參數(shù)資料
型號： FT245RQ-REEL
廠商： FTDI, Future Technology Devices International Ltd
文件頁數(shù)： 18/37頁
文件大?。?/td> 0K
描述： IC USB TO PARALLEL FIFO 32-QFN
產(chǎn)品培訓模塊： USB Introduction
標準包裝： 1
應用： USB 至 FIFO 控制器
接口： USB，F(xiàn)IFO，（同步/異步）
電源電壓： 1.8 V ~ 5.25 V
封裝/外殼： 32-VFQFN 裸露焊盤
供應商設(shè)備封裝： 32-QFN 裸露焊盤（5x5）
包裝： 標準包裝
安裝類型： 表面貼裝
產(chǎn)品目錄頁面： 634 (CN2011-ZH PDF)
配用： 768-1020-ND - MOD USB PARALLEL FIFO DEV FT245R
其它名稱： 768-1012-6
Copyright 2010 Future Technology Devices International Limited
25
Document No.: FT_000052
FT245R USB FIFO IC Datasheet Version 2.12
Clearance No.: FTDI# 39
v) PWREN# gets its VCC from VCCIO. For designs using 3V3 logic, ensure VCCIO is not powered
down using the external logic. In this case use the +3V3OUT.
7.4 USB Bus Powered with Selectable External Logic Supply
FT245R
A
G
N
D
G
N
D
G
N
D
G
N
D
T
E
S
T
100nF
3V3OUT
VCCIO
NC
RESET#
NC
10nF
D0
D1
D2
D3
D4
D5
D6
D7
TXE#
WR#
RD#
RXF#
USBDP
USBDM
VCC
1
2
3
4
5
OSCI
OSCO
PWREN#
Ferrite
Bead
+
SHIELD
GND
3.3V or 5V Supply
to External Logic
100nF
+
100nF
Vcc
4.7uF
GND
1
Jumper
2
3
Vcc
VCCIO
10k
VCCIO
Figure 7.4 USB Bus Powered with +3.3V or +5V External Logic Power Supply
Figure 7.4 illustrates a USB bus power application with selectable external logic supply. The external logic
can be selected between +3.3V and +5V using the jumper switch. This jumper is used to allow the
FT245R to be interfaced with a +3.3V or +5V logic devices. The VCCIO pin is either supplied with +5V
from the USB bus (jumper pins1 and 2 connected), or from the +3.3V output from the FT245R 3V3OUT
pin (jumper pins 2 and 3 connected). The supply to VCCIO is also used to supply external logic.
With bus powered applications, the following should be noted:
i)
To comply with the 2.5mA current supply limit during USB suspend mode, PWREN# or
SLEEP# signals should be used to power down external logic in this mode. If this is not
possible, use the configuration shown in Section 9.
ii)
The maximum current sourced from the USB bus during normal operation should not exceed
100mA, otherwise a bus powered design with power switching (Section 7.3) should be used.
Another possible configuration could use a discrete low dropout (LDO) regulator which is supplied by the
5V on the USB bus to supply between +1.8V and +2.8V to the VCCIO pin and to the external logic. In
this case VCC would be supplied with the +5V from the USB bus and the VCCIO would be supplied from
the output of the LDO regulator. This results in the FT245R I/O pins driving out at between +1.8V and
+2.8V logic levels.
For a USB bus powered application, it is important to consider the following when selecting the regulator:
i)
The regulator must be capable of sustaining its output voltage with an input voltage of
+4.35V. An Low Drop Out (LDO) regulator should be selected.
ii)
The quiescent current of the regulator must be low enough to meet the total current
requirement of <= 2.5mA during USB suspend mode.
A suitable series of LDO regulators that meets these requirements is the MicroChip/Telcom
(www.microchip.com) TC55 series of devices. These devices can supply up to 250mA current and have a
quiescent current of under 1μA.
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