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TPS2590 low current settings

Vlad Sergeyev
Prodigy 120 points
Other Parts Discussed in Thread: TPS2590

Hello,

The datasheet does not specify the lowest limit for the current settings. It contains just 3 examples.

My circuit utilizes TPS2590 with the following parameters:

  • Vin = 8V
  • Cout = 2.2uF
  • DC load = 150 R
  • RRFLT = 500K ( I= 0.4A)
  • RLIM = 250K (I= 0.8A)

 

Normally load takes just 53mA (8V/150R), but in fault condition it may be short; so the TPS2590 is used just as a protection circuit. Is it going to work reliably with such low normal current and the fault current threshold of 0.4A that is less than 1A example in the datasheet?

Thanks,

Vlad

  • 0
    TI__Genius 9415 points

    The lowest current limit setting ia 1A to keep the datasheet accuracy specifications. The part can run below 1A but the lower settings have greater unspecified tolerance. The datasheet accuracies are across all parts and across the full operating temperature. operating at .8A may be ok for some applications.

  • 0 in reply to Bob Kando
    Prodigy 120 points

    The design with low current settings described above was propagated into production pilot run (~150 chips installed). One chip failed to operatedat these current settings. It oscillates the output power as if an over-current condition detected. The actual current is less than 50mA. Changing RFLT to 300k (IFLT=0.67A) did not help. But mysteriously changing RLIM to 150k (ILIM=1.3A) helped. According to the datasheet description, ILIM setting should not affect a fault condition but only limit the inrush current. In addition, the voltage on ILIM pin is 1.18V while on other "good" chips it 1.00-1.06V. Could you please comment on this?

     

  • 0 in reply to Vlad Sergeyev
    TI__Genius 9415 points

    ILIM tends to work like IFLT if IFLT is not set. With the wide current accuracy on the part when it is programmed below 1 amp, the ILIM may have actually been set lower than the internal setting of IFLT making ILIM the dominant setpoint.

    The voltage at the programming resistors is a result of a constant current passed through the resistor. It seems the 1.00 to 1.06V levels are not discriminated by internal comparitors. I think your "good" chips are still good but the programming level should be set above 1A.  

  • 0 in reply to Bob Kando
    Prodigy 120 points

    It seems that operation at low current settings is related to tolerances of the chip. We send a significant amount of boards with low current settings to a customer. Therefore, if a particular chip is tested and works on the particular board, is it going to work the same way without changing characteristics and tolerances over a lifetime span?

  • 0 in reply to Vlad Sergeyev
    TI__Genius 9415 points

    It would tend to follow that parts passing your lab tests would work for customers with the exception of temperature difference between your lab and your customers environment.. It may be a risk as we are operating just lower than spec bottom.