xr21b1411 Exar Corporation, xr21b1411 Datasheet - Page 4

• Manufacturer Part Number: xr21b1411
• Description: Enhanced 1-ch Full-speed Usb Uart
• Manufacturer: Exar Corporation

XR21B1411
ENHANCED 1-CH FULL-SPEED USB UART
N
Pin Description
Power / Ground Signals
OTE
VBUS_SENSE
LOWPOWER
: Pin type: I=Input, O=Output, I/O= Input/output, PWR=Power, OD=Output Open Drain.
VIO_REF
N
GND
GND
VCC
NC
AME
1
16-QFN
Center
P
Pad
12
16
13
IN
11
2
#
O
T
Pwr
Pwr
Pwr
Pwr
YPE
I
The LOWPOWER pin will be asserted whenever it is not safe to draw the
amount of current requested 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.
The LOWPOWER pin will be de-asserted whenever it is safe to draw the
amount of current 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.
VBUS Sense input. This pin is used to disable the pull-up resistor on the
USBD+ signal when VBUS is not present. In bus-powered mode, this
pin should be left unconnected. 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 may be enabled via the OTP.
No Connect
Reference voltage for the modem I/O signals. The voltage range for
VIO_REF is + 1.6V to + 3.6V.
5V power supply. The voltage range for VCC is + 4.4V to + 5.25V.
Power supply common, ground.
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.
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.
4
D
ESCRIPTION
REV. 1.1.0