XR21B1411_17 Datasheet, PDF (5/32 Pages) Exar Corporation – ENHANCED 1-CH FULL-SPEED USB UART

XR21B1411
ENHANCED 1-CH FULL-SPEED USB UART
Pin Description
REV. 1.2.1
NAME
16-QFN
PIN #
Miscellaneous Signals
LOWPOWER
1
VBUS_SENSE
11
NC
2
Power / Ground Signals
VIO_REF
12
VCC
GND
GND
16
13
Center
Pad
TYPE
DESCRIPTION
O
The LOWPOWER pin will be asserted whenever it is not safe to draw the
amount of current requested from VBUS in the Device Maximum Power
field of the Configuration Descriptor.
The LOWPOWER pin will behave differently for a low power device and
a high power device.
■ Low-power device (<= 1 unit load or 100 mA i.e.
bMaxPower <= 0x32): LOWPOWER pin is asserted when
the USB UART is in suspend mode.
■ High-power deivce (bMaxPower > 0x32): LOWPOWER
pin is asserted when the USB UART is in suspend mode
or when it is not yet configured.
The LOWPOWER pin will be de-asserted whenever it is safe to draw the
amount of current from VBUS requested in the Device Maximum Power
field.
The default active low polarity may be changed via the OTP. Connect
this pin to VIO_REF or to ground through a weak (10K) pull-up or pull-
down resistor to match the polarity of the asserted state in high power
applications. In low power applications, no external resistor is required.
I
VBUS Sense input. This pin is used to disable the pull-up resistor on the
USBD+ signal when VBUS is not present in self-powered mode. In self-
powered mode, the VBUS from the USB connector should be connected
to this pin through a voltage divider circuit (VBUS = 5V), such that
VBUS_SENSE = VIO_REF, using large resistance values to minimize
power. It should also be decoupled by a 0.1 uF capacitor. This feature
must be enabled via the OTP. In bus-powered mode, this pin is ignored
but should be tied to a defined logic state.
No Connect
Pwr _{Reference voltage for the modem I/O signals. The voltage range for}
VIO_REF is + 1.6V to + 3.6V.
Pwr _{5V power supply. Input voltage range for VCC is + 4.4V to + 5.25V.}
Pwr _{Power supply common, ground.}
Pwr _{The center pad on the back side of the QFN package is metallic and}
should be connected to GND on the PCB. The thermal pad size on the
PCB should be the approximate size of this center pad and should be
solder mask defined. The solder mask opening should be at least
0.0025" inwards from the edge of the PCB thermal pad.
NOTES:
1. Pin type: I=Input, O=Output, I/O= Input/output, PWR=Power, OD=Output Open Drain.
2. IO pins are undefined during USB bus reset and POR (Power On Reset). To ensure defined state during reset
conditions, use a weak external resistor to pull to the desired state.
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