UM245R Datasheet, PDF (13/19 Pages) Future Technology Devices International Ltd. – USB-Parallel FIFO Development Module Incorporating FTDIChip-ID™ Security Dongle

6. Module Configurations
6.1 Bus Powered Configuration
1 _J1
24
Page 13
J2
12
13
Figure 5 - Bus Powered Configuration
Figure 5 illustrates the UM245R in a typical USB bus powered design configuration. This can easily be done by fitting
the jumper link on J2, as shown above. The UM245R is supplied in this configuration by default.
A USB Bus Powered device gets its power from the USB bus. Basic rules for USB Bus power devices are as follows –
i) On plug-in to USB, the device must draw no more than 100mA.
ii) On USB Suspend the device must draw no more than 500μA.
iii) A Bus Powered High Power USB Device (one that draws more than 100mA) should use the PWREN# pin to keep
the current below 100mA on plug-in and 500μA on USB suspend.
iv) A device that consumes more than 100mA can not be plugged into a USB Bus Powered Hub.
v) No device can draw more that 500mA from the USB Bus.
Interfacing the UM245R module to a microcontroller (MCU), or other logic for a bus powered design would be done
in exactly the same way as for a self powered design (see Section 6.2), except that the MCU would take its power
supply from the USB bus (either the 5V on the USB pin, or the 3.3V on the 3V3 pin).
UM245R USB-Parallel FIFO Development Module Datasheet Version 1.02
© Future Technology Devices International Ltd. 2005