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UCC28742: OVP and VDD from design spreadsheet tool

Part Number: UCC28742

Hi, I have a few questions about the default example in the design spreadsheet


In the design calculator, the overvoltage thresholds are VOUT_OVPnom = 5.3V and VOUT_OVPmin = 5.023V (calc cell C191). 

VOUT_CV = 5V, VOUTripple = 50 mVp-p (cell C163).  This means that that the maximum Vout is 5.025V (not accounting for other tolerances like the voltage regulation error).

So, the worst case Vout by design is already crossing the VOUT_OVPmin.  Should we design the minimum OVP threshold higher than the maximum Vout during normal operation?


Is there an internal voltage clamp at the VDD pin to limit the voltage during start up charge from VBULK to VDD via RTRICK?


  • Hi Kelvin,

    Q1. Yes you are correct. Minimum OVP needs to be designed greater than Vout (with max ripple). You can try reducing Rvs2 resistor slightly to achieve this.

    Q2. There is no internal voltage clamp on the Vdd pin. You might need to add it externally and select zener clamp based on the Vdd voltage. The startup is governed by the following equation and is a function of (Rstr, Cdd, tstr, Istart)

    Please let us know if you have any questions.

    Thank you