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TPS54340: TPS54340, Switching frequency not controllable.

Daniel Pronovost
Prodigy 20 points
Part Number: TPS54340

At first glance, beside a larger regulated voltage error that assumed, everything’s seem to work fine as the circuit can drive various load without problem but when I look at the frequency at which the SW pin toggle, it is around 362kHz instead of more than 1Mhz as I choose an RT resistor of 68k. Moreover, I just remove that RT resistor and the frequency did not change at all! Could it be a bad controller? When I look at the signal on pin RT/CLK what I should see?

  • 0
    TI__Guru**** 191445 points

    With RT = 68 k you should see the switching frequency about 1400 kHz.  If the voltage at the feedback pin falls below about 0.4 V, you could be in divide by 4 frequency fold back and see around 350 - 360 kHz.  If you remove RT resistor (NOT recommended), the frequency should drop below 100 kHz.  In RT set mode, the RT pin has about 0.5 V on it and the switching frequency is set proportional to the sensed current out of the RT pin.  It sounds like your IC is damaged.  Also you need to be careful about layout.  The RT pin function is quite sensitive to noise as the resultant current in the RT resistor can be very low.

  • 0 in reply to JohnTucker
    Prodigy 20 points

    Hi John

    Thanks for your answer.

    I just find the source of my problem. The voltage on EN pin was higher than the specification. I didn't took into consideration the current going out of the pin when designing the voltage divider.

    Dan