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| 型号： | MM232R |
| 厂商： | FTDI, Future Technology Devices International Ltd |
| 文件页数： | 16/24页 |
| 文件大小： | 0K |
| 描述： | MOD USB UART MINI DEV FT232R |
| 产品培训模块： | USB Introduction USB-UART Interface Solutions |
| 产品目录绘图： | MM232R |
| 标准包装： | 5 |
| 主要目的： | 接口，USB 2.0 至 UART（RS232/RS422/RS485）电桥 |
| 嵌入式： | 否 |
| 已用 IC / 零件： | FT232R |
| 主要属性： | 全速，300 ~ 3 MB 速率，安全识别号 |
| 次要属性： | 6 ~ 48MHz 时钟发生器输出，免版税驱动器 |
| 已供物品： | 板，连接器 |
| 产品目录页面： | 633 (CN2011-ZH PDF) |
| 相关产品： | 768-1008-6-ND - IC USB FS SERIAL UART 32-QFN 768-1007-6-ND - IC USB FS SERIAL UART 28-SSOP 768-1008-1-ND - IC USB FS SERIAL UART 32-QFN 768-1007-1-ND - IC USB FS SERIAL UART 28-SSOP 768-1008-2-ND - IC USB FS SERIAL UART 32-QFN 768-1007-2-ND - IC USB FS SERIAL UART 28-SSOP |
| 其它名称： | 768-1021 |
Document Reference No.: FT_000214
MM232R USB - Serial UART Development Module Incorporating Clock Generator
Datasheet Version 1.1
Clearance No.: FTDI# 132
6.3 USB Bus Powered with Power Switching Configuration
Figure 6.3 Bus Powered with Power Switching Configuration
USB Bus Powered circuits need to be able to power down in USB suspend mode in order to meet the
<=500μA total USB suspend current requirement (including external logic). Some external can 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 FT232R provides a simple but effective way of turning off power to external circuitry
during USB suspend.
Figure 7.3 shows how to use a discrete P-Channel Logic Level MOSFET to control the power to external logic
circuits. A suitable device would be an International Rectifier ( www.irf.com ) IRLML6402, or equivalent. It is
recommended that a “soft start” circuit consisting of a 1kΩseries resistor and a 0.1μF 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 FT232R, or the USB host / hub controller.
The values used here allow attached circuitry to power up with a slew rate of ~12.5V 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:
i)
ii)
iii)
iv)
The logic to be controlled must have its own reset circuitry so that it will automatically reset itself
when power is applied on coming out of suspend.
Set the Pull-down on Suspend option in the internal EEPROM.
One of the CBUS Pins should be configured as PWE# in the internal EEPROM, and should be used to
switch the power supply to the external circuitry.
For USB high-power bus powered device (one that consumes greater than 100mA, and up to 500mA
of current from the USB bus), the power consumption of the device should be set in the max power
field in the internal EEPROM. A high-power bus powered device must use this descriptor in the
internal EEPROM to inform the system of its power requirements.
v) For 3.3V power controlled circuits the FT232R?s VCCIO pin must not be powered down with the
external circuitry (the PWREN# signal gets its VCC supply from VCCIO). Either connects the power
switch between the output of the 3.3V regulator and the external 3.3V logic or power VCCIO from the
3V3OUT pin of the FT232R.
? Copyright 2010 Future Technology Devices International Ltd
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