FFU Fan Controller PCBA Engineering Example

Requirements for a filter fan unit controller

This example concerns a signal-control module for a filter fan unit, or FFU. It sends a speed request to a separately specified fan assembly and reads defined feedback. It does not assume the board contains the fan's motor inverter. Obtain the fan manufacturer's interface document before selecting command circuitry: an analog request, PWM input and serial command are different electrical and software requirements.

List the user-setting interface, supervisory connection, fan-feedback output and any display daughterboard. Define who owns startup, local override and lost-command behavior. If multiple FFUs operate together, state whether this board controls one unit or a group. Airflow uniformity, filter condition, acoustic performance and room cleanliness require equipment or installation evidence beyond board assembly.

Design constraints and the command-versus-feedback decision

A speed command is not proof that the fan reached the requested state. The TI AMC6821 documentation provides a component example combining PWM output and tachometer monitoring, including distinct control modes. It supports the architectural distinction between a commanded duty cycle and observed rotation. It is not an FFU reference design and does not establish compatibility with a selected industrial fan.

Specify command polarity, signal reference, frequency where relevant, feedback pulse format and disconnected-line behavior using the actual fan data. A non-rotating fan and an absent feedback wire may look similar to a pulse counter, so the product owner must define the diagnostic limits. Keep fan power connections distinct from low-level command and display interfaces in the schematic and assembly drawing.

Reference configuration and a tachometer calculation

Hypothetical calculation: assume the specified fan produces two tachometer pulses per revolution and the controller measures 60 pulses per second. Rotational speed is 60 ÷ 2 × 60 = 1,800 revolutions per minute. The pulse count must come from the actual fan documentation. Even a correct speed result is not an airflow measurement; filter loading and system resistance require separate evaluation.

Mixed-technology assembly and procurement choices

Define whether the control and display boards are separate assemblies or one delivered module. A shared interboard connector requires agreement on mating direction, stack height, standoffs and tolerance. Identify large through-hole parts by seating height and orientation. Review whether their leads, connectors or fasteners obstruct another board after the module is assembled.

Procurement should control connector series and mating parts, not only pitch and pin count. An alternate can change latch position or stack height. Mark module-level hardware and any cable separately in the BOM so it is not silently omitted from a board-only order. Use DFMA preparation to review insertion, soldering access, mounting order and inspection access for the actual assembly.

Verification matrix for the board and assembled module

A pulse simulator can establish scaling without running a fan. A representative fan test is separately needed for command compatibility, startup and feedback behavior. A full FFU test adds the installed housing, filter and airflow measurements. Describe these stages explicitly in the test scope, including who supplies each fixture and what evidence is retained.

Handoff documents and an example module record

Supply PCB and assembly files for both boards, the fan interface document, interboard pin table, module drawing, firmware hashes and test procedure. Include user-setting units and any conversion between a displayed percentage and the actual fan request. Specify whether calibration or installation settings are stored on the main board, daughterboard or supervisory device.

A proposed record template is: main-board serial; daughterboard revision; firmware hashes; fan-interface variant; requested setting; measured command; simulated pulse rate; calculated speed; diagnostic state; disposition. Values in that template are not results. Submit the package through a project inquiry and separately identify fan supply, module assembly, airflow measurement and installation commissioning.