LTC7803 in LTspice (Disable briefly)

[Flyback]

Hi,
We want to disable our Buck (LTC7803) then re-enable it, and have it come back on within 1ms......the attached LTspice shows that pulling down the TRACK pin is the best way of achieving this.
Would you agree this is the best way?......Alternatively pulling the RUN pin to between 0.7V and 1.2V is the other way, but results in massive overshoot when re-enabled...would you say this is correct, as often they dont bother modelling the RUN/TRACK pins correctly in LTspice?

 

[crutschow]

as often they dont bother modelling the RUN/TRACK pins correctly in LTspice?

Why to you think that?

I would use which ever inhibit input works best in simulation.

 

[Tony Stewart]

The LTC7803 regulates the VFB voltage to the lesser of 0.8V or the voltage on the TRACK/SS pin. An internal 12.5μA pull-up current source is connected to this pin.

A capacitor to ground at this pin sets the ramp time to the final regulated output voltage. The ramp time is equal to 0.65ms for every 10nF of capacitance.

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You still have excess ringing on step loads due to missing phase lead compensation.

 

[Flyback]

Why to you think that?

Thanks, if you run that sim, you can see that having RUN voltage of 1V doesnt stop it from switching...but datasheet says it should.....LTspice sometimes doesnt bother doing all features...eg, famously, at least in the past, the SYNC pins were never modelled....so you'd put a SYNC signal in...and it'd do nothing.

 

[Tony Stewart]

Make the design work without the SYNC 1st, the SS does work in LTSpice but only if all other inputs are in the nominal range

 

[ChrisP58]

Build it and test.

 

[eTech]

Thanks, if you run that sim, you can see that having RUN voltage of 1V doesnt stop it from switching...but datasheet says it should.....LTspice sometimes doesnt bother doing all features...eg, famously, at least in the past, the SYNC pins were never modelled....so you'd put a SYNC signal in...and it'd do nothing.

Actually, the "RUN" pin does work.
But the simulation of that function is rather poor. If the voltage is changed to 1v, the switching stops but only after some delay, during which, the controller struggles a little trying to maintain a constant output voltage.

The "TRACK/SS" pin shouldn't be used to shutdown the output. That's not it purpose.
Its used to cacade (track) the startup of multiple controllers or, to provide slow startup of a single controller.