What is the efficiency of my LDO? Conversion efficiency is Vout/Vin expressed as a %. Why do some LDO datasheets state Tjmax as +150°C for some packages and +125°C for others? These are older datasheets – the +150°C is the max package/case may see, where +125°C is the maximum Tj. Why is my LDO not regulating properly? Many possible reasons: current limit has been activated, thermal shutdown has been exceeded, dropout voltage spec not obeyed, ESR of rules for the capacitors is not obeyed, etc.