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TPS54260 frequency division

Yalcin Haksoz
Prodigy 10 points
Other Parts Discussed in Thread: TPS54260

I am using TPS54260 in a battery charger circuit. (10 to 15V in 8.4V at 2A out). It is programmed to run at around 250kHz with a 470k at RT/CLK pin. Everything is perfect until I check the operation at overload and short circuit.

The device is supposed to reduce the frequency as the voltage at the Vsense pin drops. At short circuit the frequency is expected to be divided by 8 and be around 30kHz. Unfortunately I can not see that happening. I have checked this on 4-5 devices and they all behave the same, even at short circuit the frequency stays at 250kHz and after a few seconds the device fails. I checked that also on the evaluation unit and it works fine, the frequency drops to ~30kHz from ~250kHz when the output is shorted. My circuit is not different than the evaluation unit except the output voltage is programmed differently but at short circuit it doesn't matter.

Now my questions are: Has anyone else observed this? Is there anything in the device that can disable frequency division feature? What might I be doing wrong? Why the temperature protection in the device did not work and I always ended up with a dead device? Do I have a bad batch of samples?

Thanks,

YH

  • 0
    TI__Guru**** 191445 points

    I have not seen this before.  You state that the function works as expected on the evaluation board.  It may be possible that you have some bad devices.  I recommend that you contact your local AFA and submit one or more for failure analysis.  In the mean time you can try to gradually increase the load above the current limit.  Monitor the switching node and VSENSE verify that as the current increases the voltage starts to fold back and that the frequency falls to 125 kHz when the VSENSE voltage reaches .6 V and 62.5 kHz when VSENSE falls to .4 V, etc.  Let me know what happens.