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TPS62067-Q1: Load Transient is not as expected.

Amal K Moncy
Prodigy 40 points
Part Number: TPS62067-Q1


Hi Team,

I am getting different Waveforms while doing Load transients on the IC.

Schematics



Test Set-up


Results,

1. Vout = 1.8V, I_load = 1 A, Current rise time - ~680ns

Yellow - V out, Green - Drain Voltage, Blue - Gate pulse, Magenta - Load current






2. Vout = 1.8V, I_load = ~600 mA, Current rise time - ~680ns

Yellow - V out, Green - Drain Voltage, Blue - Gate pulse, Magenta - Load current

Ignore the negative current: Due to the current prob direction.





3. Vout = 1.8V, I_load = ~600 mA, Current rise time - ~1µs

Yellow - V out, Green - Drain Voltage, Blue - Gate pulse, Magenta - Load current






May I know, why the voltage output Behaves like this? supply output going off, both 600mA and 1A load transient. 

Let me know, if you need more info.

  • 0
    TI__Mastermind 23550 points

    Hello Amal,

    If I am understing it right, pink is your load current waveform. It does not look like pulse to me. Is that intended to look like this?

    Thanks,

    Farheen

  • 0 in reply to Farheen
    Prodigy 40 points

    Hi Farheen,

    You can see the supply voltage is getting off ( Yellow ). I hope this is the reason we see current switching or following the voltage.

    I hope I answered your question. 

    Thanks,

    Amal

  • 0 in reply to Amal K Moncy
    TI__Mastermind 23550 points

    Hello Amal,

    Load current is really unstable, that can affect that. In steady state, is it operating fine? I mean with constant load, is the Vout stable?

    I am attaching an example of load transient result from the same device. Can you please tell where exactly load current you are measuring? and What the load current you want to provide? 0-->1A?

    Thanks,

    Farheen

  • 0 in reply to Farheen
    Prodigy 40 points

    Hi Farheen,

    In the steady state, it's operating fine. Yes, with constant load the Vout is stable.

    May I know the current rise and fall time of the transient that you have given? we were trying with ~680ns and ~1µs

    Load current measured points have been highlighted in the Red circle.

    You can see in the Green waveform where the MOSFET is on and drawing current, I think the Vout is going off hence the current goes off and try again to turn On and get off.

    Yes, our requirement is ~ 0 to 1A.

  • 0 in reply to Amal K Moncy
    TI__Mastermind 23550 points

    Hello Amal, 

    The slew rate in the case where I have shared is 2A/us. It is also for 1A max. Can you probe in the right direction and then measure it. I agree with you with the gate current is fine. But the load current is separate. It should not get affected even Vout goes down.

    It can be current is going high and it is touching the current limit if the device and that is why Vout is going down.

    Thanks,

    Farheen

  • 0 in reply to Farheen
    TI__Mastermind 23550 points

    Hello Amal,

    Can you please also add the Vin plot if possible to rule out that Vin is stable? I see 0.57A max written on schematic. Is this the current limit for the circuit or just the peak current drawn by the device?

    Thanks,

    Farheen