Enhanced 1-Ch Full-Speed USB UART


The XR21B1420 is an enhanced Universal Asynchronous Receiver and Transmitter (UART) bridge to USB interface. The USB interface is fully compliant to the USB 2.0 (Full-Speed) specification with 12 Mbps USB data transfer rate. The USB interface also supports USB suspend, resume and remote wakeup operations. The USB Vendor ID, Product ID, power mode, remote wakeup support, maximum power, and numerousother settings may be programmed in the on-chip OTP memory via the USB interface.

The XR21B1420 includes an internal oscillator and does not require an external crystal/oscillator. Any UART baud rate up to 12 Mbps may be generated with this internal clock and the fractional baud rate generator. The UART pins may also be configured as GPIO; direction, state, output driver type and input pull-up or pull-down resistors are programmed either through on chip OTP, or on the fly via memory mapped registers.

Large 512-byte TX and RX FIFOs prevent buffer overflow errors and optimize data throughput. Automatic half-duplex direction control and optional multi drop (9-bit) mode simplify both hardware and software in half-duplex RS-485 applications.

The XR21B1420 uses the native OS CDC-ACM driver or an Exar supplied custom driver. Exar provides WHQL/HCK-certified software drivers for Windows 2000, XP, Vista, 7, 8, 8.1 as well as software drivers for Windows CE, Linux and Mac OS X. Full source code is available.

The XR21B1420 operates from a single 5V or 3.3V power supply. When powered with 5V input, a regulated 3.3V output is supplied.

For UART technical support or to obtain an IBIS model for this product, please email Exar's UART Technical Support group.

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  • ±15kV ESD on USBD+/USBD-
  • USB 2.0 Compliant, Full-Speed (12Mbps)
  • Unique pre-programmed USB serial number
  • Internally generated 48MHz core clock
  • Enhanced UART features
    • Baud rates up to 12 Mbps
    • Fractional Baud Rate Generator
    • 512-byte TX and 512-byte RX FIFOs
    • Auto Hardware / Software Flow Control
    • Multidrop and Half-Duplex Modes
    • Auto RS-485 Half-Duplex Control
    • Selectable GPIO or Modem I/O
  • Up to 10 GPIOs
  • 5V tolerant GPIO inputs
  • Suspend state GPIO configuration
  • Configurable clock output
  • 28-pin QFN package
  • Industrial -40°C to +85°C Temperature Range


  • Building Automation
  • Security Systems
  • Factory and Process Control
  • ATM Terminals
  • USB to Serial Controllers

Download Software Drivers

Design Tools

Evaluation Hardware and Software
Technical Library


Pkg Code Details Quantities Dimensions PDF
QFN28 5x5
  • JEDEC Reference: MO-220
  • MSL Pb-Free: L2 @ 260ºC
  • MSL SnPb Eutectic: n/a
  • ThetaJA: 33.0ºC/W
  • Bulk Pack Style: Canister
  • Quantity per Bulk Pack: n/a
  • Quantity per Reel: 3000
  • Quantity per Tube: n/a
  • Quantity per Tray: 490
  • Reel Size (Dia. x Width x Pitch): 330 x 12 x 8
  • Tape & Reel Unit Orientation: Pin 1 at sprocket hole.
  • Dimensions: mm
  • Length: 5.00
  • Width: 5.00
  • Thickness: 0.90
  • Lead Pitch: 0.50

Parts & Purchasing

Part Number Pkg Code RoHS Min Temp Max Temp Status Buy Now Order Samples
XR21B1420IL28-F QFN28 5x5 -40 85 Active
XR21B1420IL28TR-F QFN28 5x5 -40 85 Active
XR21B1420IL28-0A-EVB Board Active
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Part Status Legend
Active - the part is released for sale, standard product.
EOL (End of Life) - the part is no longer being manufactured, there may or may not be inventory still in stock.
CF (Contact Factory) - the part is still active but customers should check with the factory for availability. Longer lead-times may apply.
PRE (Pre-introduction) - the part has not been introduced or the part number is an early version available for sample only.
OBS (Obsolete) - the part is no longer being manufactured and may not be ordered.
NRND (Not Recommended for New Designs) - the part is not recommended for new designs.
Distribution Date Description File
03/28/2017 Change QFN E-pad dimension range from 3.15~3.35mm to 2.60~3.60mm, assembly in ANST. PCN 17-0310-02 ANST-1033.pdf
01/31/2017 Addition of qualified 12 inch wafer processing line in Global Foundries, in addition to the currently qualified 8 inch wafer processing. Note: Reliability report will be available February 17, 2017. PCN 16-0731-01-01 12 inch Global Foundries-1033.pdf