FT232RL datasheet(20/40 Pages) FTDI

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FT232R USB UART IC Datasheet

Version 2.16

Document No.: FT_000053 Clearance No.: FTDI# 38

6.2 Self Powered Configuration

Figure 6.2 Self-Powered Configuration

Figure 6.2 illustrates the FT232R 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 FT232R should be programmed to a value of zero

(self-powered).

n order to comply with the first requirement above, the USB bus power (pin 1) is used to control the

RESET# pin of the FT232R device. When the USB host or hub is powered up an internal 1.5kΩ resistor on

USBDP is pulled up to +3.3V (generated using the 4K7 and 10k resistor network), thus identifying the

device as a full speed device to the USB host or hub. When the USB host or hub is powered off, RESET#

will be low and the FT232R is held in reset. Since RESET# is low, the internal 1.5kΩ resistor is not pulled

up to any power supply (hub or host is powered down), so no current flows down USBDP via the 1.5kΩ

pull-up resistor. Failure to do this may cause some USB host or hub controllers to power up erratically.

Figure 6.2 illustrates a self-powered design which has a +4V to +5.25V supply.

Note:

1. When the FT232R is in reset, the UART interface I/O pins are tri-stated. Input pins have internal

200kΩ pull-up resistors to VCCIO, so they will gently pull high unless driven by some external

logic.

2. When using internal FT232R oscillator the VCC supply voltage range must be +4.0V to 5.25V.

3. When using external oscillator the VCC supply voltage range must be +3.3V to 5.25V

Any design which interfaces to +3.3 V or +1.8V would be having a +3.3V or +1.8V supply to

VCCIO.

FT232RL Datasheet(PDF) 20 Page - Future Technology Devices International Ltd.