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[FAQ] SN6505B-Q1: Driving waveform distortion at high ambient temperature

Vincent Chen64988
Expert 4480 points
Part Number: SN6505B-Q1
Other Parts Discussed in Thread: SN6501

Hello team,

My customer put SN6505B-Q1 at 85°C chamber then the output voltage became abnormal. Please find below waveforms.

SN6505B-Q1 is put at current monitoring board and closed to shunt resistor. When the board was put at chamber and large current flowed through shunt resistor, the shunt resistor's temp. is 140°C, transformer is 125°C, SN6505 is 110°C.

The measured point of scope's waveforms were as the upper diagram's, the driving waveform(CH2, green) became distortion at high temperature environment. Could them help to comment it and what experiment we can to dig out the root cause.

Thanks very much.

Vincent Chen

  • 0
    TI__Genius 17100 points

    Hi Vincent,

    Thank you for including waveforms, dataset, and temperature points in this post; they are helpful in deducting a root cause here. If the SN650x system is in one of the typical configurations from the SN6501/SN6505 datasheets, then the output voltage supply might be collapsing (or distorting) due to high reverse leakage current in the Schottky diodes.

    At temperatures above 85dC, many Schottky diodes' reverse leakage current increases into ~1000uA range, and this too high for the system to operate properly (this is due to the current balance that must be maintained in push-pull power supplies). If our customer anticipates that their system will operate in high temperatures, please encourage them to replace the current diodes with low leakage Schottky diodes, such as the RB168MM-40.

    Choosing the appropriate Schottky diodes is an important consideration for push-pull power supplies as mentioned in Section 9.2.2.3 of the SN6505 datasheet. A comparison of reverse leakage currents is shown below:



    This is likely the cause of our customer's issue, but if there is additional information or insight I can provide, please let me know! I will await your response.


    Best,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Expert 4480 points

    Hi Manuel,

    Thank you very much for prompt response, I will suggest customer to try another schottky diode that like you proposed and will let you know the test result.

    Best regards,

    Vincent Chen

  • 0 in reply to Vincent Chen64988
    TI__Genius 17100 points

    Hi Vincent,

    You're welcome! Has our customer implemented low-leakage Schottky diodes and tested their system? Please let me know!


    Thank you for your time,
    Manuel Chavez