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Evaluation board hardware UM0529
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2 Evaluation board hardware
All the hardware components except the transceiver IC are the same for the STUSB02E and
STUSB03 evaluation boards. The evaluation boards are comprised of one mini-B USB
connector, one USB controller, one USB transceiver, two 2-to-4 demultiplexers and all
required discrete components (pull-up resistors, series resistors and power supply
capacitors). The device can be configured through a set of jumpers and the main signals
can be accessed through test points.
The evaluation board is powered from a USB mini-B or optionally from an external supply.
The transceiver STUSB02EQR/ STUSB03EQR is connected at the USB communication
lines of the microcontroller. The USBVCC 3.3 V is obtained from the controller for providing
the VIF to the transceiver and also the supply to 74LCX139. Since the ST72F63B is a USB
low-speed microcontroller, therefore the pull-up resistor is connected to the D- pin of the
transceiver. Hence, STUSB02E / STUSB03 acts as a low-speed transceiver. Also the SPD
pin of the transceiver is connected to GND for low-speed selection.
The 74LCX139MTR is used to convert 5 V signals from the microcontroller to 3.3 V signals
to STUSB02E/STUSB03E. This device is used because some signals need polarity
conversion whereas other signals just need the level conversion. This is explained in
Section 3.3: 74LCX139MTR low voltage dual 2-to-4 decoder/demultiplexer U2,U3 .
Figure 3. STUSB02E/ STUSB03 evaluation board block diagram
S TU S B02E/
S TU S B0 3 E
U S B L S
Tran s ceiver
U5
Power pin s (V
BU S
, V
IF
)
V
BU S
, DP, DM
S T72F6 3 B
U S B
Controller
U1
LED s
S witche s
Mini-B
connector
74LCX1 3 9MTR
U2
74LCX1 3 9MTR
U 3
Confi g uration
Jumper s
S ign a l s
a t 3 . 3 V
S ign a l s
a t 5V
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