What is the difference between the “A” and “non-A” versions of LT1963/A, LT1764/A? The “A” version is a newer, pin compatible design that is stable with very low ESR capacitors such as ceramic caps, in addition to tantalum and electrolytic. What is current limit foldback? This is current limiting technique to limit the peak power dissipation in the power transistor to prevent thermal destabilization or thermal runaway by keeping the transistor in its SOA (safe operating area).