UCC256402: Loop gain equations for the UCC256402

Hi,

Can you clarify what is Ires in your question?Is it the resonant current? 

Hi Hong Huang

the datasheet claims: "Hybrid hysteretic control (HHC) – Best-in-class transient response" - but there is no detailed design how to get to the "best in class transient responce"

lets take the eval board UCC25640EVM-020 as example.

user guide: : SLUUBX3B

whats the gain from FB node to resonant current in C1/C17?

the compensation circuit around TL431 gives a zero: R22/C26, a pole C25/R22, the mid frequency gain R19/R22 - those are selected to give a certain responce - but its not shown in detail how? the measured loop gain is shown, but not the model for it or calculations to get to it.

is there a ac-pspice model? or even a transient model

best regards

kim

Hi,

On HHC, can you review the datasheet section 8.3.1? HHC design is related to VCR. 

On the feedback loop compensation design, I am contacting the designer of the EVM to know how the EVM feedback loop compensation is designed. I will provide that after I get it.

Hi Hong Huang

yes section 8.3.1 talks about the design of the HHC, but there are no equation for gain from VCOMP (FB) to the resonant current. 

it states:

"In summary, HHC solves the following problems: • Help LLC converters achieve superior load transient and line transient • Changes the small-signal transfer function to a first order system to easily achieve very high bandwidth • Inherently stable via frequency compensation"

so if its a first order system, there should be a equation from the FB node to current in the resonant circuit.

it will be good to get the EVM feedback loop design.

thanks

kim

hi Hong Huang

is there a spice model available for the UCC256402?

rgds

kim n madsen

Hi,

We do not have a Spice model. But we have a Simplis model

https://www.ti.com/lit/zip/slum684

The first order system model based on our analytical development is like the below. In general, Type II compensation is ok to use to compensate a first order system.

The EVM uses a Type III compensation to make performance adjustment such as to achieve wider bandwidth.

Hi Hong Huang

Thank you for the link to the simplis model - will there be a TI-spice model? we dont have the Simplis program.

where you able to get the EVM loop design?

Best regards

kim