1A Adjustable/Fixed Low Dropout Linear Regulator# Technical Documentation: FAN1117AT18 Low Dropout Voltage Regulator
Manufacturer : FAIRCHILD (ON Semiconductor)
Component : FAN1118AT18 (Fixed 1.8V Output LDO Regulator)
Document Version : 1.0
Date : October 2023
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## 1. Application Scenarios
### Typical Use Cases
The FAN1117AT18 is a 1.8V fixed-output, low dropout (LDO) linear voltage regulator designed for applications requiring stable, clean power from a higher input voltage. Its primary function is to provide precise voltage regulation with minimal dropout voltage, making it ideal for powering sensitive analog and digital circuits.
Primary Applications Include:
- Microcontroller/Microprocessor Power Rails : Providing clean 1.8V core voltage or I/O voltage to modern low-voltage processors, FPGAs, and ASICs that operate at this common logic level.
- Memory Module Power Supply : Suitable for DDR memory interfaces, flash memory, and other memory devices requiring a stable 1.8V supply.
- Sensor and Analog Front-Ends : Powering precision analog components such as operational amplifiers, ADCs, and sensors where noise on the power rail directly impacts measurement accuracy. The low output noise characteristic is critical here.
- Post-Regulation for Switching Supplies : Used as a secondary regulator following a noisier switching regulator (e.g., a buck converter) to achieve a very clean final output voltage, combining efficiency with precision.
- Portable/Battery-Powered Devices : Efficiently regulating voltage from a Li-ion battery (typically 3.7V nominal) or multiple NiMH cells down to 1.8V for system-on-chips (SoCs) and peripheral ICs.
### Industry Applications
- Consumer Electronics : Smartphones, tablets, digital cameras, set-top boxes, and IoT devices.
- Telecommunications & Networking : Routers, switches, modems, and RF modules where stable voltage for PLLs, VCOs, and SerDes interfaces is essential.
- Industrial Automation : PLCs, motor controllers, and measurement equipment.
- Automotive Infotainment & Body Electronics : Non-critical ECUs, display systems, and sensor modules (note: not typically qualified for under-hood/high-temperature automotive use unless specified).
- Medical Devices : Portable monitors and diagnostic equipment where reliable, low-noise power is mandatory.
### Practical Advantages and Limitations
Advantages:
- Low Dropout Voltage : Typically 1.1V at 800mA load, allowing operation with a small input-to-output differential. This maximizes efficiency and extends battery life in portable applications.
- High Accuracy : Fixed output voltage tolerance of typically ±1% (max ±2%) over line, load, and temperature variations.
- Integrated Protection : Features over-current protection (OCP) and thermal shutdown, enhancing system reliability.
- Low Output Noise : Excellent ripple rejection (typically 65dB at 120Hz), crucial for noise-sensitive analog and RF circuits.
- Simple Implementation : Requires only input and output capacitors for basic operation, simplifying design and reducing BOM cost.
Limitations:
- Linear Regulator Inefficiency : Power dissipation (P_diss = (V_in - V_out) * I_load) can be significant at high load currents or high input voltages, requiring thermal management (heatsinking).
- Fixed Output Voltage : The 'AT18' variant is fixed at 1.8V. For adjustable voltages, a different variant (e.g., FAN1117) is required.
- Maximum Current Limit : Rated for 1A output current, but practical continuous current may be lower depending on thermal conditions (junction temperature).
- Requires Stable Input : While it has good PSRR, performance degrades at high frequencies.
