BQ24650 output voltage problem

Hi,

I have built the circuitry of BQ24650 Li-ion battery charge controller by referring to the article sluu - 444a. The output of this module consists of 2 pins namely :

System Out Voltage and Battery out Voltage.

I am receiving the correct output at the system out voltage pin which has to be according to the input supply provided. But I am not getting the output at the battery out pin. The voltage at this pin should be 12.6 Vdc (as per the design) .

Also I am not getting the voltage at the MPPSET pin which has to be 2.1 Vdc minimum. I have tested all the components and they are working fine. Kindly help me out with this problem.

Thanks and Regards

Make sure the MPPT pin is above 1.2V.

Make sure the voltage on the TS pin is within the range listed in the spec table in the data sheet.

If you capture, with a scope, all the waveforms on each of the pins of the IC (preferably 4 per plot).  I may be able to see what the issue is.

Respected sir,

Here are the waveforms at each pin of the BQ24650 IC:

Pin 1: Vcc

Pin 2: MPPSET - voltage = 1.3V

Pin 3: STAT 1

Pin 4: TS - Voltage = 2.80 V

Pin 5: STAT 2

Pin 6: VREF

Pin 7: TERM_EN

Pin 8: VFB

1) with battery:

2) without battery:

Pin 9: SRN with battery

Pin 10: SRP with battery

Pin 10: Ground

Pin 11: REGN

Pin 13: LODRV

Pin 14: PH

Pin 15: HIDRV

Pin 16: BTST

Please find the schematic of the circuit :

Kindly guide me through the problem.

Thanks and Regards.

Respected sir,

Thank you for your kind inputs. But I am still unable to understand what do I do exactly? Please guide me in this regard.

Thanks and Regards,

Respected Sir,

As per your advice, I have connected a 10K Thermistor in between TS and Ground pin. The voltage at TS pin is observed at 1.8V , the voltage at MPPSET pin is exactly 1.2V . Also, the voltage at SRP pin is 3.7 volts and the voltage at SRN pin is found to be at : 2.9 V when the circuit is connected to to a battery load of 4.1 V 8Ah capacity.

And, the voltage at REGN pin is found to be at 3.1 V.  The LED indicators are always off whether the load is connected or not. I guess there is very little current flowing through the circuit. What can be the problem? How can it be solved?

Thanks and Regards

Respected Sir,

As per your advice, I have connected a 10K Thermistor in between TS and Ground pin. The voltage at TS pin is observed at 1.8V , the voltage at MPPSET pin is exactly 1.2V . Also, the voltage at SRP pin is 3.7 volts and the voltage at SRN pin is found to be at : 2.9 V when the circuit is connected to to a battery load of 4.1 V 8Ah capacity.

And, the voltage at REGN pin is found to be at 3.1 V.  The LED indicators are always off whether the load is connected or not. I guess there is very little current flowing through the circuit. What can be the problem? How can it be solved?

Thanks and Regards

Make sure you test with a lab supply that can supply all the power needed.

Adjust your MPPT divider so that it reads >1.5V and let me know the results.

Respected Sir,

The power supply that I am using is a variable supply of 0 - 30 V and 3 A current rating. The MPPT divider has been adjusted to give the voltage above 1.5V. But that voltage is not appearing across MPPT pin of the IC. There is no problem with IC as I have put new one.

Thanks and Regards...

Respected Sir,

The power supply that I am using is a variable supply of 0 - 30 V and 3 A current rating. The MPPT divider has been adjusted to give the voltage above 1.5V. But that voltage is not appearing across MPPT pin of the IC. There is no problem with IC as I have put new one.

Thanks and Regards...

Please attach an actual schematic of your PCB (not the data sheet application schematic).

The voltage on the MPPT comes from a resistor divder connected to the output of the solar panel and the center point of the divider is connected to the MPPT pin.  As the solar panels is loaded toward it maximum output its output voltage will drop and when near the maximimum output of the solar panel the divider voltage should drop down and approach 1.2V.

Here is the schematic :

Thanks and Regards...

The 499k and 16k mPPT divider you have calculates to 38.6V input at maximum power point.

Typically the open circuit voltage is 120% of the maximum power voltage, which means that your solar panel OC voltage would be 48.3V.

Respected Sir,

The MPPT voltage divider is set with the resistances of 499K and 36K (not 16K). Hence as per the MPPSET formula, the MPPSET voltage would be around 30V (which I think is high as the open circuit voltage of my solar panel is: 21V ). With this regard, what should be the MPPSET divider resistances ?

I did some calculations assuming the MPPSET voltage to be 17.8Vdc. Then from the MPPSET formula, I calculated the divider resistances. I assumed one of the resistances to 100K and found out that the other resistance would come up to approx. 8K. Will these values suffice to my application?

Also, If I look at the application notes which I am referring to, the MPPSET resistance values are same and it says that  " MPPSET voltage is set at 17.8Vdc from the factory." Does that mean that the MPPT divider resistance values are different from those given in the application notes ?

Thanks and Regards, 

Use 464k and 36k

Respected sir,

As per your advice, I replaced the MPPT resistor divider with 464K and 36K and connected solar panel at the input terminal instead of lab power supply. Also connected a 103 Thermistor in between TS and Ground pin.

Now, the TS pin is within the range of its operational window (at 1.8V). Also, the REGN pin is showing the voltage of 6V. But MPPSET pin of BQ24650 shows only 0.5V ( it should be  greater than 1.5V as you mentioned in your previous post) . I tried changing the MPPT resistor divider ratio, but did not observe any significant change. The TERM_EN pin is pulled to VREF. 

What seems to be the problem?

Thanks and Regards, 

The MPPS divider should be biased by the input source.  What is the voltage at the input, where the divider is connected?

Respected Sir,

The input voltage is fed from a solar panel. The voltage is 21V at 2.23A current. 

with the divider values suggested earlier, this will result in 1.51V at teh MPPT pin and the converter should be delivering power.  Is it working?

Sir,

With divider values suggested earlier, the voltage at MPPT pin has dropped down to 0.85V. Earlier it was 1.2V.  

Also I would like to know the why switch is included in the circuitry? 

Thanks and Regards,

Sir,

With divider values suggested earlier, the voltage at MPPT pin has dropped down to 0.85V. Earlier it was 1.2V.  

Also I would like to know the why switch is included in the circuitry? 

Thanks and Regards,

See attachment for MPPT divider information.  MPPT = MPPSET which is pin 2 of the device.

Thank you very much sir. I will test my circuit according to the document.

Regards,

You are welcome.