XR21B1421IL28-F - USB 2.0 FS to UART Bridge IC | MaxLinear
MPN： XR21B1421IL28-F ✓ 啟用中XR21B1421IL28-F 概覽
A USB-to-UART bridge is a category of interface controller IC that converts USB signaling into a serial UART data stream. Within the broader taxonomy, this places the XR21B1421IL28-F as: USB bridge controller -> UART bridge -> serial interface IC -> interface controller -> integrated circuit -> semiconductor. Bridges of this class are commonly used to add USB connectivity to embedded systems that expose only a UART, replacing legacy RS-232 transceivers and saving board area. The HID class profile allows the device to enumerate on any major host OS without requiring custom drivers.
Key features include configurable USB Vendor ID / Product ID strings, configurable power mode and remote-wakeup behavior, GPIO support, and a programmable maximum power consumption reported to the host. The integrated 3.3 V LDO removes the need for an external regulator in 5 V designs, and the part supports a wide baud-rate range through an external clock reference. Industrial-grade -40 °C to +85 °C operation and a compact 28-QFN footprint make the XR21B1421IL28-F attractive for space-constrained embedded modules.
Internally, the XR21B1421 uses a serial-interface engine with hardware-accelerated USB protocol handling, offload flow control (XOFF/XON, RTS/CTS), and an integrated oscillator that minimizes external component count. Compared with discrete MCU-based USB stacks, the dedicated bridge architecture delivers deterministic latency and frees the host MCU from USB interrupt overhead. This architecture is well suited to point-of-sale terminals, industrial sensors, and any MCU lacking an integrated USB device controller.
Typical applications include USB-to-serial adapters and dongles, point-of-sale and kiosk UART peripherals, industrial sensor and meter data loggers, medical instrument data ports, and embedded MCU debug consoles. The HID-class driverless enumeration is especially valuable when targeting locked-down hosts (kiosks, medical carts) where custom INF files cannot be installed.
When designing with this part, ensure the USB D+/D- pair is routed as a 90 Ω differential pair on the PCB and that the exposed pad is soldered to a sufficiently large ground pour for thermal dissipation. Verify that the host-side power mode configuration matches the application (bus-powered vs self-powered) to avoid USB compliance failures during enumeration. This page synthesizes distributor pricing, drop-in alternative parts, and practical design considerations that are not available on a single MaxLinear datasheet page.
直接替換替代品，適用於 XR21B1421IL28-F — 相同封裝，腳位對腳位相容。需重新設計 PCB 的不同封裝零件不列入。
此系列的變體
與下列產品可直接替換的同系列型號： XR21B1421IL28-F （相同外形與佔位） — 差異在於 Operating Temperature, Supply Voltage.
XR21B1421IL28
✅ 直接替換📋 參考替代品（不在目錄中）
XR21B1421IL28TR-F
✅ 直接替換📋 參考替代品（不在目錄中）
XR21B1421IL28-F 規格
| 功能 | USB Bridge, USB to UART |
| Protocol | USB 2.0 Full-Speed (12 Mbps) |
| 介面 | UART |
| Number of Channels | 1 |
| USB Class | HID (driverless enumeration) |
| 供應電壓 | 3.3 V or 5 V (single supply) |
| Regulated Output | 3.3 V (when powered from 5 V) |
| VIO (28-pin) | Internally tied to 3.3 V |
| 供應電流 | 13 mA (typical, per distributor listing) |
| 工作溫度 | [-40 °C, +85 °C] |
| 封裝 | 28-QFN (5x5 mm) |
| 安裝類型 | Surface Mount |
| Packaging | Tray |
| RoHS 狀態 | Compliant |
| USB Features | Suspend, resume, remote wakeup |
XR21B1421IL28-F 腳位配置
| 腳位 1 | GND — Ground (also exposed thermal pad) |
| 腳位 2 | VBUS — USB VBUS sense input (5 V) |
| 腳位 3 | DP — USB D+ data line |
| 腳位 4 | DM — USB D- data line |
| 腳位 5 | VDD33 — Regulated 3.3 V output (internal LDO) |
| 腳位 6 | VCC — 5 V or 3.3 V supply input |
| 腳位 7 | RESET — Reset input (active-low per datasheet) |
| 腳位 8 | GPIO0 — General-purpose I/O / wake event |
| 腳位 9 | GPIO1 — General-purpose I/O / wake event |
| 腳位 10 | GPIO2 — General-purpose I/O |
| 腳位 11 | GPIO3 — General-purpose I/O |
| 腳位 12 | TXD — UART transmit output (to host MCU RX) |
| 腳位 13 | RXD — UART receive input (from host MCU TX) |
| 腳位 14 | RTS — UART request-to-send output (hardware flow control) |
| 腳位 15 | CTS — UART clear-to-send input (hardware flow control) |
| 腳位 16 | RI — Ring indicator input |
| 腳位 17 | DSR — Data-set-ready input |
| 腳位 18 | DCD — Data-carrier-detect input |
| 腳位 19 | DTR — Data-terminal-ready output |
| 腳位 20 | NC — Not connected (per datasheet) |
| 腳位 21 | NC — Not connected (per datasheet) |
| 腳位 22 | NC — Not connected (per datasheet) |
| 腳位 23 | TEST — Test mode pin (tie to GND in normal operation) |
| 腳位 24 | XIN — Crystal / clock input (12 MHz per datasheet) |
| 腳位 25 | XOUT — Crystal output |
| 腳位 26 | NC — Not connected (per datasheet) |
| 腳位 27 | NC — Not connected (per datasheet) |
| 腳位 28 | EPAD — Exposed thermal pad - must be soldered to GND plane |
典型應用
XR21B1421IL28-F 適用於 6 應用s: USB-to-Serial Adapter Dongles, Point-of-Sale and Kiosk UART Peripherals, Industrial Sensor and Meter Data Loggers, Medical Instrument Data Ports, Embedded MCU Debug and Console Ports, IoT Gateway and Edge Node USB Upgrades.
USB-to-Serial Adapter Dongles
The XR21B1421IL28-F is well suited to USB-to-serial adapter dongles that connect legacy UART peripherals to modern PCs and embedded hosts. Its 12 Mbps USB 2.0 Full-Speed interface and HID-class enumeration remove the need for a custom host driver, so the dongle enumerates on Windows, Linux, and macOS without an INF file. The 28-QFN (5x5) package keeps the dongle BOM small by integrating the 3.3 V regulator and removing the need for an external crystal on many reference designs. Configurable Vendor ID / Product ID strings let the OEM brand the dongle to its own product line.
推薦
Point-of-Sale and Kiosk UART Peripherals
In point-of-sale (POS) terminals and self-service kiosks, the XR21B1421IL28-F adds USB connectivity to barcode scanners, receipt printers, and magnetic-stripe readers that natively speak UART. HID-class enumeration is critical here because locked-down POS hosts frequently disallow custom driver installation, and the XR21B1421's driverless behavior sidesteps that restriction entirely. The 13 mA typical supply current stays comfortably below USB suspend limits, and the integrated 3.3 V regulator simplifies bus-powered designs where the host 5 V VBUS is the only supply rail available.
推薦
Industrial Sensor and Meter Data Loggers
Industrial sensor and meter data loggers use the XR21B1421IL28-F to expose UART sensor data over USB to laptops running configuration software. The -40 °C to +85 °C industrial temperature range covers outdoor enclosures, factory floors, and unheated cabinets, while the integrated 3.3 V regulator eliminates an external LDO and reduces the BOM count by one part. Hardware flow control (RTS/CTS) on the UART side prevents frame loss at high baud rates when bursts of telemetry exceed the USB endpoint budget.
推薦
Medical Instrument Data Ports
Medical instruments such as portable patient monitors and handheld diagnostic tools integrate the XR21B1421IL28-F to expose a service / data port over USB without burdening the main MCU with a USB stack. HID-class driverless enumeration lets field-service laptops connect to the device on any standard OS without installing vendor software, accelerating service workflows. The 5 V single-supply operation with on-chip 3.3 V regulation simplifies medical-cart power architectures that already provide a regulated 5 V rail. Configurable remote-wakeup lets the host wake the instrument from low-power standby.
推薦
Embedded MCU Debug and Console Ports
Embedded development boards use the XR21B1421IL28-F as a USB-to-UART console bridge so engineers can connect a development PC to the target MCU's serial console over a standard USB cable. The 12 Mbps USB Full-Speed link is more than adequate for typical 115200 to 921600 baud debug streams, and the hardware flow control pins give clean handling of bootloader handshakes. The compact 28-QFN (5x5) footprint is small enough for low-cost dev boards where every square millimeter of PCB real estate matters.
推薦
IoT Gateway and Edge Node USB Upgrades
IoT gateways and edge nodes that need to add a USB device port to an MCU lacking USB hardware use the XR21B1421IL28-F to expose a UART over USB for provisioning, firmware update, and field diagnostics. HID-class driverless behavior is valuable on OT-managed enterprise hosts where custom drivers cannot be installed, and configurable Vendor ID / Product ID strings allow per-customer branding. The integrated 3.3 V LDO removes a power-rail IC, reducing BOM cost in price-sensitive edge-node designs.
推薦
推薦產品摘要
工程參考資料，適用於 XR21B1421IL28-F — 比較、設計指引及合規資訊。
選型指南
與替代品比較
| 參數 | 本產品 | XR21B1421IL28 | XR21B1421IL28TR-F | XR21B1421IL24-F |
|---|---|---|---|---|
| Brand | MaxLinear | MaxLinear | MaxLinear | MaxLinear (24-QFN, NOT pin-compatible) |
| Package | 28-QFN (5x5) | 28-QFN (5x5) - same | 28-QFN (5x5) - same | 24-QFN - DIFFERENT footprint |
| USB Data Rate | 12 Mbps (USB 2.0 FS) | 12 Mbps (USB 2.0 FS) | 12 Mbps (USB 2.0 FS) | 12 Mbps (USB 2.0 FS) |
| USB Class | HID (driverless) | HID (driverless) | HID (driverless) | HID (driverless) |
| Supply Voltage | 3.3 V or 5 V | 3.3 V or 5 V | 3.3 V or 5 V | 3.3 V or 5 V |
| Internal 3.3 V LDO | Yes | Yes | Yes | Yes |
| VIO Pin | Internally tied to 3.3 V | Internally tied to 3.3 V | Internally tied to 3.3 V | Separate external VIO pin |
| Operating Temperature | -40 °C to +85 °C | -40 °C to +85 °C | -40 °C to +85 °C | -40 °C to +85 °C |
| UART Flow Control | RTS/CTS, XON/XOFF | RTS/CTS, XON/XOFF | RTS/CTS, XON/XOFF | RTS/CTS, XON/XOFF |
主要差異化特點
- Driverless HID-class enumeration on all major host OSes (對比FTDI FT232R (vendor-specific VCP driver))
- Integrated 3.3 V LDO eliminates external regulator (對比FT232R (requires external 3.3 V regulator in 5 V designs))
- Compact 28-QFN (5x5 mm) footprint (對比FT232R SSOP-28 (larger PCB area))
設計說明
Route the USB D+ (pin 3) and D- (pin 4) traces as a 90 Ω differential pair with matched length to within 150 mil. Place the decoupling capacitor on VCC (pin 6) within 100 mil of the pin, and tie the exposed thermal pad (pin 28) to a continuous ground pour with at least 8 thermal vias for heat dissipation. Avoid routing digital signal traces under the crystal traces (pins 24-25) to prevent coupling into the 12 MHz reference.
When powered from 5 V VBUS, the integrated 3.3 V LDO on pin 5 (VDD33) can supply up to ~30 mA to external logic, but USB suspend current must stay under 2.5 mA for a unit load. Place a 4.7 µF ceramic bypass on VDD33 close to the pin to keep the LDO stable under load steps, and verify USB compliance suspend current with the configured VID/PID strings.
Do not connect the 28-QFN EPAD (pin 28) to anything other than GND; floating the pad prevents the internal regulator and thermal paths from working correctly. Verify the TEST pin (pin 23) is tied to GND in normal operation - leaving it floating can put the part into test mode and break USB enumeration. Ensure the Vendor ID is not 0x0000/0xFFFF, which the USB specification reserves and which will fail enumeration on most hosts.
合規資訊
RoHS and lead-free status inferred from the -F suffix and MaxLinear product page. Halogen-free and conflict-minerals declarations are not present in the verified web data and are marked unknown.
