Hello,

I am using a USB to TTL converter for the communication of our product to PC. When the product is in OFF condition and USB cable is connected to PC, I am getting ~ 1.8 V in the Vcc pin of the Microcontroller. Which cause damage of our product in this situations. Then i am verify the signal level of Rx & Tx found Rx is High and Tx is in Low level. How to avoid this voltage please suggest ??
Operating voltage of Product is 3.3 V

 

Does your product have its own power supply that shuts down when not in use, or can you add an on/off switch in series with the 1.8V.

There is a more component-intensive solution which is to detect the USB data transistions and enable your device when they are available.

 

Does your product have its own power supply that shuts down when not in use, or can you add an on/off switch in series with the 1.8V.

There is a more component-intensive solution which is to detect the USB data transistions and enable your device when they are available.

Yes, Product having own supply & When not used it is product will be OFF. But USB to TTL cable always connected to PC.

 

Would it suit your needs to use a small relay or solid state swtich which kept the voltage from USB open unless the power supply was turned on?

I realize this could lead to complicated system of interlocks, but for now, let's keep it simple.

 

Is the product normally powered off the USB form the PC ?

USB to TTL convertors depending on the type, cna be powered off the USB or off the board its plugged into

I'm guessing your saying this convertor is powered off the PC , using the USB 5v,

Is this 1v8 your reading coming from the 5V power on the USB directly, or is it the TTL lines out of the USB to ttl chip driving the board ?

When you say permanently connected, is this built onto the board, or an external off the shelf USB to TTL "soap on a rope"

can you share a picture and schematic of the bit please,

Its unusual to see 1v8 on the Vcc of a board, coming from the USB, as that implies its supplying a good few mA,
its usual to see a few volts on inputs, as the TTL out of the convertor is still driving your baord.

The one I fell into recently , was a pull up on a convertor chip,
it went from a pin of the USB to TTL chip, to my board,
and it seems that the USB to TTL chip put volts out on this pin even when we told the chips interface to our board to "reset"

Phantom driving is sometimes hard to find.

The classic in the day, was you could put a DRAM on a board, and not connect its power pins,
it had sufficient leakage from the inputs begin drive to keep working
till you had the all zero case on the inputs for "to long".