Using the STK525
STK525 Hardware User Guide
2-9
7608A–AVR–04/06
2.2.3
VBUS Generator Setting
When using the AT90USBxxx microcontroller in USB host mode. The STK525 should
provide a 5V power supply over the VBUS pin of its USB mini AB connector.
A couple of transistors on the STK525 allows the UVCON pin of the AT90USBxxx to
control the VBUS generation (See Figure 2-4). In this mode the STK525 is powered by
external power supply source (J6 or STK500 expand0/1 connectors). JP7 allows to
select the 5V source used by the VBUS generator.
Figure 2-4 . VBUS generator schematic
Table 2-2 . VBUS Generator Setting
M1
FDV304P/FAI
R33
100k
VTG
STK
Ext
Q2
BC847B
-
C34
4.7uF
2
1
3
JP7
VBUS gen
R32
10k
UVCON
VBUS
“Vbus Gen”
Jumper position
STK525 power supply
Comments
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“Ext”
External power supply from J6
This is the default configuration.
The VBUS generator source is the
on-board 5V regulator.
“Stk”
External power supply from
Expand0/1 (connected to a STK500)
The VBUS generator source is the
STK500.
Note:
The “Vtarget” setting of STK500
should be set to “5V”.
Vbus
Gen
Ext
Stk
Vbus
Gen
Ext
Stk
