Inductive Crosstalk Study of Embedded Current Sensor for SiC Die Current Measurement

Measuring the individual die currents in a multichip power module can aid in layout optimization, die selection and testing of current balancing strategies during the design phase. Thus, a two-stage current sensor concept with an embedded current transformer has been proposed. However, the magnetic crosstalk between the sensors and the layout and how it impacts the current sharing measurements has not been investigated. The embedded current transformers are in close proximity to the cobber traces in the layout yielding parasitic magnetic couplings between each transformer and these traces. During switching the parasitic magnetic couplings are triggered yielding an extra contribution to the die current measurements, which impacts the accuracy of the current sensors. Ansys Maxwell is used to determine the strength of the different parasitic magnetic couplings between the current transformers and the nearby cobber traces in the layout and a return wire is introduced for each transformer to mitigate the induced crosstalk. The return wire mitigation strategy is demonstrated and for the most crosstalk prone current transformer, a reduction in induced crosstalk from 7.3 to 2.8 % of the switched die current is achieved.