KV5XP indirect power supply through a IO-Pin

[stephanschade]

Hi

We have a Problem with a KV5XP Controller: 

A USB to UART Bridge is connect at the Controller, the Bridge is supplied over the USB-Power.

The problem occur when the USB is connect and the Power of the controller is down. The TXD of the Bridge give a high level signal (3,3V) to a controller-pin. This voltage level make a indirect power supply on the 3,3V rail of the controller.

How i can solve this problem?

[john_suchyta]

Hi Stephan. The KV5X has GPIO pins that can cause this issue. The datasheet mentions that the pin voltage should be no higher than VDD +0.3V. This is the requirement for powered and unpowered operation. While you can get away with biasing GPIO on some other unpowered Kinetis MCUs, the KV5X and other high speed Kinetis devices exhibit the behavior you see - the VDD node will be biased internally through the biased PFET driver. This change was required for the high speed parts.

The only solution is to insert a switch between your Bridge I/O and the KV5X GPIO, and control it with an active signal from the KV5X.

Regards,

John