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LM5017: EN60950 CREEPAGE STANDARDS TROUBLE

user3928443
Prodigy 60 points
Part Number: LM5017

We are using the LM5017MR to DC/DC convert a max Vin of 71 Volts to 15V.

All is working fine for the functional point of view.

Our doubt if about normatives (CE)

Under the new RED Directive (2014/53/EU for radio telecommunication equipment) the safety directive applies with no limits of Voltage. In our case this means that the EN 60950 normative must be checked and be compliant with.

For this kind of input this european  standard there is a point taht we need to clarify :

The CLEARANCE distance for this Vin (71 Volts) is 0.4 mm. There is no problem with this point, as the pins clearance between VCC and GND for this is 0.78mm.

Problem arises with CREEPAGE distance, where distance required is increased to 1.2 mm in normal conditions (Normal Conditions are a device with Pollution Degree II, Material Group IIIa or IIIb, and uncoated PCB).

Under this specs, there is nothing to do with the PCB design, because the IC itself does not comply with 12mm of distance).

The only way to get compliant with CREEPAGE is :

To design the equipment under Polution Degree I. (Creepage dissapears and only clearance is mandatory).

To Coat the PCB and the IC (use some kinf of Varnish). UNder this condition CREEPAGE goes down to 0.1 mm

Are we missing something?

Anybody has some experience or ideas about this subject, where an IC with 100V of input does not comly with international standards in normal conditions?

Thanks in advance

  • 0
    TI__Guru 73752 points

    Hello,

     

    Thanks for your question. TI generally recommends consulting with a qualified safety engineer for advice to determine the requisite creepage and clearance requirements for your particular design as there are a number of factors that contribute to the required limits and each case needs to be carefully considered.

     

    That caveat notwithstanding, one interpretaton is that the EN60950 standard may typically apply in terms of product safety across the isolation barrier (from primary to secondary) using recommended clearance and creepage distances, thus achieving a particular grade of insulation/isolation (e.g. basic, double, supplementary, etc.). It may not specifically pertain to VIN and GND nodes referred solely to the primary side of the DC/DC converter as this spacing is usually guided by IPC standards for PCB layout.

     

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 60 points

    Thanks Tim.

    as far as I know, (Not being and experte), EN60950 not only applies from primary to secondary parts of the circuit. As you say, the "kind" of parts determine the amount of Clearance and Creepage in function of the required isolation (Functional, Basic...).

    This standard also applies to parts of the primary side between primary side, where the required isolation is "Functional".

    This Creepage and Clearance distances I posted before are for this kind of Isolation (Functional), between conductors in the primary side.

    An interesting web page ( creepage.com  ) helps a lot in determining these values.

    Thanks again.