The TC57 is a low dropout regulator controller that operates with an external PNP pass transistor, allowing the user to tailor the LDO characteristics to suit the application at hand. This results in lower dropout operation (and often lower cost) compared with traditional linear regulators with on-board pass transistors. The maximum output current of a TC57based regulator circuit is limited only by the characteristics of the external pass transistor. For example, a maximum output current of 650mA (with a dropout voltage of 100mV) results when an FZT749 pass transistor is used, while a Darlington configuration can deliver up to 4A.