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Vfb and Vioc when connected to a SEPIC

Category: Datasheet/Specs
Product Number: LT3041

Hello 

I have some questions related to building  LT3041 arrays in Voic configuration...(Assume R1=Vfb resistor, R3 = limit Vmax, and R2 )

1. Is it correct to assume that the value of Vref in any Vioc type scenario (in this case its LT3759 with +1.6V = Vref and -0.8V for negative) represents ultimately the Voic limit?

If Voic=Vfb(R1+R2/R1) then the smallest ratio is when R2 = 0. Which then sets Voic = Vfb.

Please advise 

2. When calculating the proper R3 values (for establishing an upper ceiling for Vmax-in)

What specific value is to be applied to Isink ? What is a good practice?  Could you please explain thank you.

R3 = Vmax - Vfb(R1+R2/R1) / (Vfb/R1+ Isink) 
Basically here it says that if R2 is zero then R3 is basically V(max)-V(fb) divided by the sum of I(sink) and I(R1).
For our initial prototype I had assumed 250uA as max I(sink) current. 
3. if we assume an inverting configuration then Vfb becomes -0.8V (with the sister chip LT3099)
Which ostensibly would reduce Vioc significantly in the negative array  (and reduce power loss etc.)
Is there a way to reduce Vioc in the positive regime?
Hope this makes sense.
Please elaborate. Thank you

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  • Hi Ryan

    Yes I had mentioned the LT3099 in my query. It is part of the INVERTING design to supercede the LT3080-1. The LT3099 provides the same Vioc functions except with reversed polarity. The goal is to create voltage architectures that scale to 50W and are easy to set. 

    Noted regarding R3. for 12V out set to 15V max.

    Thank you 

    (PS. I have a query into the support team to understand why the LT3099 model does not cooperate properly. It simply will not allow programing on the SET pin. 

    At least the MACOS version will not work. Perhaps I am doing something wrong ...)

    thx

Reply
  • Hi Ryan

    Yes I had mentioned the LT3099 in my query. It is part of the INVERTING design to supercede the LT3080-1. The LT3099 provides the same Vioc functions except with reversed polarity. The goal is to create voltage architectures that scale to 50W and are easy to set. 

    Noted regarding R3. for 12V out set to 15V max.

    Thank you 

    (PS. I have a query into the support team to understand why the LT3099 model does not cooperate properly. It simply will not allow programing on the SET pin. 

    At least the MACOS version will not work. Perhaps I am doing something wrong ...)

    thx

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