BQ24650: Battery connected to bq24650 in not charging

Hi Nagaswaroop,

Welcome to the TI E2E forum!

Can you send a schematic for this design? This will help on finding the root cause.

Also, send scope screenshot of VCC, SRN, PH and REGN. What is the DC voltage on VCC, SRN, and REGN?

I want to remind that 10A charging current can generate heat, and suggest that there is enough copper pour under the IC and a GND plane to dissipate heat.

Regards,
Steven

Below are the DSO screenshots of Bq24650's VCC, PH, REGN, VFB, Vmppset and SRN pins:

Figure1: VCC pin voltage of Bq24650

Figure2: PH pin voltage of Bq24650

Figure3: REGN pin voltage of Bq24650

Figure 4: SRN pin voltage of Bq24650

Figure 5: VFB pin voltage of Bq24650

Figure 6: Vmppset pin voltage of Bq24650

Below are the voltage measured by using digital multi-meter on respective pins of Bq24650:

VCC=24.22V

PH=11.56V

SRN=11.56V.

REGN=0V

Vmppset=1.985V

VFB=2.42V

Attached is the schematic of Bq24650 MPPT design

MPPT-12V 10A Li-ion revised 1.pdf

Please help us to resolve this issue ASAP

Regards-

Nagaswaroop

Nagaswaroop,

VFB is higher than the regulation point of 2.1V, meaning that your resistor divider for VFB is not properly configured. If VFB is higher than 2.1V, then it thinks that the battery does not need more charging.

In the schematic I find a few things that need to change:

1. C10 to 22pF

2. R1 to 100k and R2 to 500k or similar (need to verify the correct ratio, as VFB needs to be lower than 2.1V to start charging)

3. I recommend using surface mount FET for less parasitics

4. Remove C8 and C9. Replace with 4x10uF caps. Place all 4 caps after SRN sense resistor.

5. Make sure that in the layout SRP and SRN are in Kelvin connection.

6. Please try to use a single inductor, and its recommended to use 3.3uH.

7. With a sense resistor of 5mohm, your regulation current will be 8A. A sense resistor of 4mohm is needed for 10A charging current.

8. Your MPPSET is set to 18V, which for 17V you would need to adjust the resistor divider, to a ratio closer to 13.17.

8. Use the calculation tool to calculate values if needed.

Follow the picture I attach here for the power stage, it is the optimized way to layout a buck converter. Reduce loop on input and output currents.

Let me know if you have any questions on this.

Regards,

Steven

Hello StevenB,

Thanks for your valuable inputs, we will make the changes accordingly and let you know the results.

We used 33µH having 3A saturation current ,since we need saturation current more than 10A for our design, we connected 4nos of 33µH having 3A saturation current. And below are the few  more queries on current design:

1.Is Vmpp and Vin voltage are same? 

2.I have designed input voltage regulation for Vmppset=18V , battery voltage regulation for 12.6V,theoritical duty cycle obtained for 
   vin=18V and vout=12.6V is 70%, Iripple is 1.909A , Isat>=10.9545.

Below are the practical voltages observed when I connect the digital Multi meter -ve probe at Signal GND(battery GND):

Voltage measured on power supply is 12.50V.

For Vin 12.16V, voltage obtained on Vmppset pin is  0.814V

For Vbat 11.29V,  voltage obtained on Vfb pin is 1.87V 

Voltage on top side MOSFET gate is 11.57V , drain is 12.38V, source is 11.57V

Voltage on bottom side MOSFET gate is 0V , drain is 11.57V, source is 0V.

Below are the practical voltages observed when I connect the digital Multi meter -ve probe at BQ24650 IC pad (main GND):

Voltage measured on power supply is 12.50V.

For Vin 12.38V, voltage obtained on Vmppset pin is  1.040V

For Vbat 11.51V,  voltage obtained on Vfb pin is 2.096V 

Voltage on top side MOSFET gate is 11.57V , drain is 12.38V, source is 11.57V

Voltage on bottom side MOSFET gate is 0V , drain is 11.57V, source is 0V.

I have connected two GNDs through 600ohm bead resistor and used SR3100 diode in place of Q1(P-CHANNEL MOSFET).

By practical  observation we found that voltage on Vfb pin is below 2.1V, even then battery is not drawing current, can we know the reason for this?

Please help us ASAP.

Regards:

Nagaswaroop 

One more update, voltage on Vref pin is 0.404v even after setting VCC= 22V of Bq24650 and we placed bq24650IC on daughter card and rigged up the circuit in bare PCB.

Hi Nagaswaroop,

You may have to fix the TS resistor values in order to get the correct voltage at TS pin. I think I gave you the link for the calculation tool on my first post. Here it is again www.ti.com/.../sluc175 .

It also looks like you are confusing the functionality of MPPSET. MPPSET is used to regulate input voltage, because for a solar panel, the maximum power that can be output is a function of voltage. You want to maintain input voltage at the peak power point of the panel.

If you are using a power supply, the input voltage would have to be at 19V for the charger to operate properly. In the schematic, you designed for 18V MPPSET, which means input voltage would have to be above 18V for it to operate.

Regards,
Steven

Hello Steven,

I have tested by giving 19V for VCC, but battery is not charging, that's why I performed IC test. Today I  shorted two GNDs, gave 19V VCC and checked circuit board but now also battery is not charging.

Is it possible to provide us sample evaluation board for testing?

Regards-

Nagaswaroop

Nagaswaroop,

I just noticed in your schematic has Q1 that is not connected to any other signal. Short out Q1 and try again. For the final schematic, you want to change Q1 to a diode. Try to have 19VIN, 11.1VIN, TS at 2V and short Q1. This should enable your charge.

You can purchase an EVM from our TI website.

Regards,
Steven

MPPT-12V_10A_LI-ION_V1_1.pdfHello Steven,

Has I already mentioned in my previous mail I am using SR3100 diode in place of P-channel MOSFET(Q1) at input.

For your reference I am sending the edited  Schematic which contains the Diode (D1) in place of P-Channel MOSFET (Q1)  

Attached is the Schematic.

And can I know what is need of Q3 MOSFET at MPPSET pin which uses CE signal.

Regards:

Nagaswaroop

Nagaswaroop,

Yes you did mention it before. The Q3 MOSFET at MPPSET is there to enable or disable charge, you can control this with and MCU or any external signal. This FET should be off so that the charger can start, assuming that input voltage is above MPPSET.

Regards,

Steven

Sounds good. Let me know if you have any questions on the layout.

Regards,

Steven

Hello Steven,

Hope you are doing good.

We have designed the new schematic by referring  Bq24650IC EVM Board schematic. Please  let us know if any changes need to be incorporated .

Attached is the schematic of new design.

Regards,

NagaswaroopBq24650IC_EVM_CKT.pdf   

Hi Nagaswaroop,

Good to hear from you again. I have reviewed the schematic and here are a few things:

1. Change C5 to 1uF

2. Calculate TS resistors based on the calculator on the bq24650 page of www.ti.com/.../sluc175

3. R6 resistor value is too high, please calculate how much charge current you want with the formula ICHG = (40mV/RSNS). If charge current is 8A, then sense resistor has to be 5mohm.

4. Use CSD18504Q5A for Q1 and Q2, surface mount MOSFETs have better heat dissipation and less parasitics, which mean better efficiency and smaller board area.

5. Q3 could be changed to a smaller FET as well.

6. You may want to change R24 to a higher value so that variable MPPSET works.

7. C15 should be 22pF

8. Change R00 to a higher value for variable VBAT.

I emphasize the fact that its better to use surface mount devices for DC/DC converters in general because of better heat dissipation and reduced parasitics, which improves the switching waveforms.

For the layout, make sure there is enough copper pour for heat dissipation, keep the switching lines away from sensing lines, and pack the power stage as close as possible, with input caps very close to high side fet, sense resistor very close to the inductor and output caps very close to the sense resistor.

Regards,

Steven

Hello Steven,

 Thanks for your valuable inputs.

We considered your inputs,do the changes accordingly  and let you know the results.

Regards,

Nagaswaroop

Hello Steven,

We have incorporated the changes which you mentioned  in our design and designed the  PCB layout for the same. Attached is the updated schematic and PCB layout design(with gbr and PDF format15a mppt.zip) , please go through and let us know if changes need to be incorporated.

Please do the needful ASAP.

Regards,

Nagaswaroop

Nagaswaroop,

The thermal pad on the FETs have to be connected to drain. Try to route everything related to PH switching node on the same layer (Input cap, high side fet, low side fet, inductor, sense resistor, output cap).

Connect all the legs of the FETs to the traces as well, use copper pour to connect all these lines together. All the drains together and all the source together. Use wide traces as these are power traces and require the width for power, especially for 8A charging.

The C19 cap is not needed, if you want to add a cap here, I recommend lowering it to 0.1uF.

Also, make sure the sense resistor is 5 milli ohm and not 5 ohm.

Regards,
Steven

Hello Steven,

Hope your doing good,

By considering the inputs given by you, we designed the BQ24650EVM board, but now also we are facing problem in charging battery.

Below are the readings and issues we are facing:

Voltage readings w.r.t GND:

VCC=19.7V.

MPPSET=1.89V.

VREF=3.35V.

TERM_EN=3.35V.

SRN=12.64V.

SRP=10.32V.

REGN=6.11V.

LODRV=2.88V.

HIDRV=8.62V.

PH=5.5V to 6.5V (Varying)

BTST=5.5V to 8.8V (Varying)

Ibat (while charging)=5.91mA.

Vbat (while charging)=12.65V.

Vbat (while not charging)=12.65V.

Issue:

From the above voltage reading except  Vbat (while charging) and Vbat (while not charging) it clear that criteria for charging is met but charging current by battery is in order of mile amps only not in amps. For further details I have attached  containing  the DSO images .

Please help us to resolve this issue ASAP.

Regards,

Nagaswaroop

1.BTST

2.HIDRV

3.LODRV

4.PH

5.SRP1

6.SRP2

Bq24650EVM Related Videos

Nagaswaroop,

Please check your sense resistor(R6) is 5mOhm or not. and measure the voltage between SRN and SRP(on C14 as well).

Alen Chen

Dear Alen Chen,

Thank you for your valuable inputs.

 I checked the circuit, yes it was the issue with current sense resister, I was connected 5ohm instead of 5miliohm. Now I am testing with 1miliohm current sense resister, battery is charging in Amps now.

NOTE: Due to  non-availability  of 5miliohm resister I have used 1miliohm  resister for testing purpose only.

Regards,

Nagaswaroop 

Dear  Alen Chen,

Please let us the Test cases,effect of PWM frequency,effect of duty-cycle of High side gate driver and low side driver, effect of voltage on Vmpptset and Vfb pins on charging, to ensure the proper operation bq24650IC.

Please do the needful ASAP.

Regards,

Nagaswaroop

Dear  Alen chen,

Also please let us know what is the efficiency we can achieve using Bq24650

Regards,

Nagaswaroop

Dear Alen  Chen,

Please explain us that how the Bq24650 maintenance out battery voltage and current constant by increasing or decreasing input PV voltage or current I.e if you we increase PV voltage PV current is decreases or if you we decreas PV voltage PV current increases ,which leads to achieve constant system efficiency. Can you please explain how it is happening.

Please do the needful.

Regards,

Nagaswaroop

Dear Alen Chen,

Sorry for the mistakes in my last post.

Please explain us the bq24650IC internal MPPT operation for different battery charging profile and also explain how it is enabling system to achieve constant efficiency irrespective of input(voltage or current) variation.

Regards,

Nagaswaroop.

Dear Alen Chen,

We are testing bq24650 Operation for lifePo4 battery 12.8v(3.2v cell) 15Ah.

Below is the procedure we followed:

1.Setted output voltage without connecting battery to 14V, by varying the pot connected between Vfb pin and battery output. Vfb pin voltage read on multimeter was 2.09v.

2.After connecting battery for charging,battery output voltage read on multimeter was 13.34V and voltage on Vfb pin was 1.98V.

LifePo4 battery before connecting for charging was 13.30V.

From datasheet for fast charging voltage on Vfb pin should be between 1.55V to 2.1V. In our case it was 1.98V I.e its within the fast charging voltage range only even then battery was not charging.

We tried the same procedure for li-ion 11.1V battery(3.7V cell ), setting output voltage without battery connected, to 12.8V (Vfb pin was 2.09V) .

After connecting battery output was 11.5v(Vfb pin was 2.089V)it was working fine, but same procedure is not working for lifePo4 battery, please let us know if any changes need to done in circuit.

Please do the needful.

Regards,

Nagaswaroop.

Hi Nagaswaroop,

Please try to discharge you Lifepo4 battery to 12V then try again. If still won't works, please measure all of Pins' voltage.

Alen Chen

Hi Alen,

We are checking the charging profile with Lifepo4 battery. we made changes as per the EVM  schematic for lifepo4 in voltage divider (R13,R15,R22) w.r.t calculations in the attachment.

Could you please help us in calculating right resistors values. From  Application note we calculated the charging voltage for two cases as mentioned below.ie

1) When R22||R15 (Q3 On), the charging voltage range is from 14.26V to 14.61V

2) when R22 is not in parallel with R15 (Q3 Off), the charging voltage range is from 12.54V to 12.85V

When  we connect battery voltage of range from 12.85V to14.26V battery will not charge .

We want BQ24650 to charge the battery from 12.6V to 14.6V window,Please let us know the design changes need to be incorporated.

Attached is the voltage divider calculations for Charge and recharge voltages as per application report of bq24650 to Charge LiFePO4 Battery   

slua565.pdf

Please do the needful ASAP.

Regards,

Nagaswaroop

Dear Alen Chen,

We also tried for,

Vrefrecharge=8.2v (2.05v*4cell)

Vrefcharge=8.4v (2.1v*4cell)

But result remains same.

Regards,

NAGASWAROOP

Hi Alen Chen,

Attached is the datasheet of 12.8V 15Ah lifePo4  battery. Guide us to design the circuit for the same.

Below is the detailed explanation of the issue:

From application report Vrecharge measured at Vfb pin is regulated to 2.05V and Vcharge measured at Vfb pin  is regulated to 2.1V, we understood the below mentioned points from application note.

1) If the battery voltage on Vfb pin drops below 2.05V (recharge threshold) the battery will not charge.

2)As soon as the battery voltage on Vfb pin  becomes  more than 2.05V battery will start charging because its above recharge threshold and stops charging if it exceeds 2.1V.

In case if there are any other factors need to be considered other than the above mentioned, please update us.

In our case as soon as we connect  the battery for charging, the voltage on Vfb pin  is drops below 2.05V and  battery is not charging (Refer figure1 and 2). Battery voltage before connecting for charging was 13.30V(when not charging).

But when we connect the battery of 12.7V (when not charging) for charging , the voltage on Vfb is above 2.05V   and battery will keep on charging (Refer  figure ) till 12.85V and stops.

Now we need to design the circuit for recharge threshold  of 11.2V and charge threshold  of 14.6V, that means when we connect battery voltage between 11.2V to 14.6V, the battery should start charging constantly till 14.6V.

Above voltage readings are w.r.t the calculation attached.

Fi

Figure 1:When the voltage on Vfb pin drops below 2.05V and  battery is not charging.

Figure 2:Scaled up version of figure 1 .

Figure 3:When the voltage on Vfb is above 2.05V   and battery draws continuous charge

LiFePo4 Module_12.8V-15Ah (6).pdf 

Note :In figure 1, 2 and 3 Scope images the channel 1 shows HIDRV pulses and  channel 2 shows LODRIV Pulses.

Kindly do the needful. Awaiting for your valuable response.

Regards,

Nagaswaroop

Dear Alen Chan,

Kindly assist on the  mention issue  ASAP , we are awaiting for your valuable response .

Please do the needful.

Regards,

Nagaswaroop

Dear Alen,

We are developing 12/24V MPPT charger  using Bq24650, for 24V PV system Voc is 40V but  Bq24650 Vcc pin maximum voltage tolerance is 33V and pins like STAT1, STAT2, SRP, SRN and PH are also have maximum voltage tolerance less than 36V, what are changes need to incorporated in our design for 24V system.

Regards,

Nagaswaroop,

R & D Engineer

Renewable Energy Applications & Products – ReAP

Dear Ann Lien,

The we are developing the 12V/24V  15A MPPT LifePo4 battery charger. Currently we are evaluating the 12V system.     

Our end product system specification as follows:

Battery Type used: 12.8V 15Ah LIfePo4.

Auto Sensing:12V/24V battery and PV.

Help needed from IT support team  on 12V / 24V 15A MPPT charger design:

1.What are changes need to be incorporated  in our current design.

2.What are the protection need to  be incorporated  in our current design.

Attached is the schematic of our current design.

Note:

In schematic below are components which are not installed:

R4,R16,C19,C9,R8.

In schematic below are the changes did after PCB design:

1.JP8 and JP5 are open and are directly connected to Vin.

2.Replaced 5E with 5mE(0.01E || 0.01E).

 bq24650_ckt_v1_0 (Restored).pdf

Regards,

Nagaswaroop

Dear Ann Lien,

Kindly reply, we are awaiting for your valuable response.

Regards,

Nagaswaroop