FT232RN datasheet(20/40 Pages) FTDI

20 / 40 page

FT232RN USB UART IC Datasheet

Version 1.0

Document No.: FT_001521 Clearance No.: FTDI#571

On plug-in to USB, the device should draw no more current than 100mA.

ii)

In USB Suspend mode the device should draw no more than 2.5mA.

iii)

A bus powered high power USB device (one that draws more than 100mA) should use one of

the CBUS pins configured as PWREN# and use it to keep the current below 100mA on plug-in

and 2.5mA on USB suspend.

iv)

A device that consumes more than 100mA cannot be plugged into a USB bus powered hub.

No device can draw more than 500mA from the USB bus.

The power descriptors in the internal EEPROM of the FT232RN should be programmed to match the current

drawn by the device.

A ferrite bead is connected in series with the USB power supply to reduce EMI noise from the FT232RN and

associated circuitry being radiated down the USB cable to the USB host. The value of the Ferrite Bead

depends on the total current drawn by the application. A suitable range of Ferrite Beads is available from

Laird (www.laird.com), for example Laird Part # MI0805K400R-10.

Note: If using PWREN# (available using the CBUS) the pin should be pulled to VCCIO using a 10kΩ resistor.

6.2 Self Powered Configuration

Figure 6.2 Self-Powered Configuration

Figure 6.2 illustrates the FT232RN in a typical USB self-powered configuration. A USB self-powered device

gets its power from its own power supply, VCC, and does not draw current from the USB bus. The basic

rules for USB self-powered devices are as follows –

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.

The power descriptor in the internal EEPROM of the FT232RN should be programmed to a value of zero

(self-powered).

To comply with the first requirement above, the USB bus power (pin 1) is used to control the RESET# pin

of the FT232RN device. When the USB host or hub is powered up an internal 1.5kΩ resistor on USBDP is

FT232RN Datasheet(PDF) 20 Page - Future Technology Devices International Ltd.