Two Phase Interleaved Synchronous Buck Converter for AMD Hammer# Technical Documentation: FAN5098MTC Synchronous Buck Controller
Manufacturer : FAIRCHILD (now part of ON Semiconductor)
Component : FAN5098MTC – Multiphase Synchronous Buck PWM Controller
Package : 28-Lead TSSOP (TMC)
Classification : High-Performance, Multiphase DC-DC Controller
---
## 1. Application Scenarios
### Typical Use Cases
The FAN5098MTC is a dual-phase, synchronous buck PWM controller designed to drive two out-of-phase power stages. Its primary use case is in generating tightly regulated, high-current, low-voltage power rails from a higher input voltage source. A classic implementation involves converting a 12V input bus to a 1.0V to 1.8V output capable of delivering 30A to 60A or more, depending on the external MOSFET and inductor selection.
A standard application circuit consists of the FAN5098MTC, two sets of N-channel high-side and low-side MOSFETs, two power inductors, input/output capacitors, and a current-sense network. The controller interleaves the two phases 180° apart, significantly reducing input ripple current and allowing the use of smaller, lower-cost input capacitors.
### Industry Applications
1. High-Performance Computing:
* Central Processing Unit (CPU) Core Voltage (VCORE) Regulators: In servers, workstations, and high-end desktop motherboards, the FAN5098MTC is ideal for generating the high-current, low-voltage (e.g., 1.2V @ 80A) rail required by modern multi-core processors. Its multiphase architecture is essential for meeting transient response requirements.
* Graphics Processing Unit (GPU) Power: Used on graphics cards to provide the primary power rail for the GPU core.
* Memory Termination (VTT) and Chipset Power: For DDR memory systems and platform controller hubs.
2. Telecommunications & Networking Equipment:
* Powers ASICs, FPGAs, and network processors in routers, switches, and base stations where high efficiency and reliability are critical.
3. Industrial Systems:
* Provides the main logic supply for PLCs, motor drives, and test/measurement equipment that utilize high-performance digital ICs.
### Practical Advantages and Limitations
Advantages:
* High Efficiency: Synchronous rectification and multiphase operation minimize conduction and switching losses, especially at high load currents. Efficiency often exceeds 90% across a wide load range.
* Excellent Transient Response: The dual-phase architecture inherently doubles the effective switching frequency for the output capacitor, allowing it to respond rapidly to sudden load steps (e.g., when a CPU changes power states).
* Reduced Input Ripple: Interleaving cancels a significant portion of the input current ripple, easing EMI filter design and reducing stress on the input source.
* Integrated Features: Includes over-voltage protection (OVP), under-voltage lockout (UVLO), and programmable over-current protection (OCP) using external sense resistors, enhancing system robustness.
* Voltage Positioning (Droop): Programmable active voltage positioning improves transient performance while optimizing output capacitor requirements.
Limitations:
* Design Complexity: A multiphase buck converter is significantly more complex to design, lay out, and tune than a single-phase solution. It requires careful matching of components between phases.
* Component Count: Requires two complete sets of power components (MOSFETs, inductors, gate drivers), increasing board area and BOM cost.
* Control Loop Compensation: Tuning the feedback loop for stability across all load conditions requires expertise and careful measurement.
* Limited to
