XR21B1420IL28-0A Datasheet, PDF (4/60 Pages) Exar Corporation – Enhanced 1-Ch Full-Speed USB UART

Pin Assignments
Pin No.
Pin Name
1
GPIO1/CD#
2
GPIO0/RI#/RWK#
3
GND
4
USBD+
5
USBD-
6
VCC
7
VCC_REG
8
VBUS_SENSE
9
RESET#
10
GPIO9/RXT
11
USB_STAT2
12
USB_STAT1
13
NC
14
NC
15
NC
XR21B1420
Type
I/O
I/O
PWR
I/O
I/O
PWR
PWR
I
I/O OD
I/O
O / OD
O
-
-
-
Description
General purpose I/O, or UART Carrier-Detect input (active low). Defaults to GPIO input with
internal pull-up resistor.
General purpose I/O, or UART Ring-Indicator input (active low), or Remote Wakeup input.
Defaults to GPIO input with internal pull-up resistor. See “Remote Wakeup” on page 7.
Power supply common, ground.
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.
USB port differential data negative. The ESD protection on this pin is ±15kV HBM.
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 9.
5V or 3.3V power to the device. In bus-powered mode, connect VBUS power from the USB
host to this pin and to the VBUS_SENSE pin. See Figure 1. In self-powered mode, connect
on-board 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.
Must be connected to VBUS power from the USB host PC. This pin is used to disable the inter-
nal pull-up resistor on the USBD+ signal when VBUS is not present.
Active low open drain output. Asserted at power on or any time device is reset by either regis-
ter 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.
General purpose I/O, or UART receive data indicator. Defaults to GPIO input with internal pull-
up resistor. See “TXT and RXT Pins” on page 15. When configured as receive indicator, this
pin will toggle at ~10Hz intervals while the UART is receiving data.
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 XR21B1420 is placed into a suspended state.
This default may be changed via the PIN_CFG_USB_STAT2 register.
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 XR21B1420 device into the sus-
pend 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 (<=1 unit load or 100mA, bMaxPower <= 0x32), USB_STAT1 will be
asserted when the USB UART is in the suspend mode or when it is not yet configured.
b. For a high power device (bMaxPower > 0x32), USB_STAT1 will be asserted when the USB
UART is in the suspend mode or when it is not yet configured.
The assertion polarity and status condition are selectable via the PIN_CFG_STAT1 register.
The USB_STAT pin will be de-asserted whenever the selected condition(s) is/are not met. The
default output for this pin is active high polarity, asserted whenever the XR21B1420 is placed
into a suspended state.
No Connect.
No Connect.
No Connect.
© 2014 Exar Corporation
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Rev 1A