## Overview of the LX1663ACN The **LX1663ACN** is a specialized Integrated Circuit (IC) manufactured by Microsemi (now part of Microchip Technology). It is primarily designed as a **Programmable Pulse Width Modulation (PWM) Controller** used for high-efficiency DC-DC conversion. This specific IC was popular in the late 90s and early 2000s for managing power in computer motherboards, specifically for providing the **Vcore voltage** to Pentium-class processors. --- ### Technical Specifications The following table outlines the key electrical characteristics of the LX1663ACN: | Feature | Specification | | :--- | :--- | | **Package Type** | 16-Pin Plastic DIP (Dual In-line Package) | | **Input Voltage ($V_{CC}$)** | 4.75V to 12V | | **Output Type** | Synchronous Buck PWM | | **Frequency Range** | 200 kHz to 400 kHz (Adjustable) | | **DAC Resolution** | 5-Bit (Provides 1.3V to 3.5V range) | | **Efficiency** | > 90% (Typical in optimized circuits) | --- ### Key Internal Components and Functions 1. **5-Bit Voltage ID (VID) DAC:** This is the "brain" of the chip. It reads a 5-bit binary code from the CPU and automatically sets the reference voltage. This allows the motherboard to support different CPUs with different voltage requirements without manual jumpers. 2. **Synchronous Rectifier Driver:** Unlike standard buck converters that use a diode, the LX1663ACN drives two N-channel MOSFETs. This "synchronous" approach significantly reduces heat and increases efficiency. 3. **Soft-Start Circuitry:** Prevents large inrush currents during startup, protecting the power supply and the sensitive microprocessor. 4. **Error Amplifier:** Constantly monitors the output voltage and compares it to the DAC reference, adjusting the PWM duty cycle in real-time to maintain stability. --- ### Typical Pin Configuration (16-Pin DIP) | Pin Number | Name | Description | | :--- | :--- | :--- | | 1-5 | VID0 - VID4 | Voltage Identification inputs from the CPU. | | 8 | GND | Ground reference. | | 11 | DRIVE L | Gate drive for the lower MOSFET. | | 12 | DRIVE H | Gate drive for the upper MOSFET. | | 14 | VCC | Supply voltage for the IC. | | 16 | SS | Soft-start capacitor connection. | --- ### Applications * **Legacy Motherboards:** VRM (Voltage Regulator Module) for Pentium II, Pentium III, and AMD K6 processors. * **Embedded Systems:** High-current step-down conversion for FPGA or DSP power rails. * **Industrial Controls:** Stable DC power supplies requiring programmable output levels.