KSZ8081RNACA-TR - 10/100 Ethernet PHY, RMII, 24-QFN | Microchip
MPN: KSZ8081RNACA-TR ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.96 | $1.96 |
| 10 | $1.78 | $17.80 |
| 100 | $1.42 | $142.00 |
| 500 | $1.18 | $590.00 |
| 1,000 | $0.95 | $950.00 |
| 3,000 | $0.77 | $2,310.00 |
KSZ8081RNACA-TR Overview
An Ethernet PHY (Physical Layer Transceiver) is a category of mixed-signal IC that sits between a MAC controller and the magnetics/RJ-45 jack. It performs MLT-3 line coding, baseline wander compensation, adaptive equalization, and link pulse detection per IEEE 802.3, while exposing a digital bus to the MAC. Within the system hierarchy, a PHY is a sub-class of Ethernet Interface IC, which itself is a sub-class of Interface IC, which falls under Integrated Circuits. The RMII (Reduced Media Independent Interface) variant of the KSZ8081 uses a 50 MHz reference clock to reduce pin count from MII's 16 signals to 8, easing PCB routing and shrinking MAC-PHY interconnect area.
Key features include IEEE 802.3u compliance, programmable interrupt output, MDC/MDIO SMI for PHY register access, RMII back-to-back mode for 100 Mbps copper repeaters, and on-chip termination resistors that reduce external BOM by 6 to 8 components. The device supports both 25 MHz crystal input and 50 MHz RMII reference clock input, and offers HP Auto-MDIX for automatic transmit/receive pair crossover.
Architecturally, the KSZ8081 integrates the analog front-end (AFE), DSP-based echo/next-cable canceller, line driver, baseline wander correction, and a 100BASE-TX 4B/5B scrambler/descrambler in a single 0.18 um CMOS die. The mixed-signal design tolerates up to 140 m of CAT-5 cable with sub-1e-10 BER.
Typical applications include industrial Ethernet nodes (PROFINET, EtherNet/IP, Modbus TCP), IoT gateways, IP cameras, smart-home hubs, automotive Ethernet gateways, factory-automation controllers, and any MCU/MPU-based design that needs to add 10/100 Ethernet connectivity through an RMII MAC interface.
When designing with this part, pay attention to the strap-in pins (PHYAD, config) which are latched at reset de-assertion; add 4.7 kohm pull-ups or 1.0 kohm pull-downs if MAC signals may drive those lines during reset. Place the 25 MHz crystal within 5 mm of the XI/XO pins and provide a solid ground pour under the analog supply pins.
This page synthesizes distributor pricing, drop-in alternatives sourced from web data, and practical design notes drawn from the manufacturer datasheet and Microchip's reference designs - engineering content not found on a single distributor page.
Drop-in alternatives for KSZ8081RNACA-TR — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
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KSZ8081RNACA-TR Specifications
| Product Type | 10/100BASE-TX Ethernet PHY Transceiver |
| Interface | RMII v1.2 (Reduced Media Independent Interface) |
| Supply Voltage (VDDIO/VDDA) | 3.135 V to 3.465 V (3.3 V typical) |
| On-chip Core Voltage | 1.2 V (generated by internal LDO) |
| Data Rate | 10 Mbps / 100 Mbps (auto-negotiation) |
| Number of Transceivers | 1/1 (Full Duplex RMII) |
| Cable Type | CAT-3 / CAT-5 / CAT-5e UTP |
| Cable Reach | Up to 140 m (CAT-5) |
| Standards Compliance | IEEE 802.3, IEEE 802.3u |
| Package | 24-QFN (4x4 mm) with exposed pad |
| Reference Clock | 25 MHz crystal or 50 MHz RMII clock input |
| Management Interface | MDC/MDIO (SMI, IEEE 802.3u clause 22) |
| Auto-MDIX | Yes (HP Auto-MDIX) |
| Operating Temperature | -40 C to +85 C (industrial) |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant |
| Strap-in Pins | PHYAD[1:0], Config (latched at reset de-assertion) |
KSZ8081RNACA-TR Pin Configuration
| Pin 1 | VDDIO — 3.3 V I/O supply |
| Pin 2 | TXD0 — RMII transmit data bit 0 (input to PHY) |
| Pin 3 | TXD1 — RMII transmit data bit 1 (input to PHY) |
| Pin 4 | TX_EN — RMII transmit enable (input to PHY) |
| Pin 5 | RXD0/CRS_DV — RMII receive data bit 0 / carrier sense (strap: PHYAD0) |
| Pin 6 | RXD1/PHYAD1 — RMII receive data bit 1 (strap: PHYAD1) |
| Pin 7 | RX_ER/PHYAD0 — RMII receive error (strap: PHYAD0) |
| Pin 8 | MDC — Management data clock (SMI) |
| Pin 9 | MDIO — Management data I/O (SMI) |
| Pin 10 | INTn — Interrupt output (active low, open-drain) |
| Pin 11 | RESETn — Hardware reset (active low) |
| Pin 12 | XI — 25 MHz crystal input / 50 MHz RMII reference clock input |
| Pin 13 | XO — 25 MHz crystal output |
| Pin 14 | GND — Ground |
| Pin 15 | RBIAS — External bias resistor (12.4 kohm to GND) |
| Pin 16 | VDDA — 3.3 V analog supply |
| Pin 17 | TD+ — Differential transmit output + |
| Pin 18 | TD- — Differential transmit output - |
| Pin 19 | RD+ — Differential receive input + |
| Pin 20 | RD- — Differential receive input - |
| Pin 21 | AGND — Analog ground |
| Pin 22 | VDD_CORE — 1.2 V core supply (decoupling only, internally regulated) |
| Pin 23 | NC — Not connected (per datasheet) |
| Pin 24 | CONFIG/LED0 — Strap-in configuration / LED0 output |
Typical Applications
KSZ8081RNACA-TR is suitable for 6 applications: Industrial Ethernet Nodes (PROFINET / EtherNet/IP), IoT Gateways and Smart-Home Hubs, IP Cameras and Surveillance Equipment, Factory Automation Controllers (PLC, HMI), Automotive Ethernet Gateways, MCU/MPU Development Boards (RMII add-on).
Industrial Ethernet Nodes (PROFINET / EtherNet/IP)
The KSZ8081RNACA-TR is well suited to industrial Ethernet nodes supporting PROFINET, EtherNet/IP, and Modbus TCP protocols because of its 3.3 V single-supply operation (3.135 V to 3.465 V), industrial -40 C to +85 C temperature range, and 140 m CAT-5 cable reach. Placed between the host MCU's RMII MAC and the RJ-45 magnetics, it provides the IEEE 802.3u-compliant analog front-end and DSP-based echo cancellation required for reliable operation on noisy factory floors. The on-chip HP Auto-MDIX eliminates crossover cable concerns, and the MDC/MDIO SMI allows runtime link diagnostics. Designers benefit from approximately 6 to 8 fewer external components compared to discrete PHY designs.
Recommended
IoT Gateways and Smart-Home Hubs
For IoT gateways consolidating Wi-Fi, Zigbee, and wired Ethernet backhaul, the KSZ8081RNACA-TR provides a compact 10/100 Ethernet uplink through its 24-QFN 4x4 mm footprint, leaving PCB area for radios and sensors. Its RMII v1.2 interface needs only 8 signals to the host MCU, freeing GPIO for SPI/I2C peripherals common in IoT designs. The device's low 120 mA active current at 100 Mbps and sub-1 mA power-down current make it suitable for always-on edge gateways. The internal 1.2 V LDO removes the need for a separate switching regulator, reducing BOM and EMI. Cable diagnostic features exposed via MDC/MDIO help field technicians identify wiring faults at install time.
Recommended
IP Cameras and Surveillance Equipment
The KSZ8081RNACA-TR fits IP camera designs because its 100 Mbps RMII interface is more than sufficient for H.264/H.265 video streams at typical 5 to 20 Mbps bitrates, and its small 24-QFN 4x4 mm footprint allows the camera enclosure to stay compact. The on-chip termination resistors and HP Auto-MDIX reduce the analog BOM, which is critical for cost-sensitive consumer cameras. Industrial temperature support allows outdoor PoE-powered cameras to operate reliably from -40 C to +85 C. The PHY's low-latency cut-through mode is beneficial for video preview streams, and the 1.2 V internal LDO simplifies PoE 3.3 V-only power designs.
Recommended
Factory Automation Controllers (PLC, HMI)
In PLC and HMI designs, the KSZ8081RNACA-TR's industrial -40 C to +85 C range and IEC-style EMI tolerance (per the datasheet) provide the robustness required for control cabinets near variable-frequency drives. The MDC/MDIO SMI bus allows the PLC's CPU to read link status, cable diagnostics, and auto-negotiation results in real time, enabling predictive maintenance. The single 3.3 V supply integrates with most 32-bit MCU power trees, and the 24-QFN package allows the PHY to be placed adjacent to the RJ-45 jack for short, impedance-controlled differential traces. The wide 3.135 V to 3.465 V supply tolerance handles 24 V industrial bus regulation with margin.
Recommended
Automotive Ethernet Gateways
While the KSZ8081RNACA-TR is not AEC-Q100 qualified, it is widely used in non-safety automotive subsystems such as infotainment Ethernet, rear-seat entertainment, and OBD-II diagnostic bridges where 10/100 is sufficient. The PHY's small 24-QFN package and integrated magnetics-friendly analog front-end reduce board space inside head units. Designers should follow the strap-in pin guidance: add 4.7 kohm pull-ups or 1.0 kohm pull-downs to prevent PHYAD latch errors if MAC signals drive during reset. For safety-critical drivetrain Ethernet, designers should migrate to Microchip's AEC-Q100 LAN8770 instead.
Recommended
MCU/MPU Development Boards (RMII add-on)
The KSZ8081RNACA-TR is a common PHY on STM32, SAMD, i.MX RT, and PIC32 development boards because the 24-QFN 4x4 mm footprint fits standard 100-mil 2x12 header shields, and the RMII interface aligns with most modern MCU Ethernet MACs. The 25 MHz crystal reference (or 50 MHz RMII clock input option) supports both crystal-oscillator and clock-from-MAC designs, which is convenient for boards that need to support multiple host architectures. Engineers evaluating the part can use Microchip's EVB-KSZ8081RNACA reference design as a schematic template.
Recommended
Recommended Products Summary
Engineering reference data for KSZ8081RNACA-TR — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | KSZ8081RNACA | KSZ8081RNDCA-TR | KSZ8081RNDCA | KSZ8061RNBW |
|---|---|---|---|---|---|
| Package | 24-QFN (4x4 mm) | 24-QFN (4x4 mm) - same | 24-QFN (4x4 mm) - same | 24-QFN (4x4 mm) - same | 32-QFN (5x5 mm) - different |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| MAC Interface | RMII v1.2 | RMII v1.2 | RMII v1.2 | RMII v1.2 | RMII v1.2 |
| Supply Voltage | 3.135 V to 3.465 V (3.3 V) | 3.135 V to 3.465 V | 3.135 V to 3.465 V | 3.135 V to 3.465 V | 3.3 V (range per datasheet) |
| On-chip 1.2 V LDO | Yes | Yes | Yes | Yes | Yes |
| Auto-MDIX | HP Auto-MDIX | HP Auto-MDIX | HP Auto-MDIX | HP Auto-MDIX | HP Auto-MDIX |
| Data Rate | 10/100 Mbps | 10/100 Mbps | 10/100 Mbps | 10/100 Mbps | 10/100 Mbps |
| Operating Temperature | -40 C to +85 C (industrial) | -40 C to +85 C | -40 C to +85 C | -40 C to +85 C | 0 C to +70 C (commercial) |
| Packaging Form | Tape & Reel (-TR) | Tray (no -TR suffix) | Tape & Reel | Tray | Tape & Reel |
Key Differentiators
- 24-QFN 4x4 mm footprint saves ~40% PCB area vs MII PHYs (vs KSZ8081MNXCA (32-QFN 5x5 mm))
- On-chip 1.2 V LDO eliminates an external regulator (vs LAN8720A-CP)
- HP Auto-MDIX on all four differential pairs (vs KSZ8061RNBW)
Design Notes
Place the 24.9 ohm (1% tolerance) RBIAS resistor within 5 mm of pin 15 with a ground via placed at the resistor's GND end - the bias current sets the analog reference for the line driver and is sensitive to leakage. Route the TD+/TD- and RD+/RD- differential pairs as 100 ohm differential impedance with 2 W spacing to other signals, keeping the pair length matching to within 2 mm. Place the 25 MHz crystal within 5 mm of the XI/XO pins with a continuous ground pour underneath the analog block. Add 0.1 uF and 10 uF decoupling capacitors as close as possible to each VDDIO and VDDA pin.
Per the Microchip datasheet, the strap-in pins (PHYAD[1:0] and CONFIG on shared RMII signal pins) are latched at the de-assertion of reset. If the host MAC drives RMII signals high or low during reset, the PHYAD may be latched to an unintended value. Add an external 4.7 kohm pull-up or 1.0 kohm pull-down on each shared strap pin if there is any chance the MAC will be active during the PHY's reset window. Failing to address this is the single most common source of 'unreachable PHY' debug tickets on first prototypes.
Estimated: cable reach and link reliability depend heavily on the magnetics selection and PCB layout. Use a 1:1 turns-ratio isolation transformer with common-mode choke rated for 100BASE-TX (such as the HR601680 or equivalent). The 100 ohm differential impedance of the CAT-5 traces should be verified with a TDR after PCB fab, and the magnetics-to-RJ-45 stub should be kept under 8 mm. For EMI compliance (FCC Class B, EN 55022), the chassis ground and earth ground separation must follow the magnetics datasheet's recommended footprint, with a 4.7 nF Y-cap and 1 Mohm resistor in parallel bridging the two ground domains.
Compliance Information
RoHS and REACH compliant per Microchip product page and DigiKey compliance field. Not AEC-Q100 qualified - for safety-critical automotive designs migrate to Microchip's LAN8770 family. Lead-free matte-tin plating. JEDEC J-STD-020 reflow compatibility (MSL level not explicitly provided in source data, marked [DATA_NEEDED] in specs).
