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TPS84259 / Transient Responce by high slew rate

Ryuji
Guru 20090 points
Other Parts Discussed in Thread: TPS84259, TPS84A20, TPS84621, THS4601
Hello,
 
I would like to measure Transient Load Responce under condition.
 
<Conditions>
Use TPS84259EVM
Vin:15V
Vout:-3.3V
Iout: 0.1A --->2A
di/dt : 5A/us
 
I configured output current slewrate as 5A/us and 1kHz SW by electronic load and I measured output current by osilloscope.
But, I can't see the 5A/us of slewrate.(please see the attached figure as slewrate)
 
Could you please kindly give me the advice of this reason ?
Are there prasitic inductance in the TPS84259 ?
 
Best Regards,
Ryuji Asaka
  • 0
    TI__Mastermind 28020 points

    Hi Rjuki,

    The EVM does not effect this load step. What model of electronic load are you using? How long is the connection to the load?  I suspect the laod is not actually able to slew at 5A/us rate.

  • 0 in reply to J Arrigo
    Guru 20090 points
    Hello Arrigo san,
     
    Thank you fo the reply.
     
    Cable length : about 100mm at both of Vout / GND.
    Model :PLZ164WL ( this model can set 25A/us of slew rate)
     
    I measured transient responce of 5A/us of TPS84A20 by this constitution.
    So I think that TPS84259 indactance is larger than TPS84A20.
     
    If I construct ideal electronic load and TPS84259 connection, can I measure 5A/us?
     
    Best Regads,
    Ryuji Asaka
     
  • 0 in reply to Ryuji
    TI__Expert 7599 points

    here are my 2 cents....TPS84259 has a negative output..... I dont know much about your electronic load but I think you will have to reverse the sign of current.. as in -5A/uS ? TPS84A20 has postive Vout and maybe that why its working...?

  • 0 in reply to Arjun_Prakash
    Guru 20090 points
    Hello Arjun san,
     
    I used attached pdf's constitution.
    I understood that TPS84259 is negative output module.
    So, I connected GND to Positive of Electronic load and Vout to Negative of Electronic load.
     
    I connected Vout to Positive of Electronic load and Gnd to Negative of Electronic load when TPS84A20 measument.
     
    Does this structureing effect to measuremnt of TPS84259?
     
     
    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ryuji
    TI__Mastermind 28020 points

    Hi Asaka san,

    Yes, I was able to verify that a fast load step (5A/us) can be measured on the EVM.

    This device was not designed for fast transient response. Additional bulk capacitance is required to have any acceptable voltage deviation.

  • 0 in reply to Ryuji
    TI__Expert 7599 points

    Asaka-San,

    Your description should work fine..Your current probe might add some inductance which can lower your slew rate..

    I looked at the datasheet but could not find any reference to transient testing....

    I would let the device champion comment on it...

    For my application I have used tps84621 and tested current surges using my own Electronic load circuit as I needed 1A/20nS current surges.. As the regulator are not built for fast transient I had to rely on output caps to control my voltage deviation..... I built my electronic load using a THS4601 High speed Amp, A power MOSfet (preferably with low gate charge)and a low inductive high watt sense resistor. I measure the voltage across the sense resistor to confirm the current surges... And I vary my output capacitance untill I get the desired acceptable voltage drop during current surges.