KIT-CRD-CIL12N-BM

Raghuselva

In the dynamic Characterization Evaluation Tool Optimized for the 62mm (BM) Module Platform I am seeing two capacitors are used such as bulk and high frequency with value of 0.1 micro farad 30 nos and 200 micro farad as single bulk capacitor. I need to know the reason of adding high frequency capacitors in that circuit.

ChrisN

Hello Raghuselva,

Thank you for your question. The high-frequency capacitors are employed to reduce the power loop inductance of the evaluation board. By placing several of the high-frequency capacitors in parallel, such is the case with the 62 mm evaluation board, the parasitic inductance of the power loop is reduced compared to simply employing the bulk capacitance by itself. This lower inductance can reduce the drain-to-source overshoot voltage. Importantly for evaluation measurements, the reduced inductance enables more accurate measurements of the device under test (DUT) since the measurements are less influenced by the circuit board parasitics. Notably, the capacitor size between the bulk capacitors and the high-frequency capacitors were specifically selected to differ by several orders of magnitude to limit the influence of the resonances on the parallel capacitors.

Thanks,

Chris N.

Raghuselva

Thanks chris. I need some inputs from your side too conduct double pulse test of CAS120M12BM2 module I selected DC film capacitor of 15 microfarad KEMAT make C4AQILW5150A36J 10 nos in parallel connection. In that case also is it I need to add high frequency capacitors. Please give your suggestions

ChrisN

Hello Raghuselva,

Thank you for your follow-up question. One of the most important aspects of a double-pulse test (DPT) is a high-quality printed circuit board (PCB) layout or equivalent bussing structure. With a bad PCB layout, the measurements will be poor regardless of your capacitor(s) selection. Techniques such as flux cancellation should be employed in order to reduce the PCB inductance. More information about DPT best practices can be found here. If possible, our recommendation is to use the KIT-CRD-CIL12N-BM evaluation kit for performing DPT measurements on 62mm power modules since that evaluation kit has been extensively characterized and is known to be reliable for evaluating 62mm power modules.

Please recognize that the capacitors you selected are limited to a voltage rating of 800V. This voltage rating should be observed when performing DPT experiments. Otherwise, there is generally no universal guidelines for employing high-frequency capacitors. We typically use high-frequency capacitors in our DPT evaluation boards, since the high-frequency capacitors integrate well into the overall PCB layout. Specifically, our designs adhere to the following two non-inclusive principles.

1. The high-frequency capacitors do not introduce additional inductance into the power loop. If for instance, you have to significantly adjust your bulk capacitor routing in order to add the high-frequency capacitors, then I would recommend avoiding the high-frequency capacitors. There is no benefit to adding the high-frequency capacitors if they will significantly degrade the inductance of the overall power loop. 
2. The high-frequency capacitors should have a small loop area to the power module under consideration. If for instance, the high-frequency capacitors were placed geometrically far from the module, then the impact of the high-frequency capacitors is negligible and they should be avoided. For the high-frequency capacitors to be impactful, they must have a short loop area to the power module. 

Without knowing the full details of your application, I would include the high-frequency capacitors, but you should consider the points mentioned previously when evaluating whether they are right for your application. Also, I would again recommend reviewing the Dynamic Characterization and Measurement Methods knowledge article before proceeding with a custom DPT setup.

Thanks,

Chris N.

Raghuselva

Thanks chris, the said board is not available in market that's why I plan to test with own developing board

TBhatia

Hi, I hope that this answered your question. I will close this discussion for now but if you have a follow up question, please "Start a New Discussion" and we would be glad to support you further.