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Posts: 6
Registered: ‎02-09-2017

CP2105 start-up time

Hello there!

 

I'm using CP2105 as my standard UART-USB bridge and I am generally very happy with the performance. But there is one little thing which bugs me and degrades the usability quite a bit. After connection a USB cable to the unit it always takes around 20 seconds until I can access the COM port from a PC. I don't have this problem with other interface ICs so I'm wondering why. I'm using the CP2105 in the self powered operation as recommended in the data sheet (see attached schematic) and the OS is Linux with kernel > 4.4.

 

I hope that someone can help me, thanks in advance!

Posts: 365
Registered: ‎09-04-2013

Re: CP2105 start-up time

Normally it takes more time when a new CP2105 device is connecting to host, the serial number is different for each device by default. Are you testing with different CP2105 devices? Viewing from the attached schematic, when the on-chip voltage regulator input (REGIN pin) is connecting to external 5V supply, then VDD is the voltage regulator output with typical 3.45 V. Not sure why the VDD/VIO is also connecting to VBUS. Figure 9 in CP2105 datasheet shows the typical self-powered connection. ESD protection diodes are required at the USB connector.
Posts: 6
Registered: ‎02-09-2017

Re: CP2105 start-up time

It takes a long time as well if I leave the device connected and reset the external power supply (can communicate with the CP2105 only after approx. 20 seconds after resetting the power). The VDD and VIO are not connected to VBUS, the PWR_FLAG has a different meaning in my EDA-software (necessary for ERC) and I omitted the ESD protection diodes because the CP2105 is part of a bigger system and the USB cable stays connected all the time.

Posts: 3,025
Registered: ‎02-07-2002

Re: CP2105 start-up time

Is linux maybe trying to detect if there is another device behind the serial port, like e.g. a modem?

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Posts: 6
Registered: ‎02-09-2017

Re: CP2105 start-up time

I have no idea but I don't think so because different interface ICs (Prolific, FTDI, ...) are working instantly. And if the device is recognized as a virtual com port there is no need for the OS to investigate further what's connected to it AFAIK.