In BF547, DO I need to feed the OTP with external 7v ,like in The bf51x family ? Or is it sufficient enternal 3.3v when writing to OTP ?
BF54x has on chip charge pump which is used to apply the voltage levels appropriate for programming the OTP memory. You need to ensure the appropriate VDDINT, VDDEXT and Tj for OTP programming.
Have a look at the Operating Conditions(Pg 34) section in the data sheet (please see the foot notes as well).
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