Vcore DrMOS Optimized PCB ACR Loss Analysis And Simulation

- Oct 17, 2018-

PCB main loop ACR model, simulation and measurement

The main power loss components of synchronous buck converter can be summarized as active component loss (MOSFET dc and switching losses, MOSFET driver losses) passive component loss (inductor dc resistance [DCR], ACR and core loss, capacitors equivalent series resistance [ESR]] loss) and PCB loss (PCB, DCR and ACR loss).

Frequency-related PCB losses are caused by the sawtooth ripple current, which circulates in the main loop of the converter given by equation (1) :

Where R ac is the frequency - dependent PCB effective resistance of ripple current waveform.Vcore DrMOS synchronous buck converter with relatively large ripple current at peak efficiency provides a case study.To estimate the loss component of PCB ACR, the single-phase portion of the multiphase Vcore PCB power level layout was imported into Anysys Q3D (figure 1a).The ac current distribution in the ripple current circulation path of PCB main loop is simulated by Q3D, as shown in figure 1b

Total converter loss model and measured values

The total switching loss measurement is carried out on the single-phase Vcore DrMOS evaluation board. With the recommended 150nH inductor, the peak peak ripple current (Ipp) ~ 14.5a is 700kHz under the typical working conditions of Vin = 12V and Vout = 1.8v.The power loss of the converter under the load of 15A was analyzed in the frequency range of 400kHz to 2.5mhz, of which the loss component was extracted in 700kHz (figs. 3 and 4).

The MOSFET loss is estimated by the combination of device measurement and simulation.The ACR loss of inductor winding is based on Q3D simulation, while the core loss and DCR loss of inductor are estimated according to the supplier's data table.The output polymer tantalum solid capacitor (POSCAP) was used to extract ESR losses based on the difference of measured power loss, and the POSCAP was replaced by ceramic.PCB ACR loss comes from Q3D frequency correlation analysis.PCB ACR loss accounts for about 25% of the ripple current resistance loss and about 5% of the total loss at peak efficiency operating frequency of 700 kHz..

The loss component is 700 kHz

The total power loss can be expressed by formula 3: