ITU CO/PABX SLIC with Low Power Standby# Technical Documentation: HC5515CM Subscriber Line Interface Circuit (SLIC)
Manufacturer : HAR (Harris Corporation / Renesas Electronics lineage)
Component Type : Subscriber Line Interface Circuit (SLIC) with Ringing
Document Version : 1.0
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## 1. Application Scenarios
### 1.1 Typical Use Cases
The HC5515CM is a monolithic, high-voltage SLIC designed primarily for POTS (Plain Old Telephone Service) line interfaces. Its core function is to provide the necessary BORSCHT functions (Battery feed, Overvoltage protection, Ringing, Supervision, Coding, Hybrid, and Testing) between a digital telephony system (like a PBX, central office switch, or VoIP gateway) and an analog telephone line.
* Analog Telephone Line Termination: It serves as the physical interface for a single subscriber line, providing the -48V DC battery feed, detecting on-hook/off-hook status, and generating the 20 Hz AC ringing voltage (up to 70 Vrms).
* FXS (Foreign Exchange Station) Ports: In VoIP (Voice over IP) gateways, IP-PBXs, and analog terminal adapters (ATAs), the HC5515CM provides the standard analog interface to connect traditional telephones, fax machines, or modems to a digital/IP network.
* Key System and PBX Line Cards: It forms the fundamental building block for the line card of small to medium business telephone systems, handling the analog signaling for each extension.
### 1.2 Industry Applications
* Telecommunications Infrastructure: Legacy central office (CO) line cards and remote terminal units.
* Enterprise Communication: Digital and IP-based Private Branch Exchanges (PBX), voice mail systems.
* Customer Premises Equipment (CPE): Integrated Access Devices (IADs), VoIP residential gateways, security system dialers.
* Industrial and Utility Telemetry: Systems that utilize standard analog phone lines for remote data acquisition and control signaling.
### 1.3 Practical Advantages and Limitations
Advantages:
* High Integration: Combines battery feed, ringing, and supervision functions in a single 24-pin package, reducing board space and component count compared to discrete designs.
* Programmable Ringing: Ringing amplitude and frequency can be controlled via external resistors, offering design flexibility.
* Built-in Protection: Features on-chip thermal shutdown and current limiting, enhancing system reliability.
* Low Power Standby: Efficient power management in on-hook (idle) state.
* Proven Technology: Based on a mature, well-understood architecture with extensive field history.
Limitations:
* Legacy Technology: Primarily designed for traditional telephony. Lacks native support for advanced features like wideband audio (HD Voice) or integrated codecs, which require external components.
* External Components Required: Still needs a significant number of external passive components (resistors, capacitors, transformers, protection devices) for a complete solution.
* High-Voltage Management: Requires careful handling of high-voltage rails (e.g., -48V, high-voltage ringing) for both safety and performance.
* Heat Dissipation: During ringing and off-hook states, power dissipation can be significant, necessitating proper thermal design, often requiring a heatsink on the package.
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## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
* Pitfall 1: Inadequate Ringing Voltage/Current. Attempting to drive multiple phones or long loops with insufficient ringing amplitude or current capability.
* Solution: Calculate total REN (Ringer Equivalence Number) of connected devices and loop resistance. Ensure the high-voltage ringing supply (`VRING`)
