KSZ8721B - 2.5V 10/100 Ethernet PHY | Microchip
MPN: KSZ8721B ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $5.4078 | $5.41 |
| 10 | $5.4078 | $54.08 |
| 100 | $5.4078 | $540.78 |
| 500 | $5.4078 | $2,703.90 |
| 1,000 | $5.4078 | $5,407.80 |
KSZ8721B Overview
An Ethernet physical-layer transceiver, or Ethernet PHY, converts digital frame data into signals suitable for copper twisted-pair or fiber media and converts received signals back into digital data. The KSZ8721B belongs to the Ethernet interface hierarchy: transceiver -> physical layer -> network interface IC -> semiconductor. Its 2.5 V operating supply is suitable for low-power embedded platforms that already provide compatible I/O levels.
The KSZ8721B supports 10Base-T and 100Base-TX operation, along with 100Base-FX capability as identified in the product description. The MII and RMII host interfaces support different host-side connection styles, allowing the same PHY to serve systems with parallel media-independent or reduced media-independent interfaces. The device also includes integrated 10Base-T functions, reducing the need for separate medium-access and coding functions around the PHY.
The verified product listing describes KSZ8721B as a 48-SSOP part and identifies it as a 10/100 Base-TX/FX MII physical-layer transceiver. The manufacturer’s related datasheet snippet identifies the KS8721B/BT family as operating at 2.5 V and containing PMA, PMD, and PCS functions. Electrical limits, exact pin functions, temperature limits, clocking requirements, and layout guidance should be taken from the manufacturer datasheet before final design release.
Typical uses include industrial Ethernet controllers, embedded control systems, communication modules, test equipment, and low-power network appliances. The MII interface is useful when the host controller requires a conventional parallel bus, while RMII can reduce the number of host-side signals in compatible designs. The 2.5 V supply also helps system designers manage power budgets on compact embedded boards.
When laying out the circuit, place the PHY, magnetics, connector, decoupling, and clock or reset components according to the manufacturer reference layout. Validate signal integrity across MII or RMII timing, provide continuous reference planes, and verify cable and magnetics compatibility. The KSZ8721B is not a general-purpose connector or power device, so its SOA field is not applicable.
This page consolidates the verified manufacturer and distributor information for the KSZ8721B, including package identity, interface type, sourcing links, practical application guidance, and clearly marked data gaps. It is intended to accelerate engineering evaluation while avoiding unsupported electrical claims.
Drop-in alternatives for KSZ8721B — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with KSZ8721B (same form factor and footprint) — differing in Package.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
KS8721B
✅ Drop-In📋 Reference alternative (not in catalog)
KS8721B-BT
✅ Drop-In📋 Reference alternative (not in catalog)
KSZ8721SL
✅ Drop-In📋 Reference alternative (not in catalog)
KSZ8721BL
✅ Drop-In✓ In Stock
Contact for price
View Datasheet →KSZ8721B Specifications
| Device Type | 10/100 BASE-TX/FX MII physical-layer transceiver |
| Operating Supply Voltage | 2.5 V |
| Ethernet Speeds | 10Base-T and 100Base-TX |
| Fiber Capability | 100Base-FX |
| Host Interface | MII and RMII |
| Physical Layer Functions | 10BaseT PMA, PMD, and PCS functions |
| Supply Architecture | Single-supply operation |
| Package | 48-SSOP |
| Mounting Type | Surface mount |
| Component Type | Semiconductor |
| RoHS Status | unknown |
| REACH Status | unknown |
| Automotive AEC-Q100 Status | unknown |
KSZ8721B 48-ssop Pin Configuration Guide
Pin configuration for KSZ8721B (48-ssop package). Pin numbering, functions, and connection diagrams are defined in the manufacturer datasheet. Refer to it for the exact footprint and soldering guidelines.
No detailed pinout data available for KSZ8721B.
Refer to the datasheet for full pin configuration.
Typical Applications
KSZ8721B is suitable for 6 applications: Industrial Ethernet Controller, Embedded Network Communication Module, Test and Measurement Ethernet Port, Low-Power Embedded Device, Fiber-Ready Remote Sensor Gateway, Automotive or Mobile Network Interface.
Industrial Ethernet Controller
The KSZ8721B fits an industrial Ethernet controller that connects embedded processing to a 10/100 copper network. Its 2.5 V operating supply and MII/RMII host options let the designer match the PHY to the controller’s bus architecture instead of forcing a common interface. Place the PHY near the Ethernet magnetics and connector, keep the host-side lines short, and validate timing against the selected MII or RMII specification. The main performance consideration is signal integrity: a 48-SSOP device can support compact designs, but connector return paths, impedance-controlled routing, and magnetics layout remain critical.
Recommended
Embedded Network Communication Module
For a compact embedded communication module, KSZ8721B provides the physical-layer endpoint for a controller running TCP/IP or UDP traffic. Its 10Base-T and 100Base-TX support allows deployment across common copper Ethernet networks, while 100Base-FX capability can extend the design toward fiber media. The circuit should reserve space for compatible magnetics, provide clean 2.5 V regulation, and route RMII or MII signals according to the host timing budget. Designers should verify media distance, connector selection, and thermal performance across the complete enclosure.
Recommended
Test and Measurement Ethernet Port
The KSZ8721B can serve as the Ethernet PHY in test equipment that exposes measurements, configuration data, or status over a 10/100 network. MII support is useful with controllers designed around a parallel media-independent interface, while RMII can simplify host-side pin count in compatible designs. Keep the PHY-to-magnetics path compact and maintain continuous ground references to reduce susceptibility to external test fixtures and switching supplies. Before production, confirm the exact timing, reset, clock, and power requirements from the manufacturer datasheet.
Recommended
Low-Power Embedded Device
KSZ8721B is appropriate for embedded platforms where a 2.5 V PHY rail is available and low-voltage operation simplifies power management. The device provides 10Base-T and 100Base-TX connectivity without requiring the designer to implement separate PMA, PMD, and PCS functions in the host. Use RMII when the host controller supports it and MII when timing or legacy architecture favors it. The power benefit depends on the complete system load, external magnetics, regulator efficiency, and Ethernet activity, so measure the assembled design rather than assuming the nominal PHY supply alone determines system consumption.
Recommended
Fiber-Ready Remote Sensor Gateway
The 100Base-FX capability identified for KSZ8721B can support remote sensor gateways where copper reach is insufficient or electrical isolation is desirable. The PHY handles the Ethernet physical layer, while a host processor and protocol stack determine application behavior. The fiber implementation requires appropriate fiber magnetics or optical components, controlled differential routing, and a power design that meets the selected media’s startup and steady-state requirements. Treat fiber capability as a design direction rather than a complete optical solution; the exact supported optical configuration and timing must come from the official datasheet.
Recommended
Automotive or Mobile Network Interface
KSZ8721B may be considered for non-harsh embedded network interfaces, but automotive suitability cannot be assumed from the supplied data. Its 2.5 V operation, 10/100Base-TX support, and MII/RMII flexibility are useful for a compact communication subsystem, while 100Base-FX can support longer or isolated links. Before using it in a vehicle or mobile product, verify temperature range, EMC performance, vibration constraints, lifecycle commitments, and any required automotive qualification directly with Microchip. Do not infer AEC-Q100 status from the product family name.
Recommended
Recommended Products Summary
Engineering reference data for KSZ8721B — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | KS8721B | KS8721B-BT | KSZ8721SL | KSZ8721BL |
|---|---|---|---|---|---|
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
Key Differentiators
- MII and RMII host-interface flexibility (vs KS8721B)
- Integrated physical-layer functions (vs KS8721B)
- 2.5 V operating supply (vs KS8721B)
Design Notes
Use the manufacturer’s KSZ8721B reference layout as the starting point for the 48-SSOP footprint, Ethernet magnetics, connector, and decoupling network. Keep the PHY-to-magnetics path compact, route differential pairs over continuous reference planes, and avoid placing high-current switching paths beneath sensitive receive traces. Confirm land pattern, exposed-pad or lead details, and component-side orientation against the actual package drawing before release.
MII and RMII signals are timing-sensitive host interfaces. Match trace topology and impedance according to the manufacturer’s interface requirements, provide a clean clock or reset implementation where required, and keep external connector or magnetics return paths close to the signal pairs. Validate rise time, settling, and eye behavior with the selected host controller rather than relying only on nominal logic-level specifications.
The verified 2.5 V supply is a key constraint for system power design. Provide a low-noise regulator with adequate transient response, place decoupling capacitors close to the PHY supply pins, and verify the regulator’s startup and load behavior across Ethernet operating states. Exact current consumption and recommended capacitor values are not present in the supplied data, so calculate them from the official datasheet and the complete Ethernet subsystem.
Do not treat KSZ8721B as a complete Ethernet controller: a host MAC, processor interface, protocol stack, magnetics, and connector are still required. Also do not assume that a related KS8721 or KSZ8721SL/BL variant is a drop-in replacement solely because it has a similar name. Compare pin names, supply sequencing, timing, package dimensions, and media support using the manufacturer datasheets before substitution.
Compliance Information
The supplied verified data does not provide RoHS, REACH, lead-free, halogen-free, conflict-minerals, or automotive-qualification statements. Compliance must be confirmed from the current Microchip product documentation and the selected distributor record.
