Ringing on MOSFET GATE - Design Review Request

Tobias Franz

Part Number: BQ24650

Tool/software:

I am currently developing a 60W solar charger and facing issues with the dcdc converter stability.

In my first design I could draw 60W with a power supply and an electronic load. When I connected the PV-Cells the charger never started and I only could hear clicking noises from the inductor.

I reworked different aspects of my layout according to the datasheet recommendations but With the new design I am currently facing more issues than bevor.

With no load the BQ24650 tries to regulate the output voltage but can not stabilise it permanently. When I activate the load the voltage is stable but only draws 2 Watts.

The ringing on the mosfet gates does not look good as well. I encountert this also in my first design especially with little loads.

Vref = 3,3V

REGN = 6V

STAT1 indicates charging

MPPSET = 2,4V which is weird. Uin Power Supply = 21V Resistors are set for VMPP17,6V

Due to my heatsink solution for the mosfets the power stage is desinged on the top layer and the controller is routed on the bottom layer.

Could you please give me recommendations on the schematics and the layout to improve my design?

11 months ago

0 Christian Moyer 11 months ago

TI__Mastermind 32016 points

Hello tobias,

I'm reviewing your schematic and will provide feedback after I gather more information.

Best Regards,

Christian

0 Christian Moyer 11 months ago in reply to Christian Moyer

TI__Mastermind 32016 points

Hello Tobias,

I have a few questions?

Where are you applying the system load?

You stated the MPPSET is 2.4V, Can you confirm the input voltage is 21V and R1=200k+100K, and R2=22K.

I'm assuming this is without a battery connected? Do you see any difference with battery connected.

Best Regards,

Christian.

0 Tobias Franz 11 months ago in reply to Christian Moyer

Prodigy 40 points

Hello Christian,

thank you for your reply.

The system load was applied at the battery terminal. This was performed according to the function test described in the BQ24650evm manual.

I just checked again and can confirm that the MPPSET is still at 2,4V with and without the battery connected. The resistors values are as mentioned. I even replaced the BQ24650 to be sure.

Please see the MPPSET voltage below. Looks also very noisy and unstable.

Best regards

Tobi

0 Christian Moyer 11 months ago in reply to Tobias Franz

TI__Mastermind 32016 points

Hello Tobias,

Thank you for the scope capture, I'm reviewing the information and will provide feedback after I gather more information.

Best Regards,

Christian.

0 Christian Moyer 11 months ago in reply to Christian Moyer

TI__Mastermind 32016 points

Hello Tobias,

Do you see any difference if you apply an actual batteryor sourcemeter to the battery terminal?

Best Regards,

Christian

0 Tobias Franz 11 months ago in reply to Christian Moyer

Prodigy 40 points

Hello Christian,

when I connect the battery the behaviour is the same.

The controllers indicates charging but the input power is only about 2W.

The MPPSET Voltage also stays at 2,4V.

Best Regards,

Tobi

0 Christian Moyer 11 months ago in reply to Tobias Franz

TI__Mastermind 32016 points

Hello Tobias,

I don't understand how that is possible. If the Input is 21V and R1=200k+100K, and R2=22K, then the output should be 1.4V on MPPSET. Is MPPSEt shorted to another pin? Do you still get the same output if you remove the connection between Vout of the resistor divider and MPPSET pin?

Best Regards,

Christian

0 Tobias Franz 11 months ago in reply to Christian Moyer

Prodigy 40 points

Hello Christian,

I checked all the connections again and found that the connected button (Restart for Charger) was damaged.

I now have 1,2V MPPSET ~ 17,6V input. But the signal is still noisy and the charging power remains at 2W.

Best Regards,

Tobi

0 Christian Moyer 11 months ago in reply to Tobias Franz

TI__Mastermind 32016 points

Hello,

We have limited bandwidth this week, I will provide feedback by EOD Monday.

Best Regards,

Christian

0 Christian Moyer 11 months ago in reply to Christian Moyer

TI__Mastermind 32016 points

Hello Tobias,

What is the value of R143 and R3

Best Regards,

Christian

0 Tobias Franz 11 months ago in reply to Christian Moyer

Prodigy 40 points

Hi Christian,

the combined resistance is 8mOhm and each resistor has 16mOhm.

I wanted to have an option to reduce the charging current by removing one sense resistor.

Best Regards,

Tobias

0 Christian Moyer 11 months ago in reply to Tobias Franz

TI__Mastermind 32016 points

Hello Tobias,

What size inductor are you using?

Can you provide a scope capture of the input current/volatge and load current/voltage?

Tobias Franz said:
The controllers indicates charging but the input power is only about 2W.

Is the input power limited to 2W or the output power? Have you tried using a different input supply?

Best Regards,

Christian

0 Tobias Franz 11 months ago in reply to Christian Moyer

Prodigy 40 points

Hi Christian,

please see the measurements below:

I used a 0,33Ohm resistor for the current measurement [Differential Probe: TESTEC TT-SI9110]

Uin - Usolar

Iin - Isolar

Uout - Ubat

Iout - Ibat

I am currently using a 6,8µH inductor (WE 74439369068).

The current limit of the source is set to 8A so this shouldn´t be a problem.

The previous version of the pcb charged with 60W on the same supply, but had the charging issues with the solar panel.

Best Regards,

Tobias

0 Christian Moyer 11 months ago in reply to Tobias Franz

TI__Mastermind 32016 points

Hello Tobias,

What did you chang between these two boards, the one that can draw 60W, and the one that can only draw 2W.

Can you provide your PCB layout file?

Best Regards,

Christian

0 Tobias Franz 11 months ago in reply to Christian Moyer

Prodigy 40 points

Hi Christian,

I separated the PWRGND from the AGND and added Gate resistors for testing.

I also did some Layout changes.

How can I provide you the .fbrd file (Fusion 360). I can´t drag it in here.

Do you see any major issues with my schematic? I can redo the layout which is no problem.

Best Regards,

Tobias

0 Christian Moyer 11 months ago in reply to Tobias Franz

TI__Mastermind 32016 points

Hello Tobias,

You should be able to put it in a .zip file and drop the .zip file in the thread. Or you can send it to my email c-moyer@ti.com

Best Regards,

Christian.

0 Tobias Franz 11 months ago in reply to Christian Moyer

Prodigy 40 points

Solar Charger prev design.zip

0 Christian Moyer 11 months ago in reply to Tobias Franz

TI__Mastermind 32016 points

Hello Tobias,

I'm reviewing this information and will provide feedback by EOD Monday.

Best Regards,

Christian.

0 Christian Moyer 11 months ago in reply to Christian Moyer

TI__Mastermind 32016 points

Hello Tobias,

I don't see ay obvious issues with your PCB layout.

If you add in the resistor and capacitors on the input do you see the thee MPPSET voltage stabilize?Ss

What is the load current set to?

If you apply a load of 2A at either of these nodes, are you able to support the load?

Best Regards,

Christian

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Ringing on MOSFET GATE - Design Review Request