LP2985AIM5-3.3 Linear Regulator: Working Principle, Pinout and Package

Post Date: 2025-06-30

LP2985AIM5-3.3 Introduction

The LP2985AIM5-3.3 is a low noise, low dropout (LDO) linear regulator with a maximum output current of 150mA and requires only a 300mV voltage difference between input and output for stable operation. It is designed using VIP processes (vertically integrated PNP) and is particularly suitable for battery-powered applications.

LP2985AIM5-3.3 Working Principle

The primary function of the LP2985AIM5-3.3 is to regulate an unstable input voltage (VIN) into a fixed 3.3V output (VOUT), even when the input is only slightly higher than 3.3V. Internally, the chip integrates a high-precision 1.23V reference voltage, an error amplifier, a PNP power transistor, and overcurrent/overtemperature protection circuits.

When voltage is applied to the input, the output voltage is compared—via a resistor divider—to the reference voltage. Based on the comparison, the error amplifier adjusts the conduction of the internal power transistor, ensuring a stable and consistent output voltage.

LP2985AIM5-3.3 Pinout

IN: Input voltage

GND: Common ground (device substrate)

ON/OFF: Logic high enable input

BYPASS: Bypass capacitor for low noise operation

OUT: Regulated output voltage

LP2985AIM5-3.3 Symbol

LP2985AIM5-3.3 3D Model

LP2985AIM5-3.3 Specification

Parameter	Value
Output Voltage (VOUT)	3.3 V (Fixed)
Input Voltage	16V
Output Current (IOUT)	150 mA
Dropout Voltage	0.58V @ 150mA
Quiescent Current (IQ)	95 µA
Supply Current	2.5 mA
PSRR	45dB (1kHz)
Output Voltage Accuracy	±1%
Recommended CBYPASS	0.01 µF
Operating Temperature	-40°C ~ 125°C
Package Type	SOT-23-5

LP2985AIM5-3.3 Features

Input Voltage Range: 2.5 V to 16 V

Ultra Low-Dropout Voltage

Ensured 150 mA Output Current

Requires Minimum External Components

Stable With Low-ESR Output Capacitor

< 1 μA Quiescent Current When Shut Down

Low Ground Pin Current at All Loads

Output Voltage Accuracy 1% (A Grade)

High Peak Current Capability

Low ZOUT: 0.3 Ω Typical (10 Hz to 1 MHz)

Overtemperature and Overcurrent Protection

−40°C to 125°C Junction Temperature Range

Custom Voltages Available

LP2985AIM5-3.3 Applications

Cellular Phones

Palmtop and Laptop Computers

Personal Digital Assistants (PDA)

Camcorders, Personal Stereos, Cameras

LP2985AIM5-3.3 Simplified Schematic

This simplified schematic shows the basic application of the LP2985AIM5-3.3 low-dropout (LDO) voltage regulator. The IN pin receives the input voltage (VIN), which is filtered by a 1 µF input capacitor (CIN) to ensure stable operation and reduce noise. The OUT pin provides the regulated output voltage (VOUT), stabilized by a 2.2 µF output capacitor (COUT) to maintain voltage accuracy and minimize output ripple. The GND pin connects to ground.

The ON/OFF pin enables or disables the regulator; pulling it high turns the regulator on, while pulling it low shuts it off. The BYPASS pin is connected to a 0.01 µF capacitor (CBYPASS), which improves noise performance by filtering the internal reference, reducing output noise to very low levels.

LP2985AIM5-3.3 Functional Block Diagram

This block diagram illustrates the internal structure of the LP2985AIM5-3.3, a low-dropout (LDO) linear regulator. The input voltage (IN) is regulated by a pass transistor controlled by an internal error amplifier.

The amplifier compares the output voltage to an internal reference voltage (VREF = 1.23 V) and adjusts the gate of the transistor accordingly to maintain a stable VOUT. A resistor divider network samples the output voltage for feedback into the error amplifier.

The circuit also includes on/off control logic, allowing the regulator to be enabled or shut down via the ON/OFF pin. The BYPASS pin is connected to the reference block, allowing a capacitor to reduce output noise.

LP2985AIM5-3.3 Package

The SOT-23-5 is a compact surface-mount package commonly used for low-power integrated circuits. It features five terminals and offers a small footprint, making it ideal for space-constrained applications such as portable and battery-powered devices.