Looking for a CRM Buck controller with operation frequency up to 700kHz or 1MHz

Chen,

What input voltage range, output voltage and output current do you require?  If you use a non-synchronous controller (no LS FET), CRM operation will depend on the load current always being greater than one half the peak to peak inductor ripple current.  Any other features you need?

Hi John,

thank you. The input voltage range is from 750V-900Vdc. the output voltage range is 350Vdc-750VDC. 1500W output power.

We will have independent Aux power for the controller. There are external MOSFET and diode as well. To achieve ZVS, I need a controller for CRM MODE instead of CCM. high power loss of hard switching in CCM will kill my mosfet. thanks.  

Chen,

My group will not have any product to support that high voltage.  That input voltage is unusually high. Can you give me some details about your application?  Maybe I can point you to a solution,

Hi John,

Sorry, I am confused. Even it is a high voltage application, the controller gets low voltage feedbacks. Then it provides a PWM signal(low voltage). I don't expect the controller IC to handle the high voltage. thanks.

Chen,

Please examine this TI high voltage reference design.  Your application can likely be a modified version of it.

www.ti.com/.../PMP10415

Hi John,

Thank you. So you recommend me to try UCC28700? But it is a Discontinuous Conduction Mode (DCM) with valley switching with a maximum switching frequency of 130 kHz.

I need a CRM mode controller with a max switching frequency up to 700kHz or 1Meg Hz.

what is the max switching frequency of UCC28811? Thanks.

Chen,

DCM Is what I understood you wanted.  For that extremely high VIN range, you may need a lower switching frequency.  I proposed your input range to our Power Design Services group and they recommended the PMP10415 reference design.  Generally, I can only directly support VIN of less than 30 V.  Can you provide more details about your requirements?

John,

Sorry, CRM means critical conduction mode or boundary conduction mode. then the peak current stress will not so high. RMS current will be lower than DCM, too. the power density requirement is high. I need to run it at high frequency to reduce the size of magnetics and output filter. So ZVS operation is required. CRM operation mode is selected.

I am looking for a controller. no need to have the ref design. all the other design was done already. there is cost limit so I can not use my DSP so I need a analog controller with low cost.

Probably, UCC28811 can do the job. but need to check the max frequency limit. it is not mentioned in TI UCC28811 datasheet. can you please help to check? thank you.

Chen,

Let me see if I can reset this thread.  My group does not support these high voltage applications.

John,

Thank you. if it is necessary, please also copy your related group. thanks 

Chen,

UCC28811, is probably not what you are looking for.  It is self oscillating, probably at a relatively low frequency probably around 100 kHz in typical applications.  You may find that high frequency operation is difficult to achieve.  What power FET are you using?

John,

Thank you very much especially for your warm advices. Yes, switching loss will increase with a higher DC bus. I am experienced on high voltage designs.

I would like to use the TZE in the controller like UCC28811 to achieve the CRM operation of the Buck converter.

What is the upper limit frequency for UCC28811? probably I can use 500kHz switching frequency.

If it is still not good enough for 500khz operation, do you have recommended part number from TI? Thank you again.  

Chen,

The PWM circuit is self-oscillating with the turn-on being governed by a transformer zero energy detector (TZE pin) and the turn-off being governed by the current sense comparator.  So the actual frequency will depend on your implementation.  I do not see any particular upper limit.  It will be determined by your magnetics design

Hi John,

Great! it is the controller I am looking for. seems the upper operation temperature is 105degC. do you have 125degC version. Thank you.

Hi John,

Thank you very much!