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Constant off time control chips for SMPS?

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treez

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Hello,
We wish to design a constant off time controlled SMPS. There are virtually no constant off time control ICs on the market, so therefore we have to make our own. Unfortunately, all of the components shown here are required, and it’s a lot of components.
Do you know of any Constant off time controllers for SMPS?

(LTspice and pdf schem attached, of a "discrete" contstant off time controller)
 

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  • Constant off time boost.txt
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National Semi, now TI, has several constant-on time controllers.
The reason being that, if one uses a feedforward of the input voltage to inversely control the Switch's on-time, one may have ultra-fast transient response.

What would there be the reason to employ a constant-off time controller?
 
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Thanks, with constant off time you dont need slope compensation.

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constant on time controllers are good, but as you know often the on time is limited by saturation of the inductor...in other words, there is a peak current limit, even with constant on time controllers, so the on-time is not always constant at "t" seconds, but often ends up being less than "t".
 

Thanks yes Venables gives the way of making ucx84x controllers have constant off time...of course, these controllers have a high current sense ref voltage, and as you know , this can mean too much loss in the sense resistors...its a shame no controllers with lower sense ref voltages cant be made constant off time.
 

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