,

Measured REGN voltage = 6.2 V 

Regarding the wave form, due to covid 19, i am working from home so capturing  wave form may take time. i will update you whenever i am able to capture a waveform.

Please look at a schematic attached herewith, let me know if is there any suggestion?

BQ24600_Charger.pdf

Regards,,

Virendra

Hi Virendra,

    I suspect that the switching MOSFETS are not being driven correctly, or that there is some issue with operating in CCM, which is why the charge controller is not able to deliver expected charge current. Once we look at those waveforms we can narrow down root cause from layout, as these issues usually have something to do with grounding of layout or incorrect selection of external components for the switching converter portion of the schematic.

From schematic the BQ24600 portion of the schematic looks fine. Can you tell me the part number for the inductor you are using?

Hi Kedar,

Thanks,

Part No. of Inductor  =  IHLP2525CZET3R3M11     

Make : Vishay-Dale

Part Description :  FIXED IND 3.3UH 7A 26MOHM SMD

Regards,

Virendra

Hi Virendra,

   As BQ24600 has high switching frequency, this reduces current ripple and the inductor saturation current from the datasheet for 3.3uH inductor is sufficiently rated. Next step is to observe the waveforms. You can update this thread when you get the opportunity.

Hi Kedar,

I have captured the waveform of LODRV, HIDRV and PH. Captured waveform are attached herewith.

Regards,

Virendra

Hi Virendra,

    For these captures, are you hitting RUN/STOP on the scope? It looks like some of these signals are overlayed which is not right. Please use edge trigger. Regarding LODRV this waveform does not look right, as the negative undershoot voltage is too high. 

Please recapture these using edge trigger