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UCC28780EVM-002: Unable to start up when connected to power
Part Number: UCC28780EVM-002
I have a doubt regarding the feedback current (Ifb), it is not clear to me from the datasheet that Ifb should be between 0-75uA. At what value of Vout, what should be the value of Ifb, that I am not understanding. For eg., If nominal output is 20V, then at 20V should the feedback current be 50uA or 75uA or 0uA or what? at which exact value of Ifb, the control unit will consider the output is as per required? Please help me with this query.
Could you provide me in detail the range of the Rdm and Rtz? As in the following description from the datasheet, it says about too small and too large current, could you specify the limits ? And also what is the voltage level to check the pin open or short condition?
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In reply to Mike O':
I discuss the RDM and RTZ with the design engineer. He said that if you design for applications between 5 W and 150 W, you should not have an issue in regards to triggering open/short pin protection.
In regards with how IFB current moves with control law I discussed this with the system engineer. Please refer to figure 23 of the data sheet.
At Io max, IFB ≈ 0uA
AAM, IFB 25 uA to 0uA
ABM, IFB ≈ 25 uA to 35 uA
LPM, IFB ≈ 48 uA to 35 uA
SBP, IFB ≈ 75 uA to 48 uA
Io = 0A, IFB ≈ 75 uA
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