Checking Current Sharing in a Multiphase Buck Converter

A multiphase converter can regulate its output correctly while one phase carries more current than another. Output voltage alone does not demonstrate balanced power stage stress. Review the current sharing mechanism, sense paths, and thermal conditions before accepting a high current design.

Identify how phase current is estimated

Determine whether the controller uses shunt resistors, inductor DCR, integrated power stage telemetry, or another sensing method. Identify the sharing loop and the points where individual phase information enters it. The Analog Devices discussion of LTC3861 multiphase sharing describes both resistor and DCR sensing and a dedicated current share mechanism.

Use the selected controller’s documented implementation to guide the review. A multiphase label alone does not specify sharing accuracy, phase shedding behavior, or transient balance.

Estimate the significance of sense error

Compare expected sense voltage with amplifier offset, resistor tolerance, and routing induced error. As a simple illustration, a 1 mV error across a 0.5 milliohm effective sensing resistance corresponds to 2 A. This is a scale calculation, not a prediction of a particular controller’s sharing performance.

For DCR sensing, review the matching network and temperature behavior specified by the controller design. The inductor’s electrical and thermal state affects the interpretation of its sensed voltage. Do not replace an inductor solely on nominal inductance without checking the sensing implications. Include tolerance and the physical location of any temperature compensation component in that comparison.

Measure all active phases

Compare phase currents at several total loads and after reaching thermal equilibrium. Record which phases are enabled. A phase shedding mode can intentionally produce an unequal set of active currents, so verify the control state before declaring imbalance.

Use measurement methods with known offset and bandwidth, and avoid changing one phase’s current path significantly to accommodate a probe. Capture transient sharing as well as steady averages when fast load steps matter. A balanced final current does not prove equal peak stress during the transition.

Interpret temperature as supporting evidence

Different component temperatures may result from current imbalance, airflow, copper area, neighboring heat, or component loss variation. Compare electrical current measurements with thermal observations rather than inferring current directly from surface temperature.

Save phase configuration, measured currents, total load, input voltage, sense component details, and thermal conditions. Investigate repeatable imbalance against the available component and controller limits. The release decision should establish acceptable stress for every phase, including relevant operating transitions, instead of relying on a single aggregate efficiency or output regulation result.