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TMS3705: Need help with calculations for SFB/SENSE resistor divider

Gerd Christian Knese13
Intellectual 410 points

Part Number: TMS3705

Dear TI team/users,

I try to improve the reading distance of the TMS3705 by increasing the voltage of a design similar to "RI-ACC-ADR2-10" at the driver up to 24 V.

I know, that I have to change the TVS diodes and the type of driver to one, that can be used at 24 V.

But, what about the resistor divider between the coil and SFB/SENSE (150k/47k).

I can't find proper information how to calculate thiese values for higher voltages.

Please help!

Kind regards

Gerd Knese

  • 0
    TI__Mastermind 18265 points

    Hello Gerd,

    the resistors are used to set the gain for the RX input amplifier. This gain should not be higher than 5. Currently it is set to 150k/47k = 3.2.

    If you want to increase the reading distance with a higher TX field-strength it my be necessary to implement also a pre-amplifier for the RX path to maintain a sufficient RX input level at SFB of min. 5mVpp. In addition the maximum values given in the datasheet should not be exceeded.

    More information can be found here:

    https://www.ti.com/lit/pdf/scba020 

    Best regards,

    Helfried