Issue link: https://iconnect007.uberflip.com/i/726276
September 2016 • The PCB Design Magazine 43 nal 47uF value. Considering the 20% initial tol- erance rating on the part, plus the additional few percent for DC bias effect and the expected 20-30% capacitance drop due to AC bias effects [4] , the 38uF is way within the expected range. Many capacitors from major component manufacturers also have various models avail- able, from which we can get the typical ESR val- ues. In case this data is not available and we may suspect that the ESR value we got from curve fit- ting might be wrong, we can continue the test- ing and collect more data. If we want to check the parameters of the same exact capacitor that we have on the evaluation board, we can for in- stance measure the output impedance with the converter turned OFF, so that across the out- EVALUATING EVALUATION BOARDS Figure 4b: Bill of materials of the LM20143 evaluation board used in reference 3. Figure 5: Correlation of measured output impedance to a three-capacitor model at 4.5V input voltage, 1.2V output voltage and 1A DC load current.