The LT1123 is a 3-pin bipolar device designed to be used in conjunction with a discrete PNP power transistor to form an inexpensive low dropout regulator. The LT1123 consists of a trimmed bandgap reference, error amplifier, and a driver circuit capable of sinking up to 125mA from the base of the external PNP pass transistor. The LT1123 is designed to provide a fixed output voltage of 5V. The drive pin of the device can pull down to 2V at 125mA (1.4V at 10mA). This allows a resistor to be used to reduce the base drive available to the PNP and minimize the power dissipation in the LT1123. The drive current of the LT1123 is folded back as the feedback pin approaches ground to further limit the available drive current under short-circuit conditions. Total quiescent current for the LT1123 is only 700µA. The device is available in a low cost TO-92 package.
The LT1123 is a 3‑pin bipolar device intended for use with an external PNP pass transistor to form an inexpensive low‑dropout regulator. It provides a fixed 5 V output, 4 A output current capability, and features a trimmed bandgap reference, error amplifier, and driver circuit.
The datasheet includes absolute maximum ratings, electrical characteristics, typical performance curves, pin functions, application information, thermal considerations, and package dimensions, helping designers implement the regulator in various low‑dropout applications.
| Quiescent Current | 700 µA |
|---|---|
| Fixed Output Voltage | 5 V |
| Maximum Output Current | 4 A |
| Typical Dropout Voltage at 4 A | 0.75 V |
| Package Type | 3‑Lead Plastic TO‑92 |
The LT1123 draws a quiescent current of 700 µA.
The device can supply up to 4 A of output current.
It is available in a 3‑lead plastic TO‑92 package.
At 4 A output the typical dropout voltage is about 0.75 V.