KSZ8721BLI - 3.3V 10/100 Ethernet PHY | Microchip
MPN: KSZ8721BLI ✓ ActiveKSZ8721BLI Overview
An Ethernet physical-layer transceiver, or Ethernet PHY, converts digital frame data into electrical or optical signaling suitable for a network medium. In the hierarchy of network semiconductors, the PHY sits below the Ethernet controller or media-access controller and above the transformer, connector, or fiber interface. The KSZ8721BLI also provides an MDI/MDI-X auto-crossover function, allowing copper links to use a standard straight-through cable arrangement without manual crossover configuration.
The KSZ8721BLI combines 10BASE-T and 100BASE-TX/FX support in one transceiver while offering both MII and RMII host connectivity. Full MII provides a parallel interface for legacy or higher-bandwidth controller arrangements, whereas RMII reduces the number of host-side signals and is useful in space-constrained embedded systems. The single 3.3 V supply architecture simplifies power design, although interface voltage compatibility must still be checked against the selected host controller.
The device is positioned for industrial embedded networking, where a 10/100 Mbps copper or fiber link can be added without implementing the complete Ethernet data path in the host. Its industrial temperature option is identified by the KSZ8721 family documentation, which lists a -40°C to +85°C industrial range. Package construction is surface-mount LQFP, allowing conventional PCB assembly and inspection while requiring careful pin-1 orientation and solderability checks.
Typical uses include industrial controllers, factory automation equipment, embedded gateways, serial-to-Ethernet systems, media converters, and compact network appliances. For copper links, designers must add the appropriate isolation transformer and RJ-05 or shielded-jack hardware. For fiber links, the external optical components and interface requirements should be implemented according to the manufacturer application guidance rather than inferred from the PHY package alone.
The main design consideration is interface verification. Confirm that the host controller supports the selected MII or RMII mode, the transceiver’s supply voltage, and the external magnetics required by the target copper or fiber network. This page consolidates the verified source links, pricing observation, package information, replacement data, and engineering considerations into a practical procurement and design reference.
Drop-in alternatives for KSZ8721BLI — 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 KSZ8721BLI (same form factor and footprint) — differing in Package, Product Type, Supply Voltage, Data Rate.
KSZ8721BL
✅ Drop-InContact for price
View Datasheet →KS8721BL
✅ Drop-In📋 Reference alternative (not in catalog)
KSZ8721BLI Specifications
| Product Type | 10/100BASE-TX/FX Ethernet physical-layer transceiver |
| Supply Voltage | 3.3 V |
| Operating Voltage Range | 2.5 V to 3.3 V |
| Data Rate | 10 Mbps and 100 Mbps |
| Copper Media Support | 10BASE-T and 100BASE-TX |
| Fiber Media Support | 100BASE-FX |
| Host Interface | MII and RMII |
| Number of Transceivers | 1 |
| Ethernet Standards | IEEE 802.3 and IEEE 802.3u |
| Auto Crossover | MDI/MDI-X auto-crossover |
| Package | 48-LQFP, 7 x 7 mm |
| Pin Count | 48 pins |
| Mounting Type | Surface mount |
| Industrial Temperature Range | -40°C to +85°C |
| RoHS Status | Compliant |
| Observed Unit Price | $2.5389 as of 2026-10-30 |
| Distributor Availability | In stock at LCSC as of 2026-10-30 |
KSZ8721BLI 48-lqfp, 7 x 7 mm Pin Configuration Guide
Pin configuration for KSZ8721BLI (48-lqfp, 7 x 7 mm 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 KSZ8721BLI.
Refer to the datasheet for full pin configuration.
Typical Applications
KSZ8721BLI is suitable for 6 applications: Industrial Ethernet Controllers, Factory Automation Gateways, Serial-to-Ethernet Converters, 100BASE-FX Media Converters, Embedded Network Appliances, Renovation and Building Controls.
Industrial Ethernet Controllers
The KSZ8721BLI fits industrial embedded controllers that need a 10/100 Mbps copper link while operating from a 2.5 V to 3.3 V supply. According to the Microchip product page, the transceiver supports 10BASE-T and 100BASE-TX and offers both MII and RMII host interfaces. It can be placed beside a network controller, with MDI/MDI-X auto-crossover simplifying direct copper connections. The BLI industrial designation supports operation from -40°C to +85°C. Designers should still add qualified isolation magnetics and surge protection, and should verify the host interface voltage and reset timing against the selected controller.
Recommended
Factory Automation Gateways
The KSZ8721BLI is useful in factory gateways that bridge serial, sensor, or controller data to a 10/100 Mbps Ethernet network. Its 48-LQFP 7 x 7 mm package avoids the larger footprint associated with many older multi-interface PHYs, while the 3.3 V single-supply operation supports compact controller boards. MDI/MDI-X auto-crossover allows the gateway to work with standard copper cabling without manual TX/RX crossover wiring. For industrial deployment, design the magnetics and RJ interface for isolation, conducted-noise resilience, and the required industrial temperature range.
Recommended
Serial-to-Ethernet Converters
The KSZ8721BLI can provide the Ethernet physical layer in a serial-to-Ethernet converter because it supports both 10BASE-T and 100BASE-TX at 10 Mbps and 100 Mbps. Its RMII interface reduces the number of host-controller connections when RMII is available, while full MII supports controller arrangements that require the wider parallel interface. A complete design still needs a network controller, isolation transformer, RJ-05 jack or shielded connector, and a magnetics-compatible physical layout. The observed $2.5389 price as of 2026-10-30 supports cost-sensitive embedded networking projects.
Recommended
100BASE-FX Media Converters
The KSZ8721BLI is appropriate for compact 100BASE-FX media-converter and fiber-interface designs because the verified description identifies support for 100BASE-FX alongside 10BASE-T and 100BASE-TX. Its MII and RMII host interfaces let a system controller coordinate copper and fiber media functions. The PHY is only one part of a fiber design; the implementation must also use suitable optical drivers, receivers, optical-device power, and connectorization. Validate loss budget, optical wavelength, launch power, and receiver sensitivity through the complete optical design rather than relying on the Ethernet data rate alone.
Recommended
Embedded Network Appliances
The KSZ8721BLI suits compact embedded appliances requiring an economical wired-network connection. Its 48-LQFP 7 x 7 mm package provides a manageable surface-mount footprint, and its 2.5 V to 3.3 V operating range can support low-power host platforms. The MDI/MDI-X auto-crossover function improves installation flexibility in consumer and commercial equipment. Keep the PHY, magnetics, and connector in a controlled copper-media region, provide suitable decoupling, and avoid long uncontrolled copper traces that can degrade signal integrity or increase susceptibility to external interference.
Recommended
Renovation and Building Controls
The KSZ8721BLI can be used in low-cost building-control and room-controller nodes that need wired 10/100 Mbps connectivity. The -40°C to +85°C industrial-temperature option is relevant to equipment installed outside conditioned spaces, while auto-crossover improves compatibility with existing building-network cabling. A practical design should include isolation magnetics, surge protection, and an appropriate connector or terminal arrangement. The host controller can use RMII to reduce wiring when the platform supports it, or MII when the controller implementation requires the full parallel interface.
Recommended
Recommended Products Summary
Engineering reference data for KSZ8721BLI — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | KSZ8721BL | KS8721BL |
|---|---|---|---|
| Package | 48-LQFP (7x7) | 48-LQFP (7x7) | 48-LQFP (7x7) |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology |
| Product Type | 10/100BASE-TX/FX Ethernet PHY | 10/100BASE-TX/FX Ethernet PHY | Related 10/100 Ethernet physical-layer family |
Key Differentiators
- Combines copper and fiber physical layers with two host-interface choices (vs KS8721BL)
- Documented same-board replacement path (vs KSZ8721BL)
- Industrial temperature ordering option (vs KS8721BL)
Design Notes
Place the KSZ8721BLI, isolation magnetics, and network connector in the same controlled Ethernet signal region. Keep copper traces between the PHY and magnetics short, provide the required return-path geometry, and follow the manufacturer reference layout. Decoupling capacitors should be placed directly beside their associated supply pins, while high-speed or isolation-related components should not be separated by unrelated circuitry.
Do not assume that the BLI ordering suffix can be replaced solely because another KSZ8721 variant uses the same family name. Confirm the package drawing, temperature grade, supply requirements, host-interface mode, and ordering table. The supplied evidence supports KSZ8721BL as a strong replacement candidate, but production approval should include comparison of the manufacturer datasheet and a review of any firmware or device-strapping changes.
Use qualified Ethernet isolation magnetics and a shielded or filtered network connector to reduce radiated and conducted emissions. Copper interfaces are especially sensitive to externally coupled transients, so include the protection strategy appropriate to the installation. For fiber operation, keep the optical interface and PHY electronics arranged so that high-current switching paths do not share sensitive return paths with the 2.5 V to 3.3 V circuitry.
Verify the transceiver’s supply rails against the host controller before committing to the board. The verified product data identifies a 2.5 V to 3.3 V operating range, but logic-level compatibility, startup order, and exposed-pad requirements must be taken from the exact datasheet. Use local bulk and high-frequency decoupling, provide adequate return-current paths, and avoid relying on long supply traces to create filtering.
Compliance Information
RoHS compliance was reported by the supplied component-index record. The other compliance fields were not established by the verified sources and remain unknown.
