FT260Q-R Datasheet, PDF (35/61 Pages) Future Technology Devices International Ltd. – HID-class USB to UART/I2C Bridge IC

FT260 HID-CLASS USB TO UART/I2C BRIDGE IC
Version 1.1
Document No.: FT_001272 Clearance No.: FTDI#484
7.2 Self Powered Configuration with 5V Source Input
Figure 7.2 Self Powered Configuration with 5V Source Input
Figure 7.2 illustrates the FT260 in a typical USB2.0 self-powered configuration. A USB self-powered
device gets its power from its own power supply, 5V, and does not draw current from the USB bus. The
basic rules for USB self-powered devices are as follows –
i)
A self-powered device should not force current down the USB bus when the USB host or hub
controller is powered down.
ii)
A self-powered device can use as much current as it needs during normal operation and USB
suspend as it has its own power supply.
iii)
A self-powered device can be used with any USB host, a bus powered USB hub or a self-
powered USB hub.
VCCIN is the power source for the FT260 and will source power from its own power supply. When the I/O
voltage level is +3.3V, users can directly connect VOUT3V3 to VCCIO without an external regulator. The
power descriptors in the embedded eFUSE of the FT260 or in the external EEPROM should be
programmed as self-powered.
In order to comply with the first requirement above, the USB bus power (USB connector pin 1) is used to
control the VBUS_DET pin of the FT260 device. VBUS_DET is a 5V-tolerant input pin and can directly
connect to VBUS without an on-board voltage divider circuit. When the USB host or hub is powered up an
internal 1.5kΩ resistor on DP is pulled up to +3.3V, thus identifying the device to the USB host or hub.
When the USB host or hub is powered off, the VBUS_DET pin will be low and the FT260 is held in a
suspend state. In this state the internal 1.5kΩ resistor is not pulled up to any power supply (hub or host
is powered down), so no current flows down DP via the 1.5kΩ pull-up resistor. Failure to do this may
cause some USB host or hub controllers to power up erratically.
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