Changes between Version 12 and Version 13 of fcc

01/03/2019 12:13:12 AM (10 months ago)
Ryan Erbstoesser

add more info for pi filter


  • fcc

    v12 v13  
    332332Conducted emissions are those that are on a conductor, such as a power or ethernet cable . In the case of using an AC to DC converted connected to a wall, the converter will provide protection. The majority of our customers typically use an AC/DC supply to generate the DC voltage to our board so the conducted emissions are tested on the AC/DC supply and not directly on our DC input. If using an external power supply, explore the option to have the testing done on the AC input of that supply.
     334The DC/DC converter we use on some of the Ventana boards does have a switching frequency at 280KHz so this will show up on conducted emission testing. In most cases customers are using an AC/DC converter so the conducted emissions is measured on the AC input main instead of the DC. For cases where the DC needs to pass we suggest they use an input filter.
    334336Common solutions include:
    335337 * Install a ferrite around the power cable
    336338 * Typically a large in-line inductor (around 22uH on +VCC input) will provide enough filtering. Note that this inductor has to be sized to handle the amount of current the board is drawing under load. Locate it as close as possible to the board. Note that the inductor will slow the rise/fall time of the input voltage so test with a particular configuration to make sure there are no start-up issues. These inductors can be quite large, especially for high current applications.
    337339  * Here would be a suggested example part: []
    338  * Put a Pi filter inline with the power cable, such example is below:
     340 * Put a Pi filter inline with the power cable, such example is below (values may need to be adjusted)
     341  * Note that the component values would need to be tested and make sure they don’t cause any adverse effects in your system. The use of an inductor in series slows the transient response of the input voltage so when radios transmit this could cause the DC/DC to “starve” for voltage. It is best to setup the Pi filter and then do some testing (actually put a scope probe to the input voltage at the board) and make sure there isn't any visible large dips during radio transmit.
     342  * Input caps: 10uF/100V
     343  * Series Inductor: 22uH, >6A rated
     344  * Output caps: There typically is 10uF of capacitance on the board but an additional 10uF/100V would be good if possible.
     345  * Here is the topology:
     346   * Input -------caps to gnd ------- series inductor ------- caps to gnd----- output to board
     347  * Example schematic:
    339348  * [[Image(pifilter.png)]]