LMQ66420: LMQ66420R5 part failure

Hi,

Any external boot capacitor must be connected between the switch and boot pins. Can you please confirm if this was connected or not?

Additionally, do you have any scope shots to share what the failure was? What was observed to have failed?

Thank you,

Joshua Austria

Hello Joshua,

From the datasheet  it was mentioned there is internal capacitor connected between BOOT & SW pin.You still recommending to add external capacitor?
Additonally we observed IC short during power ON what kind of scope shots you are expecting?

Hi, 

Sorry, I am unclear as to what that scope shot is of?

The boot capacitor is not necessary, but if one were to be connected, it should not be between Boot and FB, but instead between boot and SW. I was asking to confirm if this capacitor (C64) was DNPed or not. 

Can you please also share what connections if any are connected to this schematic? What additional circuitry was connected on the 24 V and 3V3 rails when the device failed?

Thank you,

Joshua Austria

1) This is 12V input  Voltage capture for LMQ66420. Yes C64 is currently DNP

Hi,

Understood. Can you share what the output voltage and SW waveforms are along with this VIN ramp? It is not clear to me yet what the failure is on the device at the moment. 

Do you also have any additional details to share about what connections are connected to the schematic on input or output? 

And sorry another confirmation, was C64 populated when the device was damaged?

Thank you,

Joshua Austria

Hello Joshua,

C64 not yet mounted.

Pls find the Load details for  3.3V 
Also attached 
1) 12V VIN Vs 3.3V VOUT
2) 12V VIN Vs  SW Node

Hi,

It seems that the device is properly outputting 3.3 V with 12 VIN. What seems to be the issue that you are seeing with this device operation? Where is the IC short that is being observed?

Thank you,

Joshua Austria

Helllo Joshua,

The attached scope  image is taken from  another working IC . Actual failure part have low impedance those measurements were update in earlier conversation .

We have observed low impedance/failure in one of the 12V to 3.3V LMQ66420 buck converter  ,let me know any further details if you need.

Hi Saravanan, 

I have a couple of additional questions:

• Do you have impedance measurements for your application with a working IC? If so please provide these.
• Additionally, is this failure repeatable?
• What load was being drawn from the device at the time of failure?
• Is the VIN ramp provided by the working IC the one that was provided to the failing IC's?
• I will also need the connections on the input and output shared as well to help us better diagnose this. Please also provide the inductor current and capacitor voltage ratings.

Thank you,

Joshua Austria

Hello Joushua,

• Do you have impedance measurements for your application with a working IC? If so please provide these

            Will update you

• Additionally, is this failure repeatable?

            Yes ,we have observed in 3 boards.

• What load was being drawn from the device at the time of failure?

            Could you share your Mail Id .So that i can send the actual schematic with you.

• Is the VIN ramp provided by the working IC the one that was provided to the failing IC's?

            Yes.

• I will also need the connections on the input and output shared as well to help us better diagnose this. Please also provide the inductor current and capacitor voltage ratings.

            Inductor : VLS6045EX-1R5N TDK Corporation | Inductors, Coils, Chokes | DigiKey

           Capacitor : 0603YD226MAT2A KYOCERA AVX | Capacitors | DigiKey

Regards,

K.Saravanan

Hi Saravanan,

I sent you a request to connect on E2E. You can send the schematic through the message function.

Thank you,

Joshua Austria