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Hi Team,
My customer designed in LM5176 and found few parts got damaged during tried run phase. Below is SCH.
Test condition is Vin=48V, Vout=50V, Iout=1.5A(by electronic load). Please help to check the SCH is there any improper design.
The pins in red frame of damaged unit have different impedance compare to good unit.
Customer probed some waveforms and please let us know what signals you would like to check or any experiments need to do for the investigation.
Thanks very much.
Vincent Chen
Hello Vincent,
The overcurrent protection is set extremely high, I wonder if the customer is doing output short tests which could lead to a saturating inductor.
For me it is difficult to understand the measurements in the Excel file. Please check especially the BOOT1 and BOOT2 voltage with respect to the switch nodes.
Hi Brigitte,
Please find the boot1/2 and SW1/2 waveforms under different conditions.
Thanks a lot.
Vincent
Hello Vincent,
The measurements show -18V on the gate drive signals. Please add gate drive resistors, up to 5 ohm to check if the devices survive then.
In addition, there is a lot noise on the switch node measurements. How many layers is the design using?
Hi Brigitte,
Regarding SCH portion, customer populated wrong capacitor in the compensation circuit. The original design the value of C26 should be 47nF, but it was populated by 47uF wrongly. Customer used the calculation sheet to run the bold plots for two conditions as following.
Could you advise which one is the proper value?
C26= 47uF
C26= 47nF
Btw, the PCB is 4 layers.
Thanks a lot.
Vincent Chen
Hello Vincent,
47uF is for sure the wrong value for the compensation. This makes load responses very slow and it could happen that the overshoots happening on the output cause damage to the system.
The quick calculator is calculating the necessary values for the compensation network. The customer only needs to make sure that he selects a crossover frequency that is low compared to the right have plane zero.
Hi Brigitte,
Customer's design spec. is as following,
Vin : 10~50V
Vout : 50V
Iload : 1.5A
Could you please comment the values of compensation circuit below is OK or not(C26=47nF)? Or, do you have suggested values for this application?
Thanks very much.
Vincent Chen
Hello Vincent,
Please use the Quick Start Calculator on the LM5176 product folder to check if these values are ok. Please add the calculator result here if it is showing issues with the components used, then we can dig more into the details.