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TPS4811-Q1: TPS48110 with dual fets common source configuration problem

Anton Bityaev
Prodigy 20 points
Part Number: TPS4811-Q1

Hello,

I have a problem with my design. (schematics is attached). In this design, I've incorporated TPS48110 and common source back-to-back fets (current 2 fets but an option to expand to 8 fets - 4 parallel to each side).

the FETS don't open up and with even 1A of the load (resistive)  the FETS, which are connected to the sense side are hitting up and burning. the circuit doesn't work as it should and the source-gate voltage are jittering of up to 4 volts. The input voltage is 27-30v

The output capacitors are not installed (to eliminate the capacitor's influence). The electronic load is resistive - 1A

The precharge circuit is built by the separate driver (TPSI4050 and other two back-to-back common source fets) with 5 ohm resistor

The strange thing that I see is that the source voltage is 0 vs the ground. 

My questions are:

1. Is the back-to-back with common sources configuration allowed with TPS48110?

2. Any chance that the zener diode (ZD35) connected between the source-gate (for FETs protection) actually causes those troubles? It is rated to 15v

  • 0
    TI__Guru** 105361 points

    Hi Anton,

    Thanks for reaching out!

    Can you follow the below debug steps and try

    1. Check with pure resistive load. Some electronic load may have input capacitance.

    2. Is CBST sizing proper ? Please use design calculator to verify

    3. Probe FLT_I and FLT_T outputs and check

    4. If FLT_T is triggering, connect DIODE pin to gnd and try

    If none of these help, please share better clarity schematic and start-up waveforms (BST, SRC, GATE, INPUT current, FLT_I, FLT_T, TMR)

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Prodigy 20 points

    Hello Rakesh,

    Many thanks for your advice will do and report.

    At this moment could you please provide your view on common sources back-to-back FETs configuration? Is it allowed from a functional perspective? Please confirm.  

  • 0 in reply to Anton Bityaev
    TI__Guru** 105361 points

    Hi Anton,

    TPS48110 supports common source back-to-back FETs configuration

    Best Regards,

    Rakesh