Distinguishing Input DPM From a Battery Charging Fault

A charger may deliver less than the programmed battery current because the input source cannot support the combined system and charging demand. Input dynamic power management can intentionally reduce charging to keep the source within a voltage or current boundary. Check active regulation states before diagnosing a defective charger.

List the independent limits

Record input current limit, input voltage regulation threshold, battery charge current, thermal regulation, and system power path settings. The TI BQ25628 and BQ25629 data sheet describes input current and input voltage dynamic power management alongside system power path operation.

These limits solve different problems. An input current limit bounds source draw; an input voltage loop can respond when the source or cable droops. Neither should be assumed to equal the programmed battery charging current.

Make a power budget

Estimate input power available at the charger pins after cable and connector loss. Subtract the system demand and account for conversion losses before estimating power left for charging. For a hypothetical 5 V, 1 A source, the ideal input power is 5 W before those losses and loads.

A battery at a lower voltage can have a charging current numerically different from input current in a switching charger. Compare power and the actual conversion behavior rather than expecting the two current readings to match.

Observe the active loop

Measure input voltage at the IC, input current, system current or power, battery current, and relevant status registers. Increase the system load in controlled steps within the supported operating range. Check whether charging decreases when an input limit becomes active.

Repeat with the intended cable and source. A laboratory supply connected through short heavy leads can conceal the voltage drop that causes DPM in the product. Conversely, a bench supply’s own current limiting dynamics can create a different response from the intended adapter.

Review transitions and software behavior

Verify startup, source attachment, source removal, and changes in negotiated or configured source capability where applicable. Ensure firmware does not continually overwrite a limit with an unsupported value or misreport a deliberate charging reduction as a battery failure.

Save source identity, cable, settings, measurements, and active status for each condition. If the required charge time cannot be achieved while the system is active, revise the power budget or operating policy within approved battery and source limits. A successful diagnosis explains which loop limits charging and why; it does not merely increase a current setting until a nominal bench test appears faster.