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LMR14030: LMR14030 test problem base TPS254900Q1EVM-817 EVM

user4206199
Intellectual 470 points
Part Number: LMR14030

Picture 1：Input surge current wareform,Vin(Yellow),Iin(Pink)

Picture 2:Power down wareform,Vin(Yellow),Vout(Blue),Vss(Violet),Iout(Green)

Picture 3 Power on wareform,Vin(Yellow),Vout(Green),Vss(Blue),Iout(Pink)

 

My question as below

1)      As picture 1：Our power can produce a big surge current and approach 10A and it can damage IC or not?Input terminal of LMR14030 have a limit for input surge current?

2)      As picture 3:why Vout terminal have curren overshoot when power on?this curren can achieve 6A,how to avoid?and why overcurrent protect mode not start-up?

3)      Accouding to specificitions,LMR14030 will enter Sleep mode when load current at below 300mA.but we find it work DCM mode when load current at 100mA,why?pls help exaplain it

4)      LMR14030 switch frequency will gradually increase when power on,Why?

5)      As picture 2: Why output volage have osicillation phenomenon when power down.It can avoid output voltage appearing osicillation phenomenon if I adjust enable terminal resistance?

  • 0
    TI__Expert 5745 points
    1) How did you measure the Iin and Vin? Pls put the probe close to the input cap. And do you use a long cable for the input? If yes , pls add a big cap (220uF) at the Vin to avoid the oscillation.
    2) I think the Vout current overshoot is caused by the surge current, so see the waveform again after adding a big cap. And the High-side MOSFET have the over current protection, the I-lim is in the 4.4~~6.6A which may not trigger the protection.
    3) Please show me the waveform of the SW when the I=0.1A.
    4) It's normal for the frequency increase during the after power on. The IC need time to adjust the duty and frequency cycle by cycle .
    5) The main reason is the Vin is not stable , when you add a resistor at the EN pin which is same as adding a LF to make EN stable.
  • 0
    TI__Mastermind 27045 points
    Hi

    Below comments on your questions:

    1) As picture 1：Our power can produce a big surge current and approach 10A and it can damage IC or not?Input terminal of LMR14030 have a limit for input surge current?-----------------The Abs Max Vin voltage is 44V, add more caps on input if the peak voltage exceed 44V by surge current.

    2) As picture 3:why Vout terminal have curren overshoot when power on?this curren can achieve 6A,how to avoid?and why overcurrent protect mode not start-up?-----------I think you start up the circuit with E-load at CC mode, the inductor current waveform is correct as it need to charge up Cout to track the SS voltage and provide load current at mean time. pls change E-load to CR mode, or us epure resistor load.

    3) Accouding to specificitions,LMR14030 will enter Sleep mode when load current at below 300mA.but we find it work DCM mode when load current at 100mA,why?pls help exaplain it---------300mA is peak current, 100mA is average load current, they are same thing with proper Vin/Vout/Fsw/inductor condition.

    4) LMR14030 switch frequency will gradually increase when power on,Why?

    5) As picture 2: Why output volage have osicillation phenomenon when power down.It can avoid output voltage appearing osicillation phenomenon if I adjust enable terminal resistance?-------------------it caused by high source resistor of input power supply, Vin goes back little higher than UVLO once IC stop switching(no input current). it can be resolved by program system UVLO on EN pin, refer to data sheet 8.3.6 section, program hysteresis higher than 1V.