- Silicon Labs Community
- Welcome and Announcements
- Silicon Labs Knowledge Base
- 8-bit MCU
- 32-bit MCU
- Bluetooth / Wi-Fi
- Other Products Category
- Optical/RH/Temp Sensor
- Other Products
- Hardware and Software Tools
- Simplicity Studio and Software
- General Discussions and Suggestions
- Chinese Forum
- Software Libraries
- Development Kits
- Reference Designs
- Third Party Tools
- White Papers
- Official Blog of Silicon Labs
- Chinese Blog
08-31-2017 07:43 AM
I've seen posts here about power options but they do not cover my issue.
I've got a system where I can't provide a valid VBUS from the USB connector (because I do not have a standard one). I just have D+,D-,GND and a common power source for all my circutry.
In the datasheet it is said that the detection input threshold of the VBUS is 2.5V. Can I simply connect VBUS and all other power pins of the CP2105 to my common power source (3.3V)?
Am I correct assuming that after power up the IC will stay in the suspend mode until I connect D+ and D- to a valid USB host?
Solved! Go to Solution.
09-01-2017 01:36 PM
You can't do that
We need to see the voltage present on VBUS transition to detect that the device is plugged in.
If you leave VBUS powered without being connected, the device will never enumerate because it will never detect a plug event.
09-04-2017 03:27 AM
Let me clarify my question once again. Please answer my questions one by one.
1. If I do not have a 5V VBUS and I have only a 3.3V VBUS - is it ok? Will the IC work normally?
2. If I connect a valid VBUS voltage and never connect D+,D- will the device remain in the suspend mode? Or such mode is incorrect at all and if I want the IC to stay in the suspend mode I should not connect VBUS at all?
3. What is the maximum time gap between a valid transition detection of VBUS and a connection of D+ and D-?
09-15-2017 10:04 AM
If it is interesting for anybody anywhere.
I've managed to produce a board with such connections:
1. Yes the IC works normally. No problem with the connection under Win7 and Putty at 115200.
2. Nope. If you connect VBUS and never connect D+ and D- the IC enters some undetermined state (only if OTP is programmed to the Modem only mode, I didn't observe such incorrect behaviour with the IC in the default mode) with the current consumption of about 5.5mA. If you then connect a valid D+ D- the IC enters the normal state and works as expected. But I've found as it seems to me a legitimate way to keep the IC in the suspend mode for as long time as I want to. I've added two 100k resistors to D+ and D- lines. Such connection keeps the D+ D- lines in the Idle state and the IC enters the suspend mode immediately after power up. It seems that these two resistors do not inrefere with the normal operation (but keep in mind that I have not conducted the complex testing, only 115200 via two Putty terminals).
3. Regarding all mentioned above I have not found the maximum time gap.
Remember that everything stated here is for information only. Use these information at your own risk.