Common Mode Choke Selection for ADM3057E

Hi, I am a DFAE.

One of my customers currently use the CAN transceiver IC ADM3057E for his project and he is currently using the Common Mode Choke , ACT45B-510-2P-TL003, which is suitable for a common CAN bus application on his CAN Bus lines (CANL and CANH). But he intends to use this CM Choke, LCFE121002A900TG which is normally used for USB application and he wants to replace this choke because of ESD protection feature. Is it possible to replace ACT45B-510-2P-TL003 with LCFE121002A900TG for CAN bus application?

Thanks so much and looking forward to your reply.

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  • +1
    •  Analog Employees 
    on Jul 30, 2021 9:32 AM

    Hi Anthony,

    First I think it's important to highlight that the ADM3057E has built-in IEC 61000-4-2 ESD performance on the CANH/CANL pins to meet Level 4 requirements (8 kV contact, 15 kV air discharge) without any external components (even for zapping the IC pins rather than a board level port).

    I do not think the USB common mode choke will be helpful for common mode noise associated with CAN communication (few MHz frequency). Comparing the two, we can see that the original choke is specified at 10MHz for minimum 1kOhm impedance, whereas looking at the typical curves for the latter, it has typically about 10 Ohms of impedance so it will leave any common mode noise in the low MHz range pretty much unchanged rather than attenuated as desired.

    However, it's not always necessary to use a choke depending on the system level requirements, so they may find the system still fulfils the requirements with the new one - just that they are placing the new choke on the board for little effect. In theory the customer may want to block out high frequency noise (100s MHz -> GHz) from CANH/CANL if there's something else in the system could be affected at those higher frequencies and some reason to expect the high-frequency noise on the cable (unlike USB 2.0 high-speed, the actual communications won't generate those frequencies).

    Best regards,

    Conal

Reply
  • +1
    •  Analog Employees 
    on Jul 30, 2021 9:32 AM

    Hi Anthony,

    First I think it's important to highlight that the ADM3057E has built-in IEC 61000-4-2 ESD performance on the CANH/CANL pins to meet Level 4 requirements (8 kV contact, 15 kV air discharge) without any external components (even for zapping the IC pins rather than a board level port).

    I do not think the USB common mode choke will be helpful for common mode noise associated with CAN communication (few MHz frequency). Comparing the two, we can see that the original choke is specified at 10MHz for minimum 1kOhm impedance, whereas looking at the typical curves for the latter, it has typically about 10 Ohms of impedance so it will leave any common mode noise in the low MHz range pretty much unchanged rather than attenuated as desired.

    However, it's not always necessary to use a choke depending on the system level requirements, so they may find the system still fulfils the requirements with the new one - just that they are placing the new choke on the board for little effect. In theory the customer may want to block out high frequency noise (100s MHz -> GHz) from CANH/CANL if there's something else in the system could be affected at those higher frequencies and some reason to expect the high-frequency noise on the cable (unlike USB 2.0 high-speed, the actual communications won't generate those frequencies).

    Best regards,

    Conal

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