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SN6505B: Diode and P2P replacement

Eric Valin
Prodigy 40 points
Part Number: SN6505B
Other Parts Discussed in Thread: SN6501,

Hello TI team,

I need to implement an isolated CAN Bus node based on the spec sheet recommended design of the transformer driver SN6501 or SN6505B.

Question 1

If not used, can pin 6 (CLK) of the SN6505BDBVR be directly connected to GND to use the SN6501DBVR as a second source? This is because the SN6505B has a different pinout from SN6501 and the equivalent pin is connected to GND for the latter. The SN6505B specification mentions that the pin is pulled down internally to GND, but I'm not sure if it can be directly connected to ground or left open for the IC to use its internal clock.

Question 2

My load is 100mA. TI recommends using the MBR0520L 20V Schottky diode with a VF of 275mV at 100mA. Due to the high leakage current of this diode above 85°C, TI also recommends using the RB168M-40 Schottky diode with an IR of 4 µA at 20 V and 100°C. Even though the RB168M-40 diode has a low leakage current, its VF is twice as high as that of the MBR0520L diode. Could the PMEG40T10ERX diode be used instead of the RB168M-40M diode for an operating temperature of 105C?

Indeed, the PMEG40T10ERX diode has a leakage current of 800uA (@20V, 100C) compared to around 3000uA for the MBR0520L diode (@20V, 85C) which is still functional without problem with this leakage current at 85C. This compromise is necessary because the VF of the rectifier diode must be as small as possible otherwise the transformer ratio must be increased to respect the minimum Vdropout of the voltage regulator.

Comment

The specification of the SN6505B seems to be a copy paste of the specification of the SN6501.  The specification of the SN6505B needs to be corrected for many sections.

Section 9.2.1; maximum load current should read 600mA

Section 11.1; “The rectifier diodes should be Schottky diodes with low forward voltage in the 10 mA to 100 mA current range to maximize efficiency”.  This sentence does not work if the load is 600mA.

Etc…

Thank you,

 

Regards

 

Eric

  • 0
    TI__Guru 55575 points

    Hi Eric,

    Thank you for reaching out.
    Please allow me to review the questions and come back to you tomorrow with a response, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 40 points

    Hello Koteshwar

    Did you have time to look at my questions?

    Thanks

    Eric...

  • +1 in reply to Eric Valin
    TI__Guru 55575 points

    Hi Eric,

    Apologies for the delay in response. Please see my inputs below, thanks.

    Answer 1:
    Yes, CLK pin can be connected to GND and that is perfectly fine. This does allow the footprint to be compatible with SN6501.

    Answer 2:
    Yes, diode PMEG40T10ERX should be fine to use for rectification. I also understand your concern on increased turns-ratio due to higher VF of diode.

    Feedback:
    Thank you for notifying me about the copy/paste issues. We will make note of these and update our datasheet in our next revision. Appreciate your inputs, thanks.


    Regards,
    Koteshwar Rao

  • +1
    Prodigy 40 points

    Hi Koteshwar,

    Thanks for the answers

    Eric...