FTDI FT232BM Usb uart ( usb - serial) i.c. Datasheet

FT232BM USB UART ( USB - Serial) I.C.
The FT232BM is the 2nd generation of FTDI’s popular USB UART I.C. This device not only adds extra functionality
to its FT8U232AM predecessor and reduces external component count, but also maintains a high degree of pin
compatibility with the original, making it easy to upgrade or cost reduce existing designs as well as increasing the
potential for using the device in new application areas.
1.0
Features
HARDWARE FEATURES
•
Single Chip USB Asynchronous Serial Data
VIRTUAL COM PORT (VCP) DRIVERS for
Transfer
-
Windows 98 and Windows 98 SE
•
Full Handshaking & Modem Interface Signals
-
Windows 2000 / ME / Server 2003 / XP
•
UART I/F Supports 7 / 8 Bit Data, 1 / 2 Stop Bits
-
Windows XP 64 Bit
and Odd/Even/Mark/Space/No Parity
-
Windows XP Embedded
•
Data rate 300 => 3M Baud (TTL)
-
Windows CE 4.2
•
Data rate 300 => 1M Baud (RS232)
-
MAC OS-8 and OS-9
•
Data rate 300 => 3M Baud (RS422/RS485)
-
MAC OS-X
•
384 Byte Receive Buffer / 128 Byte Transmit Buffer
-
Linux 2.40 and greater
for high data throughput
D2XX (USB Direct Drivers + DLL S/W Interface)
•
Adjustable RX buffer timeout
-
Windows 98 and Windows 98 SE
•
Fully Assisted Hardware or X-On / X-Off
-
Windows 2000 / ME / Server 2003 / XP
Handshaking
-
Windows XP 64 Bit
In-built support for event characters and line break
-
Windows XP Embedded
condition
-
Windows CE 4.2
•
Auto Transmit Buffer control for RS485
-
Linux 2.40 and greater
•
Support for USB Suspend / Resume through
APPLICATION AREAS
SLEEP# and RI# pins
-
USB RS232 Converters
Support for high power USB Bus powered devices
-
USB  RS422 / RS485 Converters
through PWREN# pin
-
Upgrading RS232 Legacy Peripherals to USB
Integrated level converter on UART and control
-
Cellular and Cordless Phone USB data transfer
•
•
•
signals for interfacing to 5V and 3.3V logic
cables and interfaces
•
Integrated 3.3V regulator for USB IO
-
Interfacing MCU based designs to USB
•
Integrated Power-On-Reset circuit
-
USB Audio and Low Bandwidth Video data transfer
•
Integrated 6MHz – 48Mhz clock multiplier PLL
-
PDA  USB data transfer
•
USB Bulk or Isochronous data transfer modes
-
USB Smart Card Readers
•
4.35V to 5.25V single supply operation
-
Set Top Box (S.T.B.) PC - USB interface
•
UHCI / OHCI / EHCI host controller compatible
-
USB Hardware Modems
•
USB 1.1 and USB 2.0 compatible
-
USB Wireless Modems
•
USB VID, PID, Serial Number and Product
-
USB Instrumentation
Description strings in external EEPROM
-
USB Bar Code Readers
•
EEPROM programmable on-board via USB
•
Compact 32-LD LQFP package
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 1 of 25
FT232BM USB UART ( USB - Serial) I.C.
2.0
Enhancements
This section summarises the enhancements of the 2nd generation device compared to its FT8U232AM predecessor.
For further details, consult the device pin-out description and functional descriptions.
•
Integrated Power-On-Reset (POR) Circuit
This gating is now done on-chip - USBEN has
The device now incorporates an internal POR
now been replaced with the new PWREN# signal
function. The existing RESET# pin is maintained
which can be used to directly drive a transistor or
in order to allow external logic to reset the device
P-Channel MOSFET in applications where power
where required, however for many applications
switching of external circuitry is required. A new
this pin can now simply be hard wired to VCC. In
EEPROM based option makes the device pull
addition, a new reset output pin (RSTOUT#) is
gently down its UART interface lines when the
provided in order to allow the new POR circuit to
power is shut off (PWREN# is High). In this mode,
provide a stable reset to external MCU and other
any residual voltage on external circuitry is bled to
devices. RSTOUT# was the TEST pin on the
GND when power is removed thus ensuring that
previous generation of devices.
external circuitry controlled by PWREN# resets
reliably when power is restored.
•
Integrated RCCLK Circuit
In the previous devices, an external RC circuit
•
•
Lower Suspend Current
was required to ensure that the oscillator and
Integration of RCCLK within the device and internal
clock multiplier PLL frequency was stable prior
design improvements reduce the suspend current
to enabling the clock internal to the device. This
of the FT232BM to under 200uA (excluding the
circuit is now embedded on-chip – the pin assigned
1.5k pull-up on USBDP) in USB suspend mode.
to this function is now designated as the TEST pin
This allows greater margin for peripherals to meet
and should be tied to GND for normal operation.
the USB Suspend current limit of 500uA.
Integrated Level Converter on UART interface
•
Support for USB Isochronous Transfers
and control signals
Whilst USB Bulk transfer is usually the best
The previous devices would drive the UART and
choice for data transfer, the scheduling time of the
control signals at 5V CMOS logic levels. The
data is not guaranteed. For applications where
new device has a separate VCC-IO pin allowing
scheduling latency takes priority over data integrity
the device to directly interface to 3.3V and other
such as transferring audio and low bandwidth
logic families without the need for external level
video data, the new device now offers an option of
converter I.C.’s
USB Isochronous transfer via an option bit in the
EEPROM.
•
Improved Power Management control for USB
Bus Powered, high current devices
The previous devices had a USBEN pin, which
became active when the device was enumerated
by USB. To provide power control, this signal had
to be externally gated with SLEEP# and RESET#.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 2 of 25
FT232BM USB UART ( USB - Serial) I.C.
•
Programmable Receive Buffer Timeout
to the device and they will be sequentially sent to
In the previous device, the receive buffer timeout
the interface at a rate controlled by the prescaler
used to flush remaining data from the receive
setting. As well as allowing the device to be used
buffer was fixed at 16ms timeout. This timeout is
stand-alone as a general purpose IO controller for
now programmable over USB in 1ms increments
example controlling lights, relays and switches,
from 1ms to 255ms, thus allowing the device to
some other interesting possibilities exist. For
be better optimised for protocols requiring faster
instance, it may be possible to connect the device
response times from short data packets.
to an SRAM configurable FPGA as supplied by
vendors such as Altera and Xilinx. The FPGA
•
TXDEN Timing fix
device would normally be un-configured (i.e. have
TXDEN timing has now been fixed to remove the
no defined function) at power-up. Application
external delay that was previously required for
software on the PC could use Bit Bang Mode to
RS485 applications at high baud rates. TXDEN
download configuration data to the FPGA which
now works correctly during a transmit send-break
would define its hardware function, then after the
condition.
FPGA device is configured the FT232BM can
switch back into UART interface mode to allow
•
Relaxed VCC Decoupling
the programmed FPGA device to communicate
The 2 generation devices now incorporate a level
with the PC over USB. This approach allows a
of on-chip VCC decoupling. Though this does
customer to create a “generic” USB peripheral
not eliminate the need for external decoupling
who’s hardware function can be defined under
capacitors, it significantly improves the ease of
control of the application software. The FPGA
PCB design requirements to meet FCC, CE and
based hardware can be easily upgraded or
other EMI related specifications.
totally changed simply by changing the FPGA
nd
configuration data file. Application notes, software
•
Improved PreScaler Granularity
and development modules for this application area
The previous version of the Prescaler supported
will be available from FTDI and other 3rd parties.
division by (n + 0), (n + 0.125), (n + 0.25) and
(n + 0.5) where n is an integer between 2 and
14
•
PreScaler Divide By 1 Fix
16,384 (2 ). To this we have added (n + 0.375),
The previous device had a problem when the
(n + 0.625), (n + 0.75) and (n+ 0.875) which can
integer part of the divisor was set to 1. In the 2nd
be used to improve the accuracy of some baud
generation device setting the prescaler value to 1
rates and generate new baud rates which were
gives a baud rate of 2 million baud and setting it
previously impossible (especially with higher baud
to zero gives a baud rate of 3 million baud. Non-
rates).
integer division is not supported with divisor values
of 0 and 1.
•
Bit Bang Mode
The 2nd generation device has a new option
referred to as “Bit Bang” mode. In Bit Bang mode,
the eight UART interface control lines can be
switched between UART interface mode and an
8-bit Parallel IO port. Data packets can be sent
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 3 of 25
FT232BM USB UART ( USB - Serial) I.C.
•
Less External Support Components
•
Multiple Device Support without EEPROM
As well as eliminating the RCCLK RC network, and
When no EEPROM (or a blank or invalid
for most applications the need for an external reset
EEPROM) is attached to the device, the FT232BM
circuit, we have also eliminated the requirement for
no longer gives a serial number as part of its
a 100K pull-up on EECS to select 6MHz operation.
USB descriptor. This allows multiple devices to
When the FT232BM is being used without the
be simultaneously connected to the same PC.
configuration EEPROM, EECS, EESK and EEDATA
However, we still highly recommend that EEPROM
can now be left n/c. For circuits requiring a long
is used, as without serial numbers a device can
reset time (where the device is reset externally
only be identified by which hub port in the USB tree
using a reset generator I.C., or reset is controlled
it is connected to which can change if the end user
by the IO port of a MCU, FPGA or ASIC device) an
re-plugs the device into a different port.
external transistor circuit is no longer required as the
1.5k pull-up resistor on USBDP can be wired to the
RSTOUT# pin instead of to 3.3V. Note : RSTOUT#
drives out at 3.3V level, not at 5V VCC level. This is
the preferred configuration for new designs.
•
Extended EEPROM Support
The previous generation of devices only supported
EEPROM of type 93C46 (64 x 16 bit). The new
devices will also work with EEPROM type 93C56
(128 x 16 bit) and 93C66 (256 x 16 bit). The extra
space is not used by the device, however it is
available for use by other external MCU / logic whilst
the FT232BM is being held in reset.
•
USB 2.0 (full speed option)
A new EEPROM based option allows the FT232BM
to return a USB 2.0 device descriptor as opposed to
USB 1.1. Note : The device would be a USB 2.0 Full
Speed device (12Mb/s) as opposed to a USB 2.0
High Speed device (480Mb/s).
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 4 of 25
FT232BM USB UART ( USB - Serial) I.C.
3.0
Block Diagram (Simplified)
VCC
PWRCTL
3V3OUT
SLEEP#
PWREN#
3.3 Volt
LDO
Regulator
USBDP
USB
Transceiver
USBDM
48MHz
Baud Rate
Generator
Dual Port TX
Buffer
128 bytes
Serial Interface
Engine
( SIE )
USB
Protocol Engine
UART
FIFO Controller
UART
TXD
RXD
RTS#
CTS#
DTR#
DSR#
DCD#
RI#
TXDEN
TXLED#
RXLED#
Dual Port RX
Buffer
384 Bytes
USB DPLL
3V3OUT
XTOUT
48MHz
6MHZ
Oscillator
x8 Clock
Multiplier
XTIN
12MHz
EECS
EEPROM
Interface
EESK
EEDATA
RESET
GENERATOR
RESET#
RSTOUT#
TEST
GND
3.1
•
•
Functional Block Descriptions
3.3V LDO Regulator
The 3.3V LDO Regulator generates the 3.3 volt
reference voltage for driving the USB transceiver
cell output buffers. It requires an external
decoupling capacitor to be attached to the 3V3OUT
regulator output pin. It also provides 3.3V power to
the RSTOUT# pin. The main function of this block
is to power the USB Transceiver and the Reset
Generator Cells rather than to power external logic.
However, external circuitry requiring 3.3V nominal
at a current of not greater than 5mA could also
draw its power from the 3V3OUT pin if required.
and two single ended receivers provide USB data
in, SEO and USB Reset condition detection.
•
USB DPLL
The USB DPLL cell locks on to the incoming NRZI
USB data and provides separate recovered clock
and data signals to the SIE block.
•
6MHz Oscillator
The 6MHz Oscillator cell generates a 6MHz
reference clock input to the x8 Clock multiplier from
an external 6MHz crystal or ceramic resonator.
USB Transceiver
The USB Transceiver Cell provides the USB 1.1 /
USB 2.0 full-speed physical interface to the USB
cable. The output drivers provide 3.3 volt level slew
rate control signalling, whilst a differential receiver
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 5 of 25
FT232BM USB UART ( USB - Serial) I.C.
•
x8 Clock Multiplier
The x8 Clock Multiplier takes the 6MHz input
from the Oscillator cell and generates a 12MHz
reference clock for the SIE, USB Protocol Engine
and UART FIFO controller blocks. It also generates
a 48MHz reference clock for the USB DPPL and
the Baud Rate Generator blocks.
•
Serial Interface Engine (SIE)
The Serial Interface Engine (SIE) block performs
the Parallel to Serial and Serial to Parallel
conversion of the USB data. In accordance to the
USB 2.0 specification, it performs bit stuffing / unstuffing and CRC5 / CRC16 generation / checking
on the USB data stream.
•
USB Protocol Engine
The USB Protocol Engine manages the data
stream from the device USB control endpoint. It
handles the low level USB protocol (Chapter 9)
requests generated by the USB host controller
and the commands for controlling the functional
parameters of the UART.
•
Dual Port TX Buffer (128 bytes)
Data from the USB data out endpoint is stored
in the Dual Port TX buffer and removed from the
buffer to the UART transmit register under control
of the UART FIFO controller.
•
Dual Port RX Buffer (384 bytes)
Data from the UART receive register is stored in
the Dual Port RX buffer prior to being removed by
the SIE on a USB request for data from the device
data in endpoint.
•
UART FIFO Controller
The UART FIFO controller handles the transfer of
data between the Dual Port RX and TX buffers and
the UART transmit and receive registers.
•
UART
The UART performs asynchronous 7 / 8 bit
Parallel to Serial and Serial to Parallel conversion
DS232B Version 1.8
of the data on the RS232 (RS422 and RS485)
interface. Control signals supported by the UART
include RTS, CTS, DSR , DTR, DCD and RI.
The UART provides a transmitter enable control
signal (TXDEN) to assist with interfacing to
RS485 transceivers. The UART supports RTS/
CTS, DSR/DTR and X-On/X-Off handshaking
options. Handshaking, where required, is handled
in hardware to ensure fast response times. The
UART also supports the RS232 BREAK setting
and detection conditions.
•
Baud Rate Generator
The Baud Rate Generator provides a x16 clock
input to the UART from the 48MHz reference clock
and consists of a 14 bit prescaler and 3 register
bits which provide fine tuning of the baud rate
(used to divide by a number plus a fraction). This
determines the Baud Rate of the UART which is
programmable from 183 baud to 3 million baud.
•
RESET Generator
The Reset Generator Cell provides a reliable
power-on reset to the device internal circuitry
on power up. An additional RESET# input and
RSTOUT# output are provided to allow other
devices to reset the FT232BM or the FT232BM
to reset other devices respectively. During reset,
RSTOUT# is driven low, otherwise it drives out
at the 3.3V provided by the onboard regulator.
RSTOUT# can be used to control the 1.5k
pull-up on USBDP directly where delayed USB
enumeration is required. It can also be used to
reset other devices. RSTOUT# will stay highimpedance for approximately 5ms after VCC
has risen above 3.5V AND the device oscillator is
running AND RESET# is high. RESET# should
be tied to VCC unless it is a requirement to reset
the device from external logic or an external reset
generator i.c.
© Future Technology Devices Intl. Ltd. 2005
Page 6 of 25
FT232BM USB UART ( USB - Serial) I.C.
EEPROM Interface
Though the FT232BM will work without the optional
EEPROM, an external 93C46 (93C56 or 93C66)
EEPROM can be used to customise the USB VID,
PID, Serial Number, Product Description Strings
and Power Descriptor value of the FT232BM for
OEM applications. Other parameters controlled
by the EEPROM include Remote Wake Up,
Isochronous Transfer Mode, Soft Pull Down on
Power-Off and USB 2.0 descriptor modes.
The EEPROM should be a 16 bit wide
configuration such as a MicroChip 93LC46B or
•
4.0
equivalent capable of a 1Mb/s clock rate at VCC =
4.35V to 5.25V. The EEPROM is programmableon board over USB using a utility available from
FTDI’s web site (http://www.ftdichip.com). This
allows a blank part to be soldered onto the PCB
and programmed as part of the manufacturing and
test process.
If no EEPROM is connected (or the EEPROM
is blank), the FT232BM will use its built-in
default VID, PID Product Description and Power
Descriptor Value. In this case, the device will not
have a serial number as part of the USB descriptor.
Device Pin-Out
V
C
C
I
O
V
C
C
TXD
RXD
TXD
VCC
XTIN
AGND
XTOUT
AVCC
TEST
EECS
13
26
3V3OUT
3
30
6
V
C
C
A
V
V
C
8
USBDM
RTS#
CTS#
7
25
32
EESK
FTDI
EEDATA
VCC
3V3OUT
USBDP
CTS#
XXYY
8
4
27
DTR#
16
28
TXDEN
RI#
32
GND
1
2
Figure 1
Pin-Out
(LQFP-32 Package )
RXLED#
XTOUT
23
22
21
20
19
18
16
12
11
EECS
EESK
PWRCTL
EEDATA
PWREN#
TEST
TXDEN
PWREN#
PWRCTL
VCCIO
TXLED#
XTIN
24
A
G
N
D
SLEEP#
G
N
D
14
15
10
G
N
D
17
RXLED#
RI#
9
SLEEP#
RESET#
29
GND
DCD#
TXLED#
DCD#
31
DS232B Version 1.8
RSTOUT#
DSR#
17
9
5
RXD
RTS#
FT232BM
RSTOUT#
USBDM
DSR#
24
1
RESET#
DTR#
USBDP
25
Figure 2
Pin-Out
(Schematic Symbol )
© Future Technology Devices Intl. Ltd. 2005
Page 7 of 25
FT232BM USB UART ( USB - Serial) I.C.
4.1
Signal Descriptions
Table 1 - FT232BM - PINOUT DESCRIPTION
UART INTERFACE GROUP
Pin#
Signal
Type
Description
25
TXD
OUT
Transmit Asynchronous Data Output
24
RXD
IN
Receive Asynchronous Data Input
23
RTS#
OUT
Request To Send Control Output / Handshake signal
22
CTS#
IN
Clear To Send Control Input / Handshake signal
21
DTR#
OUT
Data Terminal Ready Control Output / Handshake signal
20
DSR#
IN
Data Set Ready Control Input / Handshake signal
19
DCD#
IN
Data Carrier Detect Control Input
18
RI#
IN
Ring Indicator Control Input. When the Remote Wakeup option is enabled in the
EEPROM, taking RI# low can be used to resume the PC USB Host controller
from suspend.
16
TXDEN
OUT
Enable Transmit Data for RS485
USB INTERFACE GROUP
Pin#
Signal
Type
Description
7
USBDP
I/O
USB Data Signal Plus ( Requires 1.5k pull-up to 3V3OUT or RSTOUT# )
8
USBDM
I/O
USB Data Signal Minus
EEPROM INTERFACE GROUP
Pin#
Signal
Type
Description
32
EECS
I/O
EEPROM – Chip Select. For 48MHz operation pull EECS to GND using a 10K
resistor. For 6MHz operation no resistor is required. Tri-State during device reset.
**Note 1
1
EESK
OUT
Clock signal to EEPROM. Tri-State during device reset, else drives out. Adding a
10K pull down resistor onto EESK will cause the FT232BM to use USB Product
ID 6004 (hex) instead of 6001 (hex). All of the other USB device descriptors are
unchanged.**Note 1
2
EEDATA
I/O
EEPROM – Data I/O Connect directly to Data-In of the EEPROM and to DataOut of the EEPROM via a 2.2K resistor. Also, pull Data-Out of the EEPROM
to VCC via a 10K resistor for correct operation. Tri-State during device reset.
**Note 1
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 8 of 25
FT232BM USB UART ( USB - Serial) I.C.
POWER CONTROL GROUP
Pin#
Signal
Type
Description
10
SLEEP#
OUT
Goes Low during USB Suspend Mode. Typically used to power-down an external
TTL to RS232 level converter i.c. in USB <=> RS232 converter designs.
15
PWREN#
OUT
Goes Low after the device is configured via USB, then high during USB suspend.
Can be used to control power to external logic using a P-Channel Logic Level
MOSFET switch. Enable the Interface Pull-Down Option in EEPROM when using
the PWREN# pin in this way.
14
PWRCTL
IN
Bus Powered – Tie Low / Self Powered – Tie High (to VCCIO)
MISCELLANEOUS SIGNAL GROUP
Pin#
Signal
Type
Description
4
RESET#
IN
Can be used by an external device to reset the FT232BM. If not required, tie to
VCC.
5
RSTOUT#
OUT
Output of the internal Reset Generator. Stays high impedance for ~ 5ms after
VCC > 3.5V and the internal clock starts up, then clamps its output to the 3.3v
output of the internal regulator. Taking RESET# low will also force RSTOUT# to
drive low. RSTOUT# is NOT affected by a USB Bus Reset.
12
TXLED#
O.C.
LED Drive - Pulses Low when Transmitting Data via USB
11
RXLED#
O.C.
LED Drive - Pulses Low when Receiving Data via USB
27
XTIN
IN
Input to 6MHz Crystal Oscillator Cell. This pin can also be driven by an external
6MHz clock if required. Note : Switching threshold of this pin is VCC/2, so if
driving from an external source, the source must be driving at 5V CMOS level or
a.c. coupled to centre around VCC/2.
28
XTOUT
OUT
Output from 6MHz Crystal Oscillator Cell. XTOUT stops oscillating during USB
suspend, so take care if using this signal to clock external logic.
31
TEST
IN
Puts device in I.C. test mode – must be tied to GND for normal operation.
POWER AND GND GROUP
Pin#
Signal
Type
Description
6
3V3OUT
OUT
3.3 volt Output from the integrated L.D.O. regulator This pin should be decoupled
to GND using a 33nF ceramic capacitor in close proximity to the device pin. Its
prime purpose is to provide the internal 3.3V supply to the USB transceiver cell
and the RSTOUT# pin. A small amount of current (<= 5mA) can be drawn from
this pin to power external 3.3v logic if required.
3,26
VCC
PWR
+4.35 volt to +5.25 volt VCC to the device core, LDO and non-UART interface
pins.
13
VCCIO
PWR
+3.0 volt to +5.25 volt VCC to the UART interface pins 10..12, 14..16 and 18..25.
When interfacing with 3.3V external logic in a bus powered design connect
VCCIO to a 3.3V supply generated from the USB bus. When interfacing with
3.3V external logic in a self powered design connect VCCIO to the 3.3V supply
of the external logic. Otherwise connect to VCC to drive out at 5V CMOS level.
9,17
GND
PWR
Device - Ground Supply Pins
30
AVCC
PWR
Device - Analog Power Supply for the internal x8 clock multiplier
29
AGND
PWR
Device - Analog Ground Supply for the internal x8 clock multiplier
**Note 1 - During device reset, these pins are tri-state but pulled up to VCC via internal 200K resistors.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 9 of 25
FT232BM USB UART ( USB - Serial) I.C.
5.0 Package Outline
Figure 3 – 32 LD LQFP Package Dimensions
9
7
32
Pin # 1
FTDI
FT232BM
XXYY
7
9
0.8
1
+/-
0.05 Min
0.15 Max
0.37 +/- 0.07
1o
1.4 +/- 0.05
1.60 MAX
12o
0.09 Min
0.16 Max
0.09 Min
0.2 Max
0.25
0.35 +/- 0.05
0.2 Min
0.6 +/- 0.15
The FT232BM is supplied in a 32 pin LQFP package as standard. This package has a 7mm x 7mm body ( 9mm x
9mm including leads ) with leads on a 0.8mm pitch. The above drawing shows the LQFP-32 package – all dimensions
are in millimetres. Note that there are two date code formats used - XXYY = Date Code where XX = 2 digit year
number, YY = 2 digit week number; or XYY-N where X = 1 digit year. number, YY = 2 digit week number, and -N is a
integer.
A lead free version is available, part number FT232BL.
An alternative 5mm x 5mm leadless QFN32 package is also available for projects where package area is critical. Part
number for this version is FT232BQ. The FT232BQ is also a lead free package. See their seperate datasheets for
package dimensions.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 10 of 25
6.0
FT232BM USB UART ( USB - Serial) I.C.
Absolute Maximum Ratings
These are the absolute maximum ratings for the FT232BM device in accordance with the Absolute Maximum Rating System
(IEC 60134). Exceeding these may cause permanent damage to the device.
Parameter
Value
Storage Temperature
Units
–65 C to + 150 C
o
Floor Life (Out of Bag) at Factory Ambient
(30oC/60% Relative Humidity)
Degrees C
o
192 Hours (Level 3 Compliant)
**Note 2
Ambient Temperature (Power Applied)
0oC to + 70oC
M.T.B.F. (at 35 C)
Degrees C
247484 Hours ≈ 28 Years
o
VCC Supply Voltage
-0.5 to +6.00
V
D.C. Input Voltage - USBDP and USBDM
-0.5 to +3.8
V
D.C. Input Voltage - High Impedance Bidirectionals
-0.5 to +(Vcc +0.5)
V
D.C. Input Voltage - All other Inputs
-0.5 to +(Vcc +0.5)
V
24
mA
DC Output Current – Outputs
DC Output Current – Low Impedance Bidirectionals
24
mA
Power Dissipation (VCC = 5.25V)
500
mW
+/- 3000
V
+/-200
mA
Electrostatic Discharge Voltage (Human Body Model) (I < 1uA)
Latch Up Current (Vi = +/- 10V maximum, for 10 ms)
**Note 2 – If devices are stored out of the packaging beyond this time limit the devices should be baked before use.
The devices should be ramped up to a temperature of 110oC and baked for 8 to 10 hours.
6.1
D.C. Characteristics
DC Characteristics ( Ambient Temperature = 0 to 70oC )
Operating Voltage and Current
Parameter
Description
Min
Typ
Max
Units
Conditions
Vcc1
VCC Operating Supply Voltage
4.35
5.0
5.25
V
Vcc2
VCCIO Operating Supply Voltage
3.0
-
5.25
V
Icc1
Operating Supply Current
-
25
-
mA
Normal Operation
Icc2
Operating Supply Current
-
180
200
uA
USB Suspend **Note 3
**Note 3 – Supply current excludes the 200uA nominal drawn by the external pull-up resistor on USBDP.
UART IO Pin Characteristics ( VCCIO = 5.0V )
Parameter
Description
Min
Typ
Max
Units
Voh
Output Voltage High
3.2
4.1
4.9
V
I source = 2mA
Vol
Output Voltage Low
0.3
0.4
0.6
V
I sink = 2mA
Vin
Input Switching Threshold
1.3
1.6
1.9
V
**Note 4
VHys
Input Switching Hysteresis
50
55
60
mV
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Conditions
Page 11 of 25
FT232BM USB UART ( USB - Serial) I.C.
UART IO Pin Characteristics ( VCCIO = 3.0 - 3.6V )
Parameter
Description
Min
Typ
Max
Units
Conditions
Voh
Output Voltage High
2.2
2.7
3.2
V
I source = 1mA
Vol
Output Voltage Low
0.3
0.4
0.5
V
I sink = 2 mA
Vin
Input Switching Threshold
1.0
1.2
1.5
V
**Note 4
VHys
Input Switching Hysteresis
20
25
30
mV
**Note 4 – Inputs have an internal 200K pull-up resistor to VCCIO.
XTIN / XTOUT Pin Characteristics
Parameter
Description
Min
Typ
Max
Units
Conditions
Voh
Output Voltage High
4.0
-
5.0
V
Fosc = 6MHz
Vol
Output Voltage Low
0.1
-
1.0
V
Fosc = 6MHz
Vin
Input Switching Threshold
1.8
2.5
3.2
V
RESET#, TEST, EECS, EESK, EEDATA Pin Characteristics
Parameter
Description
Min
Typ
Max
Units
Conditions
Voh
Output Voltage High
3.2
4.1
4.9
V
I source = 2mA
Vol
Output Voltage Low
0.3
0.4
0.6
V
I sink = 2 mA
Vin
Input Switching Threshold
1.3
1.6
1.9
V
**Note 5
VHys
Input Switching Hysteresis
50
55
60
mV
**Note 5 – EECS, EESK and EEDATA pins have an internal 200K pull-up resistor to VCC
RSTOUT Pin Characteristics
Parameter
Description
Min
Typ
Max
Units
Conditions
Voh
Output Voltage High
3.0
-
3.6
V
I source = 2mA
Vol
Output Voltage Low
0.3
-
0.6
V
I sink = 2mA
Typ
Max
Units
USB IO Pin Characteristics
Parameter
Description
Min
Conditions
UVoh
IO Pins Static Output ( High)
2.8
3.6
V
RI = 1.5K to 3V3Out ( D+ )
RI = 15K to GND ( D- )
UVol
IO Pins Static Output ( Low )
0
0.3
V
RI = 1.5K to 3V3Out ( D+ )
RI = 15K to GND ( D- )
UVse
Single Ended Rx Threshold
0.8
2.0
V
UCom
Differential Common Mode
0.8
2.5
V
UVDif
Differential Input Sensitivity
0.2
UDrvZ
Driver Output Impedance
29
V
44
Ohm
**Note 5
**Note 5 – Driver Output Impedance includes the external 27R series resistors on USBDP and USBDM pins.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 12 of 25
FT232BM USB UART ( USB - Serial) I.C.
7.0
Device Configuration Examples
7.1
Oscillator Configurations
Figure 5
Crystal or 2-Pin Ceramic Resonator
Configuration
Figure 4
3-Pin Ceramic Resonator
Configuration
FT223BM
FT232BM
27pF
27
3-Pin Resonator
6MHz
XTIN
27
XTIN
28
XTOUT
2 - Pin Resonator
or Crystal
6MHz
1M
27pF
28
XTOUT
Figure 4 illustrates how to use the FT232BM with a 3-Pin Ceramic Resonator. A suitable part would be a ceramic
resonator from Murata’s CERALOCK range. (Murata Part Number CSTCR6M00G15), or equivalent. 3-Pin ceramic
resonators have the load capacitors built into the resonator so no external loading capacitors are required. This
makes for an economical configuration. The accuracy of this Murata ceramic resonator is +/- 0.1% and it is specifically
designed for USB full speed applications. A 1 MegaOhm loading resistor across XTIN and XTOUT is recommended in
order to guarantee this level of accuracy.
Other ceramic resonators with a lesser degree of accuracy (typically +/- 0.5%) are technically out-with the USB
specification, but it has been calculated that using such a device will work satisfactorily in practice with a FT232BM
design.
Figure 5 illustrates how to use the FT232BM with a 6MHz Crystal or 2-Pin Ceramic Resonator. In this case, these
devices do not have in-built loading capacitors so these have to be added between XTIN, XTOUT and GND as
shown. A value of 27pF is shown as the capacitor in the example – this will be good for many crystals and some
resonators but do select the value based on the manufacturers recommendations wherever possible. If using a crystal,
use a parallel cut type. If using a resonator, see the previous note on frequency accuracy.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 13 of 25
FT232BM USB UART ( USB - Serial) I.C.
7.2
EEPROM Configuration
Figure 6
EEPROM Configuration
FT232BM
32
EECS
1
EESK
2
EEDATA
VCC
EEPROM - 93C46 / 56 / 66
1
2
2k2
3
4
10k
CS
VCC
SK
NC
DIN
NC
DOUT
GND
VCC
8
7
6
5
Figure 6 illustrates how to connect the FT232BM to the
93C46 (93C56 or 93C66) EEPROM. EECS (pin 32) is directly
connected to the chip select (CS) pin of the EEPROM. EESK
(pin 1) is directly connected to the clock (SK) pin of the
EEPROM. EEDATA (pin 2) is directly connected to the Data
In (Din) pin of the EEPROM. There is a potential condition
whereby both the Data Output (Dout) of the EEPROM
can drive out at the same time as the EEDATA pin of the
FT232BM. To prevent potential data clash in this situation,
the Dout of the EEPROM is connected to EEDATA of the
FT232BM via a 2.2K resistor.
Following a power-on reset or a USB reset, the FT232BM will
scan the EEPROM to find out (a) if an EEPROM is attached
to the Device and (b) if the data in the device is valid. If both
of these are the case, then the FT232BM will use the data in
the EEPROM, otherwise it will use its built-in default values.
When a valid command is issued to the EEPROM from the
FT232BM, the EEPROM will acknowledge the command by
pulling its Dout pin low. In order to check for this condition,
it is necessary to pull Dout high using a 10K resistor. If the
command acknowledge doesn’t happen then EEDATA will be pulled high by the 10K resistor during this part of the
cycle and the device will detect an invalid command or no EEPROM present.
There are two varieties of these EEPROM’s on the market – one is configured as being 16 bits wide, the other is
configured as being 8 bits wide. These are available from many sources such as Microchip, STMicro, ISSI etc. The
FT232BM requires EEPROM’s with a 16-bit wide configuration such as the Microchip 93LC46B device. The EEPROM
must be capable of reading data at a 1Mb clock rate at a supply voltage of 4.35V to 5.25V. Most available parts are
capable of this.
Check the manufacturers data sheet to find out how to connect pins 6 and 7 of the EEPROM. Some devices specify
these as no-connect, others use them for selecting 8 / 16 bit mode or for test functions. Some other parts have their
pinout rotated by 90o so please select the required part and its options carefully.
It is possible to “share” the EEPROM between the FT232BM and another external device such as an MCU. However,
this can only be done when the FT232BM is in its reset condition as it tri-states its EEPROM interface at that time. A
typical configuration would use four bit’s of an MCU IO Port. One bit would be used to hold the FT232BM reset (using
RESET#) on power-up, the other three would connect to the EECS, EESK and EEDATA pins of the FT232BM in
order to read / write data to the EEPROM at this time. Once the MCU has read / written the EEPROM, it would take
RESET# high to allow the FT232BM to configure itself and enumerate over USB.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 14 of 25
7.3
FT232BM USB UART ( USB - Serial) I.C.
USB Bus Powered and Self Powered Configuration
Figure 7
USB Bus Powered Configuration
Figure 7 illustrates a typical USB bus powered configuration. A USB Bus Powered device gets its power from the USB
USB "B"
Connector
Ferrite Bead
470R
VCC
1
2
27R
3
4
3
FT232BM
27R
6
10nF
33nF
8
7
26
V
C
C
30
13
V
C
C
3v3OUT
V
C
C
I
O
0.1uF
A
V
C
C
USB DM
USB DP
1k5
5
VCC
4
VCC
14
RSTOUT#
RESET#
POWERCTL
+
0.1uF
0.1uF
10uF
G
N
D
A
G
N
D
G
N
D
9
17
29
Decoupling Capacitors
bus. Basic rules for USB Bus power devices are as follows –
a) On plug-in, the device must draw no more than 100mA
b) On USB Suspend the device must draw no more than 500uA.
c) A Bus Powered High Power Device (one that draws more than 100mA) should use the PWREN# pin to keep the
current below 100mA on plug-in and 500uA on USB suspend.
d) A device that consumes more than 100mA can not be plugged into a USB Bus Powered Hub
e) No device can draw more that 500mA from the USB Bus.
PWRCTL (pin 14) is pulled low to tell the device to use a USB Bus Power descriptor. The power descriptor in the
EEPROM should be programmed to match the current draw of the device.
A Ferrite Bead is connected in series with USB power to prevent noise from the device and associated circuitry (EMI)
being radiated down the USB cable to the Host. The value of the Ferrite Bead depends on the total current required by
the circuit – a suitable range of Ferrite Beads is available from Steward (www.steward.com) for example Steward Part
# MI0805K400R-00 also available as DigiKey Part # 240-1035-1.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 15 of 25
Figure 8
USB Self Powered Configuration
USB "B"
Connector
FT232BM USB UART ( USB - Serial) I.C.
470R
VCC
1
2
27R
3
4
3
FT232BM
27R
6
33nF
26
V
C
C
30
13
V
C
C
3v3OUT
V
C
C
I
O
0.1uF
A
V
C
C
4k7
8
7
10k
USB DM
USB DP
1k5
5
4
VCC
VCC
14
RSTOUT#
RESET#
POWERCTL
+
0.1uF
0.1uF
10uF
G
N
D
A
G
N
D
G
N
D
9
17
29
Decoupling Capacitors
Figure 8 illustrates a typical USB self powered configuration. A USB Self Powered device gets its power from its own
POWER SUPPLY and does not draw current from the USB bus. The basic rules for USB Self power devices are as
follows –
a) A Self-Powered device should not force current down the USB bus when the USB Host or Hub Controller is
powered down.
b) A Self Powered Device can take as much current as it likes during normal operation and USB suspend as it has its
own POWER SUPPLY.
c) A Self Powered Device can be used with any USB Host and both Bus and Self Powered USB Hubs
PWRCTL (pin 14) is pulled high to tell the device to use a USB Bus Power descriptor. The power descriptor in the
EEPROM should be programmed to a value of zero. The USB power descriptor option in the EEPROM should be
programmed to a value of zero (self powered).
To meet requirement a) the 1.5K pull-up resistor on USBDP is connected to RSTOUT# as per the bus-power circuit.
However, the USB Bus Power is used to control the RESET# Pin of the FT232BM device. When the USB Host or
Hub is powered up RSTOUT# will pull the 1.5K resistor on USBDP to 3.3V, thus identifying the device as a full speed
device to USB. When the USB Host or Hub power is off, RESET# will go low and the device will be held in reset. As
RESET# is low, RSTOUT# will also be low, so no current will be forced down USBDP via the 1.5K pull-up resistor
when the host or hub is powered down. Failure to do this may cause some USB host or hub controllers to power up
erratically.
Note : When the FT232BM is in reset, the UART interface pins all go tri-state. These pins have internal 200K pull-up
resistors to VCCIO, so they will gently pull high unless driven by some external logic.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 16 of 25
7.4
FT232BM USB UART ( USB - Serial) I.C.
UART Interface Configuration
Figure 9
USB <=> RS232 Converter Configuration
FT232BM
PWREN#
SLEEP#
TXD
RXD
RTS#
CTS#
DTR#
DSR#
DCD#
RI#
TXDEN
VCC
15
SP213EHCA
10
25
25
7
24
22
23
20
22
8
21
6
20
5
19
26
18
19
16
21
12
SHDN#
T1In
T1Out
R4Out
R4In
T3In
T3Out
R1Out
R1In
T2In
DB9-M
11
EN
T2Out
R2Out
R2In
R3Out
R3In
R5Out
R5In
T4In
T4Out
C1+
C2+
2
3
23
2
1
7
9
8
3
4
4
6
27
1
16
9
28
5
TXD
RXD
RTS
CTS
DTR
DSR
DCD
RI
GND
15
0.1uF
0.1uF
14
17
C1-
C2-
V-
V+
0.1uF
G
N
D
16
13
0.1uF
V
C
C
VCC
11
10
0.1uF
VCC
Figure 9 illustrates how to connect the UART interface of the FT232BM to a TTL – RS232 Level Converter I.C. to
make a USB <=> RS232 converter using the popular “213” series of TTL to RS232 level converters. These devices
have 4 transmitters and 5 receivers in a 28 LD SSOP package and feature an in-built voltage converter to convert the
5v (nominal) VCC to the +/- 9 volts required by RS232. An important feature of these devices is the SHDN# pin which
can power down the device to a low quiescent current during USB suspend mode
The device used in the example is a Sipex SP213EHCA which is capable of RS232 communication at up to 500K
baud. If a lower baud rate is acceptable, then several pin compatible alternatives are available such as Sipex
SP213ECA , Maxim MAX213CAI and Analog Devices ADM213E which are good for communication at up to 115,200
baud. If a higher baud rate is desired, use a Maxim MAX3245CAI part which is capable of RS232 communication at
rates of up to 1M baud. The MAX3245 is not pin compatible with the 213 series devices, also its SHDN pin is active
high so connect this to PWREN# instead of SLEEP#.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 17 of 25
FT232BM USB UART ( USB - Serial) I.C.
Figure 10
USB <=> RS422 Converter Configuration
VCC
14 SP491
FT232BM
PWREN#
SLEEP#
TXD
RXD
RTS#
CTS#
DTR#
DSR#
DCD#
RI#
TXDEN
15
4
10
5
25
24
D
TXDM
9
TXDP
RXDP
11
2
R
6
22
21
4
20
5
12
120R
7
RXDM
VCC
14 SP491
GND
10
D
RTSM
9
RTSP
CTSP
3
11
2
R
18
16
10
3
23
19
DB9-M
6
12
7
120R
CTSM
Figure 10 illustrates how to connect the UART interface of the FT232BM to a TTL – RS422 Level Converter I.C. to
make a USB <=> RS422 converter. There are many such level converter devices available – this example uses Sipex
SP491 devices which have enables on both the transmitter and receiver. Because the transmitter enable is active
high, it is connected to the SLEEP# pin. The receiver enable is active low and is connected to the PWREN# pin. This
ensures that both the transmitters and receivers are enabled when the device is active, and disabled when the device
is in USB suspend mode. If the design is USB BUS powered, it may be necessary to use a P-Channel logic level
MOSFET (controlled by PWREN#) in the VCC line of the SP491 devices to ensure that the USB standby current of
500uA is met.
The SP491 is good for sending and receiving data at a rate of up to 5M Baud – in this case the maximum rate is
limited to 3M Baud by the FT232BM.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 18 of 25
Figure 11
USB <=> RS485 Converter Configuration
FT232BM USB UART ( USB - Serial) I.C.
FT232BM
PWREN#
SLEEP#
TXD
RXD
RTS#
CTS#
DTR#
DSR#
DCD#
RI#
TXDEN
DB9-M
15
10
VCC
SP481
8
3
7
25
4
24
2
23
22
1
D
6
R
DM
DP
GND
5
120R
21
20
LINK
19
18
16
Figure 11 illustrates how to connect the UART interface of the FT232BM to a TTL – RS485 Level Converter I.C. to
make a USB => RS485 converter. This example uses the Sipex SP481 device but there are similar parts available
from Maxim and Analog Devices amongst others. The SP481 is a RS485 device in a compact 8 pin SOP package.
It has separate enables on both the transmitter and receiver. With RS485, the transmitter is only enabled when a
character is being transmitted from the UART. The TXDEN pin on the FT232BM is provided for exactly that purpose
and so the transmitter enable is wired to TXDEN. The receiver enable is active low, so it is wired to the PWREN# pin
to disable the receiver when in USB suspend mode.
RS485 is a multi-drop network – i.e. many devices can communicate with each other over a single two wire cable
connection. The RS485 cable requires to be terminated at each end of the cable. A link is provided to allow the cable
to be terminated if the device is physically positioned at either end of the cable.
In this example the data transmitted by the FT232BM is also received by the device that is transmitting. This is a
common feature of RS485 and requires the application software to remove the transmitted data from the received
data stream. With the FT232BM it is possible to do this entirely in hardware – simply modify the schematic so that
RXD of the FT232BM is the logical OR of the SP481 receiver output with TXDEN using an HC32 or similar logic gate.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 19 of 25
FT232BM USB UART ( USB - Serial) I.C.
7.5 LED Interface
Figure 12
Dual LED Configuration
Figure 13
Single LED Configuration
VCCIO
TX
RX
220R
220R
RXLED#
LED
220R
FT232BM
FT232BM
TXLED#
VCCIO
12
TXLED#
11
RXLED#
12
11
The FT232BM has two IO pins dedicated to controlling LED status indicators, one for transmitted data the other
for received data. When data is being transmitted / received the respective pins drive from tri-state to low in order
to provide indication on the LEDs of data transfer. A digital one-shot timer is used so that even a small percentage
of data transfer is visible to the end user. Figure 12 shows a configuration using two individual LED’s – one for
transmitted data the other for received data. In Figure 13, the transmit and receive LED indicators are wire-OR’ed
together to give a single LED indicator which indicates any transmit or receive data activity.
Another possibility (not shown here) is to use a 3 pin common anode tri-color LED based on the circuit in Figure 13 to
have a single LED that can display activity in a variety of colors depending on the ratio of transmit activity compared to
receive activity.
Note that the LED’s are connected to VCCIO.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 20 of 25
FT232BM USB UART ( USB - Serial) I.C.
7.6 Interfacing to 3.3v Logic
Figure 14
Bus Powered Circuit with 3.3V logic drive / supply voltage
3.3v LDO Regulator
In
3.3v Power to External
Logic
Out
Gnd
0.1uF
USB "B"
Connector
Ferrite Bead
1
470R
VCC
27R
2
3
3
V
C
C
27R
4
10nF
26
6
33nF
13
V
C
C
V
C
C
I
O
3v3OUT
30
0.1uF
A
V
C
C
FT232BM
8
7
USB DM
USB DP
Figure 14 shows how to configure the FT232BM to interface with a 3.3V logic device. In this example, a discrete
3.3V regulator is used to supply the 3.3V logic from the USB supply. VCCIO is connected to the output of the 3.3V
regulator, which in turn will cause the UART interface IO pins to drive out at 3.3V level. For USB bus powered circuits
some considerations have to be taken into account when selecting the regulator –
a) The regulator must be capable of sustaining its output voltage with an input voltage of 4.35 volts. A Low Drop Out
(LDO) regulator must be selected.
b) The quiescent current of the regulator must be low in order to meet the USB suspend total current requirement of
<= 500uA during USB suspend.
An example of a regulator family that meets these requirements is the MicroChip (Telcom) TC55 Series. These
devices can supply up to 250mA current and have a quiescent current of under 1uA.
In some cases, where only a small amount of current is required (< 5mA) , it may be possible to use the in-built
regulator of the FT232BM to supply the 3.3v without any other components being required. In this case, connect
VCCIO to the 3v3OUT pin of the FT232BM.
Note : It should be emphasised that the 3.3V supply for VCCIO in a bus powered design with a 3.3V logic interface
should come from an LDO which is supplied by the USB bus, or from the 3V3OUT pin of the FT232BM, and not from
any other source.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 21 of 25
FT232BM USB UART ( USB - Serial) I.C.
Figure 15
Self Powered Circuit with 3.3V logic drive / supply voltage
VCC3V
USB "B"
Connector
470R
1
27R
2
3
4
0.1uF
27R
33nF
3
30
26
V
C
C
A
V
C
6
C
3v3OUT
13
V
C
C
V
C
C
I
O
FT232BM
4K7
8
7
10K
USB DM
USB DP
VCC3V
1K5
5
4
VCC5V
0.1uF
PWRCTL
RSTOUT#
RESET#
+
0.1uF
VCC5V
10uF
G
N
D
A
G
N
D
G
N
D
9
14
17
29
Decoupling Capacitors
Figure 15 is an example of a USB self powered design with 3.3V interface. In this case VCCIO is supplied by an
external 3.3V supply in order to make the device IO pins drive out at 3.3V logic level, thus allowing it to be connected
to a 3.3V MCU or other external logic. A USB self powered design uses its own power supplies, and does not draw
any of its power from the USB bus. In such cases, no special care need be taken to meet the USB suspend current
(0.5 mA) as the device does not get its power from the USB port.
As with bus powered 3.3V interface designs, in some cases, where only a small amount of current is required (<5mA),
it may be possible to use the in-built regulator of the FT232BM to supply the 3.3V without any other components being
required. In this case, connect VCCIO to the 3v3OUT pin of the FT232BM.
Note that in this case PWRCTL is pulled up to VCCIO, not VCC.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 22 of 25
FT232BM USB UART ( USB - Serial) I.C.
7.7 Power Switching
Figure 16
Bus Powered Circuit ( <= 100mA ) with Power Control
P-Channel Power
MOSFET
s
Switched 5v Power to
External Logic
d
0.1uF
0.1uF
Soft Start
Circuit
1K
g
USB "B"
Connector
Ferrite Bead
1
2
3
470R
VCC
27R
3
V
C
C
27R
4
10nF
26
6
33nF
13
V
C
C
3v3OUT
V
C
C
I
O
30
0.1uF
A
V
C
C
FT232BM
8
7
USB DM
PWREN#
15
USB DP
USB Bus powered circuits need to be able to power down in USB suspend mode in order to meet the <= 500uA total
suspend current requirement (including external logic). Some external logic can power itself down into a low current
state by monitoring the PWREN# pin. For external logic that cannot power itself down in that way, the FT232BM
provides a simple but effective way of turning off power to external circuitry during USB suspend.
Figure 16 shows how to use a discrete P-Channel Logic Level MOSFET to control the power to external logic
circuits. A suitable device could be a Fairchild NDT456P, or International Rectifier IRLML6402, or equivalent. It is
recommended that a “soft start” circuit consisting of a 1K series resistor and a 0.1 uF capacitor are used to limit the
current surge when the MOSFET turns on. Without the soft start circuit there is a danger that the transient power
surge of the MOSFET turning on will reset the FT232BM, or the USB host / hub controller. The values used here
allow attached circuitry to power up with a slew rate of ~12.5 V per millisecond, in other words the output voltage will
transition from GND to 5V in approximately 400 microseconds.
Alternatively, a dedicated power switch i.c. with inbuilt “soft-start” can be used instead of a MOSFET. A suitable power
switch I.C. for such an application would be a Micrel (www.micrel.com) MIC2025-2BM or equivalent.
Please note the following points in connection with power controlled designs –
a) The logic to be controlled must have its own reset circuitry so that it will automatically reset itself when power is reapplied on coming out of suspend.
b) Set the Pull-down on Suspend option in the FT232BM’s EEPROM.
c) For USB high-power bus powered device (one that consumes greater than 100 mA, and up to 500 mA of current
from the USB bus), the power consumption of the device should be set in the max power field in the EEPROM.
A high-power bus powered device must use this descriptor in the EEPROM to inform the system of its power
requirements.
d) For 3.3V power controlled circuits VCCIO must not be powered down with the external circuitry (PWREN# gets
its VCC supply from VCCIO). Either connect the power switch between the output of the 3.3V regulator and the
external 3.3V logic OR if appropriate power VCCIO from the 3V3OUT pin of the FT232BM.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
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FT232BM USB UART ( USB - Serial) I.C.
8.0 Document Revision History
DS232B Version 1.0 – Initial document created 30 April 2002.
DS232B Version 1.1 –
Updated 04 August 2002
•
Section 4.1 RESET# Pin description corrected (RESET# does not have an internal 200k pull-up to VCC as previously stated).
•
Figure 2 pin-out corrected (EECS = Pin 32).
DS232B Version 1.2 –
Updated 27 October 2003
•
Pin and package naming made consistent throughout data sheet.
•
Section 1.0 Updated to reflect availability of Mac OS X driver.
•
Section 2.0 Minor corrections.
•
Section 3.1 Minor changes to functional block descriptions of SIE, RESET Generator, and EEPROM interface.
•
Section 4.1 Note added to EEPROM interface group.
•
Section 4.1 RSTOUT# Pin description amended.
•
Section 6.1 Minimum operating supply voltage adjusted.
•
Section 6.1 EESK added to Note 3.
•
Section 6.1 UART IO pin characteristics amended.
•
Section 6.1 RESET#, TEST, EECS, EESK, and EEDATA pin characteristics amended.
•
Section 6.1 RSTOUT pin characteristics amended.
•
Section 7.1 Updated recommended ceramic resonator part number and circuit configuration.
•
Section 7.3 “USB Self Powered Configuration (1)” (original figure 8 removed). Recommended circuit for USB self powered designs updated. Subsequent figure numbers have changed as a
result.
•
Section 7.6 Note added to description of Bus powered circuit with 3.3V logic drive / supply voltage.
•
Section 7.6 Self Powered Circuit with 3.3V logic drive / supply voltage added (new figure 16).
DS232B Version 1.3 –
Updated 10 December 2003
•
Section 5.0 Package drawing amended
•
Section 6.0 Floor Life / Relative Humidity specification added. ESD and Latch Up specifications amended.
•
Section 7.1 Required resonator / crystal accuracy corrected.
DS232B Version 1.4 –
Updated 10 February 2004
•
Grammar Correcttions
•
Section 10.0 FTDI Address Updated
•
Section 2.0 Extended EEPROM Support corrected
•
Section 4.1 VCCIO Pin description amended.
•
Section 7.4 RS485 Example Sipex SP481 part number corrected.
DS232B Version 1.5 –
Updated April 2004
•
Section 4.1 EESK Pin Description amended.
•
Section 7.6 Figure 16 PWRCTL Pin number corrected.
•
Section 7.7 Figure 15 PWREN# Pin number corrected.
DS232B Version 1.6 –
Updated November 2004
•
Section 1.0 WinCE drivers now available.
•
Section 5.0 Date code format updated.
•
Section 6.0 Absolute Maximum Ratings table reformated.
DS232B Version 1.7 –
Updated February 2005
•
Section 1.0 D2XX drivers for Linux and Windows CE now available.
•
Section 5.0 FT232BL (lead Free) and FT232BQ (lead free QFN package) now available.
DS232B Version 1.8 –
Updated December 2005
•
Section 6.1 USB dataline Input voltage absolute maximum voltage added.
•
Section 1.0 Driver OS support updated.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 24 of 25
FT232BM USB UART ( USB - Serial) I.C.
9.0 Disclaimer
© Future Technology Devices International Limited , 2005
Neither the whole nor any part of the information contained in, or the product described in this manual, may be
adapted or reproduced in any material or electronic form without the prior written consent of the copyright holder.
This product and its documentation are supplied on an as-is basis and no warranty as to their suitability for any
particular purpose is either made or implied.
Future Technology Devices International Ltd. will not accept any claim for damages howsoever arising as a result of
use or failure of this product. Your statutory rights are not affected.
This product or any variant of it is not intended for use in any medical appliance, device or system in which the failure
of the product might reasonably be expected to result in personal injury.
This document provides preliminary information that may be subject to change without notice.
10.0 Contact Information
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DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 25 of 25