XR21B1422
Enhanced 2-Ch Full-Speed USB UART
General Description
FEATURES
The XR21B1422 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 numerous
other settings may be programmed in the on-chip OTP memory via the
USB interface.
• ±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 from 300 bps 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 per channel
• 5V tolerant GPIO inputs
• Suspend state GPIO configuration
• Configurable clock output
• 40-pin QFN package
The XR21B1422 includes an internal oscillator and does not require an
external crystal/oscillator. Any UART baud rate from 300 bps to 12 Mbps
may be generated with this internal clock and the fractional baud rate
generator.
The UART pins for each port 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. Wide mode allows for each individual received
character to be monitored for errors.
• Industrial -40°C to +85°C Temperature
Range
APPLICATIONS
• Building Automation
• Security Systems
• Factory and Process Control
• ATM Terminals
The XR21B1422 uses the native OS CDC-ACM driver or a MaxLinear
supplied custom driver. MaxLinear provides WHQL-certified software
drivers for Windows XP, Vista, 7, 8, 8.1,10, and 11 as well as custom
software drivers for Linux. Full source code is available.
• USB to Serial Controllers
Ordering Information - page 62
Block Diagram
VIO
Internal
Oscillator
(48MHz)
USB
Fractional
BRG
512-byte
TX FIFO
TX
512-byte
RX FIFO
RX
Throughput Comparison
1840k
1610k
1380k
USB Slave Interface
USB
Descriptors
Internal
Status and
Control
Registers
Competitor
MaxLinear
1150k
GPIOs/
Modem IO
OTP
920k
690k
460k
230k
UART Ch A
LDO
3V3
• www.maxlinear.com • 272DSR00
UART Ch B
(same as Ch A)
0k
230k
460k
920k
Data Rate (bps)
1840k
XR21B1422
Absolute Maximum Ratings
Operating Conditions
Stresses beyond those listed under Absolute Maximum
Ratings may cause permanent damage to the device.
Exposure to any Maximum Rating may affect device
reliability and lifetime.
Operating Temperature Range.....................-40°C to +85°C
Supply Voltage (VCC_REG)......................................+5.75V
Supply Voltage (VCC, VIO)............................................+4V
Input Voltage (VBUS_SENSE).......................-0.3 to +5.75V
Input Voltage (All other pins)............................-0.3 to +5.6V
Junction Temperature.................................................125°C
Electrical Characteristics
Unless otherwise noted: TA = -40°C to +85°C, VCC_REG = +4.4V to +5.25V or +3.0V to +3.6V, VIO = +1.8V to +3.6V.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
15
23
mA
0.85
1.25
mA
3.3
3.6
V
Power
ICC
Power Supply Current
ISUSP
Suspend Mode Current
VOUT
Regulated Output Voltage (VCC pin)
VCC_REG = +4.4V to +5.25V
(Does not include current that VOUT sources
to external devices or to VIO)
VCC_REG = +4.4V to +5.25V.
Maximum output current = 200 mA including
the supply current of the XR21B1422.
3
UART, USB_STAT and GPIO Pins
VIL
Input Low Voltage
-0.3
0.25*
VIO
V
VIH
Input High Voltage
0.70*
VIO
5.5
V
VOL
Output Low Voltage
IOL = 1mA, VIO = +1.6V
0.3
V
IOL = 4mA, VIO = +3.6V
0.5
V
VOH
Output High Voltage
IOH = -400uA, VIO = +1.6V
1.3
VIO
V
IOH = -1.5mA, VIO = +3.6V
2.8
VIO
V
IIL
Input Low Leakage Current
VIO = +3V to +3.6V, VCC_REG = +4.4V to
+5.25V, VINPUT = 0V
±10
µA
IIH
Input High Leakage Current
VIO = +3V to +3.6V, VCC_REG = +4.4V to
+5.25V, VINPUT = +3.3V
±10
µA
VIO = +3V to +3.6V, VCC_REG = +4.4V to
+5.25V, VINPUT = +5.5V
±120
µA
5
pF
CIN
272DSR00
Input Pin Capacitance
2
Rev. 1E
XR21B1422
Symbol
Parameter
Conditions
Min
Typ
Max
Units
USB I/O Pins
VIL
Input Low Voltage
-0.3
0.8
V
VIH
Input High Voltage
2.0
5.5
V
VOL
Output Low Voltage
External 15kΩ to GND on USBD+ and
USBD- pins
0
0.3
V
VOH
Output High Voltage
External 15kΩ to GND on USBD+ and
USBD- pins
2.8
3.6
V
VDrvZ
Driver Output Impedance
28
44
Ω
272DSR00
3
Rev. 1E
XR21B1422
RXA
GPIOA5/RTSA#/RS485A
GPIOA4/CTSA#
GPIOA3/DTRA#
GPIOA2/DSRA#
GPIOA1/CDA#
GPIOA0/RIA#/RWKA#
34
33
32
31
TXA
35
GPIOA6/CLKA
36
38
37
39
1
MaxLinear
XR21B1422
30
GPIOB0/RIB#/RWKB#
29
GPIOB1/CDB#
28
GPIOB2/DSRB#
GPIOA9/RXTA
2
NC
3
NC
4
27
GPIOB3/DTRB#
GND
5
26
GPIOB4/CTSB#
USBD+
6
25
GND
USBD-
7
24
VIO
VIO
8
23
GPIOB5/RTSB#/RS485B
VCC
9
22
RXB
21
TXB
E_PAD
USB_STAT1
GPIOB9/RXTB
NC
USB_STAT2
GPIOB6/CLKB
NC
GPIOB7/RS485B
16
GPIOB8/TXTB
15
20
14
19
13
18
12
4
17
11
RESET#
10
VBUS_SENSE
VCC_REG
272DSR00
40
GPIOA8/TXTA
GPIOA7/RS485A
Pin Configuration
Rev. 1E
XR21B1422
Pin Assignments
Pin No.
Pin Name
Type
Description
1
GPIOA8/TXTA
I/O
General purpose I/O, or UART transmit data indicator. Defaults to GPIO input with internal pullup resistor. See “TXT and RXT Pins” on page 18. When configured as transmit indicator, this
pin will toggle at ~10Hz intervals while the UART is transmitting data.
2
GPIOA9/RXTA
I/O
General purpose I/O, or UART receive data indicator. Defaults to GPIO input with internal pullup resistor. See “TXT and RXT Pins” on page 18. When configured as receive indicator, this
pin will toggle at ~10Hz intervals while the UART is receiving data.
3
NC
-
No Connect. MaxLinear recommends to connect this pin to the ground.
4
NC
-
No Connect. MaxLinear recommends to connect this pin to the ground.
5
GND
6
USBD+
I/O
USB port differential data positive. This pin has internal pull-up resistor compliant to the USB
2.0 specification. The ESD protection on this pin is ±15kV HBM.
7
USBD-
I/O
USB port differential data negative. The ESD protection on this pin is ±15kV HBM.
8
VIO
PWR
I/O voltage input to the UART/GPIO pins. Must be between 1.8 and 3.6V. May be connected to
VCC (pin 12) if VCC_REG input voltage is 5V. See “USB Power Modes” on page 11.
9
VCC
PWR
3.3V power to the device, or 3.3V power output from the device when 5V power is supplied to
VCC_REG pin. 3.3V output power can source up to 200 mA maximum (including the device)
and should be decoupled by minimum of 4.7µF ceramic capacitor. See “USB Power Modes”
on page 11.
10
VCC_REG
PWR
5V or 3.3V power to the device. In bus-powered mode, connect VBUS (5V) power from the
USB host to this pin and to the VBUS_SENSE pin - see Figure 1.To conform to USB specifications, an inrush current limiting circuit is recommended. In self-powered mode, connect onboard 5V or 3.3V source to this pin and VBUS from the USB host to the VBUS_SENSE pin.
See Figure 2 and Figure 3. USB specification requires a minimum of 1uF and a maximum of
10uF of decoupling on VBUS power.
11
VBUS_SENSE
I
Must be connected to VBUS power from the USB host PC. This pin is used to disable the internal pull-up resistor on the USBD+ signal when VBUS is not present. In bus-powered mode,
connect VBUS (5V) power from the USB host to this pin and to the VCC_REG pin - see Figure
1. In self-powered mode, connect VBUS from the USB host to this pin. This pin must be
decoupled by a 4.7 uF tantalum capacitor.
12
RESET#
I/O OD
Active low open drain output. Asserted at power on or any time device is reset by either register or USB bus reset. As an input, must be asserted for at least 15µs to force a device reset.
Reset pulse width input of shorter than 15µs will have unknown effects. A weak internal pull-up
resistor provides noise immunity if left unconnected.
13
NC
14
USB_STAT2
272DSR00
PWR
O / OD
Power supply common, ground.
No Connect. MaxLinear recommends to connect this pin to the ground.
This pin has the same functionality as the USB_STAT1 pin. However, the default output for this
pin is active low polarity, asserted whenever the XR21B1422 is placed into a suspended state.
This default may be changed via the PIN_CFG_USB_STAT2 register.
5
Rev. 1E
XR21B1422
Pin No.
Pin Name
Type
Description
15
USB_STAT1
O
The USB_STAT1 output pin may be used to indicate any of three USB status conditions:
1. USB_STAT1 is asserted when the USB host asserts USB reset.
2. USB_STAT1 is asserted when the USB host PC places the XR21B1422 device into the suspended state.
3. USB_STAT1 is asserted when it is not safe to draw the amount of current requested in the
Device Maximum Power field of the Configuration Descriptor.
a. For a low power device (
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