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TMUX7462F: RDSon for CAN interfaces, Vfp and Vfn ramp-up and connections

Lenio Cacula
Genius 16370 points
Part Number: TMUX7462F

1. Considering that the typical impedance of a CAN bus is 120Ω, is the maximum on-resistance of 16Ω an issue? My customer designs the system considering the minimum impedance of CAN can reach 60Ω and manifested concern in using the TMUX7462F. Do we have extensive data results for CAN networks? I understand the 16-Ω only occurs at 125°C, but does that mean for CAN the temperature range has to restricted?

2. DS section 8.3.2.4 recommends tying Vfp to Vdd and Vfn to Vss if fault supplies aren't available. Section 10 however suggests a sequence and voltage ramp of Vdd and Vss prior to Vfp and Vfn respectively. Can you comment on why connecting the pins together is not an issue?

Thank you!

  • +1
    TI__Mastermind 29638 points

    Hey Lenio,

    1) We don't have the extensive data you're asking for. The Ron will depend on the supply voltage being used here. Given the +-15V supply, you will see the variation across temperature up to 16ohms. If the system can't handle this variation, and they expect the temperature to reach this level, you may need to look into restricting the temperature range to allow for use of the TMUX7462F in this particular system. However, at a given temperature, the R-on is extremely flat so you'll see consistency there. They could potentially look into adding some offset here in the termination resistor to account for the added resistance from the TMUX7462F but this could come at the expense of impacting other aspects of the system. 

    2) The ramp up sequencing is to ensure that there isn't a case where the VFN/VFP pins are ramped up before the VDD/VSS which would violate the abs max on these pins. Ramping up VDD/VSS first is a safety requirement to ensure that the device doesn't get damaged. When tying the VFN/VFP to VDD/VSS the sequencing won't matter since they'll ramp up at the same time, so there isn't that issue to worry about there.

    Thanks,
    Rami