ericmar
Full Member level 5
ft232bm/bl
Hi! May I know wat does the power ctrl do in the circuit? I dont really understand it even after I read thro that section in its datasheet. Can anyone helps me with this?
The notes are as below:
"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 FT232BL provides a simple but effective way of turning off power to external circuitry during USB suspend.
**broken link removed**
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 FT232BL, 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) MIC2025-2BL or equivalent."
In fact, i'm trying to use the ADuM1201 Dual-Channel Digital Isolators to build an Opto-Isolated USB Interface for the USB adapter that i m planning to make. For special purpose, i hv to make the circuit isolated in terms of signal n power (n maybe shield isolation as well).
Wat does the external circuity refer to? Wat is that Soft Start circuit?
Thx 4 any help provided in advanced!
Hi! May I know wat does the power ctrl do in the circuit? I dont really understand it even after I read thro that section in its datasheet. Can anyone helps me with this?
The notes are as below:
"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 FT232BL provides a simple but effective way of turning off power to external circuitry during USB suspend.
**broken link removed**
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 FT232BL, 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) MIC2025-2BL or equivalent."
In fact, i'm trying to use the ADuM1201 Dual-Channel Digital Isolators to build an Opto-Isolated USB Interface for the USB adapter that i m planning to make. For special purpose, i hv to make the circuit isolated in terms of signal n power (n maybe shield isolation as well).
Wat does the external circuity refer to? Wat is that Soft Start circuit?
Thx 4 any help provided in advanced!
