How Does Power Reach the Earbud Through the Charging Contacts?
Follow the circuit through one earbud. The case's power-management circuit supplies voltage to the positive pin in the well. That pin touches the corresponding earbud pad, which connects to the input of the earbud's battery charger. Current returns through the earbud's ground pad and the second case pin. A poor connection on either side can reduce the voltage available to the charger.
The external charging interface serves a different part of the circuit. A case can receive power through USB or a wireless charging coil and still use metal pins to deliver power to the earbuds inside.
Two contacts can also support more than charging. The published MAX20340 earbud application circuit uses a power-line communication contact and a ground return. The case and earbud electronics exchange data over the same pair that carries power. If another design has a third pad, its function should be taken from that model's pinout before assigning it to detection or communication.
How Do the Charging Well, Magnets, and Pogo Pins Work Together?
The molded well determines how the earbud sits. Its locating surfaces guide the shell into position and set the final angle of the charging pads. A silicone ear tip that catches on the wall can lift or rotate the earbud just enough for one pin to land near a pad edge. Check both wells with every ear-tip size supplied with the product. A mark near the edge of one pad can reveal a seating problem that is difficult to see from above.
The pins accommodate variation along their axes. At the largest gap between the pin mounting surface and the earbud pad, check that the shortest installed pin still develops enough contact force. At the smallest gap, check that the tallest pin stays within its permitted working travel and that the combined spring force allows the earbud to sit against the well's locating surfaces.
Where magnets hold the earbud in place, test how it settles with the lid open, then close the lid and repeat the electrical check. If charging starts only after closure, establish whether the case electronics are designed to enable charging in that state. If they already supply power with the lid open, check whether lid pressure is compensating for a high seat or insufficient pin compression.
Which Pogo Pin Specifications Matter in an Earbud Charging Case?
| Specification | What to check in the assembled case |
|---|---|
| Tip profile, tip diameter, and pad size | At the largest permitted earbud rotation, does each tip still land inside the usable metal area? |
| Free height, working travel, and contact force | Measure from the installed pin base to the mating pad. Check each pin at the widest gap and the combined force at the tightest gap. |
| Contact resistance and current rating | At the earbud's actual charging current, measure voltage drop across both the supply and return contacts. Compare the resulting earbud input voltage with the charger's requirement. |
| Pin plating and pad finish | Inspect both surfaces after repeated docking, exposure to sweat residue, and the specified cleaning procedure. Record wear alongside resistance measurements. |
| Mounting method and position tolerance | Measure installed tip height and position relative to the well's locating surfaces. Include PCB seating and housing tolerances. |
A component drawing shows why the force value needs a measurement position. The CPG-16-SMT-B datasheet specifies 25–55 gram-force per pin at a working height of 2.50 mm. Two such pins at that height would exert a combined 50–110 gram-force if their axes are parallel. That calculation gives a designer a starting point for checking retention. The force in a particular earbud case depends on the installed height of each pin and the angle at which it pushes against the earbud.
Why Does One Earbud Charge Only When Pressed Down?
Establish which side carries the fault. Record the affected side, case charge level, lid position, and whether the earbud battery is ready to accept a charge. Where compatible samples are available, try a known-good same-side earbud in the suspect case, then try the suspect earbud in a known-good case. Keep the ear-tip size and charging state comparable.
Compare natural seating with light pressure. On an instrumented sample, record voltage at the earbud charger input and the current delivered to that earbud. Repeat while applying light pressure without changing the lid state. Measuring the case's USB input current alone cannot isolate what reaches one earbud.
Match the correction to the observation. If changing the ear tip restores normal seating, inspect clearance around the tip and shell. If a plunger stays below its original free height after release, inspect it for contamination or binding. If pressure moves the contact mark from the pad edge toward its center, check alignment. When input voltage remains within specification during the fault, check charger enable, battery temperature, and battery state.
How Can Engineers Validate an Earbud Charging Contact Design?
Start with ordinary first placement. Drop each earbud into its own well without pressing or repositioning it. Count a successful placement when charging begins within the product's specified detection time and continues for the defined observation period. Report successes and total placements separately for left and right. Keep attempts that required reseating visible in the results.
Repeat the check at the limiting assembly gaps and after the specified docking cycles. On the same samples, record loaded voltage drop, charging interruptions, plunger return, and wear on both pads. Test clean parts first, then repeat after a defined exposure to representative residue and after cleaning. This sequence can show whether a failure follows contamination, wear, or a shift in how the earbud seats.
For a custom contact review, Dongguan Xinteng Electronics Co., Ltd. can work from the earbud pad drawing, the charging-well locating surfaces, and the minimum and maximum installed gaps. A centered contact mark with too little force points toward working height or spring selection. A mark that moves outside the pad as the earbud rotates points toward pad position or well geometry. Retesting the revised samples under the original conditions shows whether the change addresses the observed fault.
Technical References
MAX20340 Bidirectional DC Powerline Communication Management IC. Datasheet, "Wireless Earbud Charging with Cradle," typical application circuit.
CPG-16-SMT-B Pogo Pin Datasheet. Revision 1.0, November 4, 2024. Working height, contact force, stroke, and mechanical drawing.
