Copyright © 2015 Future Technology Devices International Limited

25

FT234XD USB TO BASIC UART IC

Version 1.2

Document No.: FT_000753 Clearance No.: FTDI#324

7.3 USB to RS422 Converter

GND

Y

5

Z

6

DI

3

VCC

1

RO

2

A

8

B

7

GND

4

D

R

U2

ZT490E

Q1

IRLML6402

R4

2k

C9

0.1uF

Y

5

Z

6

DI

3

VCC

1

RO

2

A

8

B

7

GND

4

D

R

U3

ZT490E

GND

C8

0.1uF

R6

120R

R7

120R

R5

10k

TxD+

TxD-

RxD+

RxD-

RTS-

RTS+

CTS+

CTS-

GND

VBUS

C4

10nF

C3

0.1uF

C1

4.7uF

GND

GND

FB1

600R/0.5A

VBUS

1

D-

2

D+

3

GND

4

CN1

USB

C5

47pF

C6

47pF

GND

GND

C2

0.1uF

RXD

10

USBDP

12

USBDM

1

3V3OUT

3

RESET#

2

CBUS0

6

TXD

7

CTS#

11

RTS#

8

U1

FT234XD

R1

10k

C7

10nF

GND

GND

TXD

RXD

RTS#

CTS#

PWREN#

R3

27R

R2

27R

Figure 7.3 USB to RS422 Converter Configuration

An example of using the FT234XD as a USB to RS422 converter is shown in Figure 7.3. In this

application, two TTL to RS422 Level Converter ICs are used on the serial UART interface of the FT234XD

to convert the TTL levels of the FT234XD to RS422 levels. There are many suitable level converter

devices available. This example uses Zywyn ZT490E devices. P-Channel MOSFET connected in the VCC

line of ZT490E ensures that USB standby current of 2.5mA is not exceeded.

The ZT490E is specified to transmit and receive data at a rate of up to 10 Mbaud. In this example the

maximum data rate is limited to 3 Mbaud by the FT234XD.