Requests for a custom receiver often begin with one line: “We need a 15W wireless charging RX board.” That is enough to open a conversation, but not enough to design a reliable product. The receiver must fit the enclosure, couple with the intended transmitter, supply the real load, manage heat and communicate correctly with the host or battery-charging circuit.
A good custom wireless charging receiver module specification describes the complete use case. It gives the factory enough information to select a coil and electrical architecture, then creates measurable acceptance criteria for samples and production.
Start with the load, not the marketing wattage
Define what the receiver output powers. Is it connected directly to a system rail, a battery charger IC, a power-path controller or a removable battery pack? Each load behaves differently during startup and negotiation.
The specification should include:
- Required output voltage and tolerance
- Continuous current and short-duration peak current
- Load-step profile and acceptable voltage dip
- Startup current or inrush behavior
- Minimum useful power before the host should enable
- Shutdown and restart requirements
- Battery chemistry, cell count and charger interface if applicable
Nominal power is only voltage multiplied by current under one condition. It does not describe how the load changes or how the product should respond when coupling becomes weaker. We prefer a load profile with typical, peak and sleep states.
Define the transmitter environment
An RX module cannot be engineered in isolation. State whether it must work with general Qi transmitters, a dedicated CowinLink TX platform or a proprietary dock controlled by the same OEM. Also list the transmitter power classes and models used for acceptance testing.
If the product will be sold into an open ecosystem, interoperability has greater weight. If the TX and RX are a matched pair inside an industrial product, the design may prioritize a defined air gap, sealed enclosure or docking tolerance. The engineering route and certification discussion differ, so the intended ecosystem must be clear.
You can review our existing RX wireless charging modules and coils as electrical and mechanical starting points. A catalog module still needs validation in the final stack.
Provide the complete mechanical stack-up
The most useful input is a section drawing through the transmitter coil, product housing, receiver coil and nearby parts. Include dimensions and tolerances for every layer between the coils.
We need to know:
- Maximum RX coil length, width and thickness
- Available PCBA outline and component-height zones
- Nominal and worst-case coil-to-coil distance
- Housing materials, wall thickness and coatings
- Ferrite and adhesive constraints
- Nearby metal, magnets, battery cans, shields or fasteners
- Expected lateral and angular misalignment
- Flex-tail direction and connector location
Coil selection is not just a matter of fitting the largest diameter. Inductance, resistance, quality factor, ferrite and coupling all affect efficiency and temperature. A TI receiver design report, for example, warns that coil and shielding choices influence thermal performance, FOD and coupling. Those relationships are visible quickly when the complete stack is tested.
Decide whether the RX output is regulated or battery-oriented
Some receivers provide a regulated DC output for the host product. Others feed a dedicated battery charger or power-management stage. The choice affects efficiency, heat and system behavior.
For a regulated output, define the voltage tolerance across alignment and load. The host should know when the output is valid, and the RX should recover cleanly after a transient or repositioning event.
For battery charging, provide the charger IC or required charge profile. Do not assume the RX module can replace all battery-safety and charging functions. Battery protection, temperature monitoring and charge termination remain product-level responsibilities unless explicitly included in the module design.
Set thermal limits at the product level
The RX coil, rectification stage, regulation components and battery can all generate or receive heat. A sealed product may have no airflow, and a wearable or handheld device may have strict surface-temperature limits.
State the ambient range, maximum internal temperature at critical parts and maximum accessible-surface temperature. Describe the worst realistic load and charging duration. If the product can operate while charging, test that case; active electronics can raise the internal baseline before wireless-power losses are added.
During development we record temperature and useful DC output over time. This separates genuine efficiency improvement from simple power reduction. The final firmware or host logic should have a defined response to thermal limits.
Include protection and fault behavior
The receiver specification should describe abnormal conditions, not only normal charging. Depending on the application, review:
- Output overvoltage and overcurrent behavior
- Short-circuit protection and recovery
- Overtemperature threshold and hysteresis
- Undervoltage or weak-coupling behavior
- Load disconnect and reconnection
- Reverse-current paths from the battery or host rail
- ESD exposure at accessible connectors
- Host communication or power-good indication
For medical, industrial or other regulated end products, the OEM’s system-safety process may require additional controls. Wireless charging does not replace the compliance obligations of the complete device.
Plan FOD with the transmitter team
Foreign object detection is normally managed on the transmitter side, but the receiver construction affects the system loss that the TX observes. Coil resistance, shielding, nearby metal and alignment all influence the result.
If the OEM controls both sides, TX FOD calibration should use representative RX production samples and worst-case mechanical stacks. If the receiver must work with third-party transmitters, the interoperability matrix should include a range of certified products relevant to the market.
The WPC explains that a coil, shield or IC is not independently a Qi Certified product. Even components used in a certified design do not automatically make a new system compliant. This is one reason we avoid describing an untested custom board as certified simply because it uses a familiar controller.
Define the electrical and mechanical interface
The drawing should show connector type, pin assignment, cable or flex length, bend radius, mounting holes and keep-out areas. Add mating-cycle requirements if the RX is serviceable. If it is permanently installed, define the bonding process and strain relief.
For the host interface, document power-good, enable, interrupt or communication signals. Specify logic levels and sequencing. Ambiguous enable behavior is a common source of prototypes that work on the bench but fail during the host product’s startup sequence.
Turn requirements into an acceptance test
An approval statement such as “charging is OK” is difficult to reproduce. A better sample report contains measured limits and test conditions.
We recommend agreeing on:
- Output voltage/current at nominal and limit alignment
- Efficiency at several load points
- Thermal steady state at defined ambient conditions
- Startup, repositioning and fault recovery
- Operation with the required transmitter matrix
- Coil and PCBA dimensional inspection
- Firmware or configuration identification
- Pre-compliance or certification evidence required for the project
For mass production, convert critical characteristics into incoming and end-of-line checks. Coil inductance and resistance, PCBA function, output regulation and assembly orientation are typical controls. The exact list should follow the risks found during development.
What to send with an RFQ
For a useful quotation, send the product drawing, receiver space, target output, load profile, battery details, transmitter environment, annual volume and required compliance markets. Indicate whether you need only a PCBA and coil or also firmware, mechanical parts, assembly and validation support.
CowinLink’s custom TX and RX development process can begin from an existing platform or a product requirement. If the design is confidential, a simplified stack drawing and performance table are enough for the first technical review. Use the project enquiry form to share the application and we will identify the missing inputs before proposing hardware.
Custom wireless charging receiver module: a practical factory conclusion
The best receiver specification is not the longest document. It is the one that connects electrical output, coil geometry, product stack, temperature and validation in measurable terms. When those items are clear, the factory can make responsible trade-offs and the OEM can compare samples on evidence rather than appearance.
Starting with the full product context usually saves more time than starting with a board outline and target wattage. Wireless power is a coupled system; the specification should be coupled too.
