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参数资料
| 型号： | FT245RQ-REEL |
| 厂商： | FTDI, Future Technology Devices International Ltd |
| 文件页数： | 17/37页 |
| 文件大小： | 0K |
| 描述： | IC USB TO PARALLEL FIFO 32-QFN |
| 产品培训模块： | USB Introduction |
| 标准包装： | 1 |
| 应用： | USB 至 FIFO 控制器 |
| 接口： | USB，FIFO，（同步/异步） |
| 电源电压： | 1.8 V ~ 5.25 V |
| 封装/外壳： | 32-VFQFN 裸露焊盘 |
| 供应商设备封装： | 32-QFN 裸露焊盘（5x5） |
| 包装： | 标准包装 |
| 安装类型： | 表面贴装 |
| 产品目录页面： | 634 (CN2011-ZH PDF) |
| 配用： | 768-1020-ND - MOD USB PARALLEL FIFO DEV FT245R |
| 其它名称： | 768-1012-6 |
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Copyright 2010 Future Technology Devices International Limited
24
Document No.: FT_000052
FT245R USB FIFO IC Datasheet Version 2.12
Clearance No.: FTDI# 39
7.3 USB Bus Powered with Power Switching Configuration
FT245R
A
G
N
D
G
N
D
G
N
D
G
N
D
T
E
S
T
100nF
3V3OUT
VCCIO
NC
RESET#
NC
+
100nF
10nF
5V VCC
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
+
4.7uF
SHIELD
GND
0.1uF
1k
Soft Start
Circuit
d
g
s
Switched 5V Power
to External Logic
5V VCC
P-Channel Power
MOSFET
10K
5V VCC
Figure 7.3 Bus Powered with Power Switching Configuration
A requirement of USB bus powered applications, is when in USB suspend mode the application draws a
total current of less than 2.5mA. This requirement includes external logic. Some external logic has the
ability to power itself down into a low current state by monitoring the PWREN# signal. For external logic
that cannot power itself down in this way, the FT245R provides a simple but effective method of turning
off power during the USB suspend mode.
Figure 7.3 shows an example of using a discrete P-Channel MOSFET to control the power to external
logic. A suitable device to do this is an International Rectifier (www.irf.com) IRLML6402, or equivalent. It
is recommended that a “soft start” circuit consisting of a 1kΩ series resistor and a 0.1μF capacitor is used
to limit the current surge when the MOSFET turns on. Without the soft start circuit it is possible that the
transient power surge, caused when the MOSFET switches on, will reset the FT245R or the USB host/hub
controller. The soft start circuit example shown in Figure 7.3 powers up with a slew rate of
approximaely12.5V/ms. Thus supply voltage to external logic transitions from GND to +5V in
approximately 400 microseconds.
As an alternative to the MOSFET, a dedicated power switch IC with inbuilt “soft-start” can be used. A
suitable power switch IC for such an application is the Micrel (www.micrel.com) MIC2025-2BM or
equivalent.
With power switching controlled designs the following should be noted:
i) The external logic to which the power is being switched should have its own reset circuitry to
automatically reset the logic when power is re-applied when moving out of suspend mode.
ii) Set the Pull-down on Suspend option in the internal FT245R EEPROM.
iii) The PWREN# pin should be used to switch the power to the external circuitry.
iv) For USB high-power bus powered applications (one that consumes greater than 100mA, and up
to 500mA of current from the USB bus), the power consumption of the application must be set in
the Max Power field in the internal FT245R EEPROM. A high-power bus powered application uses
the descriptor in the internal FT245R EEPROM to inform the system of its power requirements.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| FT245RQ-TRAY | 制造商:Future Technology Devices International (FTDI Chip) 功能描述:Single Chip USB Tray |
| FT24B3 031175 | 制造商:Comair Rotron 功能描述:FAN 120X120X25MM 24VDC |
| FT24B3-E2 | 制造商:Comair Rotron 功能描述:FAN FLIGHT II 120X120X25MM 24V |
| FT24B3-E2 | 制造商:Comair Rotron 功能描述:FAN FLIGHT II 120X120X25 24V |
| FT24C02A | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Two-Wire Serial EEPROM |
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