I have some modules, each with their own STM32 MCU, connected on the same power supply. These modules are communicating via UART.
When plugging in multiple units I get the problem that modules are seemingly randomly breaking down. They do still work (the LCD lights up). But the STM32 chip gets very hot and draws a lot of power.

At first, I thought it would maybe be overshoot at the power supply rail from hotplugging that caused these failures. But when further investigating (I now only have broken modules left), I found out that there was a substantial current of 0.1A running over the UART lines.

I have the theory that when one board is not powered, it draws current via the UART port protection diodes, and this is what breaks the board supplying this power since it needs to deliver the full power of a board via its RX pin. I made a schematic explaining this:

Is this something that could break my STM32? It is something that happens very quickly because the board does not seem to power up from this current.

What would be the best way to fix this issue?

I have some modules, each with their own STM32 MCU, connected on the same power supply. These modules are communicating via UART.
When plugging in multiple units I get the problem that modules are seemingly randomly breaking down. They still work (the LCD lights up) but the STM32 chip gets very hot and draws a lot of power.

At first I thought it would maybe be overshoot at the power supply rail from hotplugging that caused these failures, but when further investigating (I now only have broken modules left,) I found that there was a substantial current of 0.1A running over the UART lines.

I have the theory that when one board is not powered it draws current via the UART port protection diodes, and this is what breaks the board supplying this power since it needs to deliver the full power of a board via its RX pin. I made a schematic explaining this:

Is this something that could break my STM32? It is something that happens very quickly because the board does not seem to power up from this current.

What would be the best way to fix this issue?

I have some modules, each with their own STM32 MCU, connected on the same powersupply. These modules are communicating via UART. When plugging in multiple units I get the problem that modules are seemingly randomly breaking down. They do still work (the lcd lights up). But the STM32 chip gets very hot and draws a lot of power.

At first, I thought it would maybe be overshoot at the powersupply rail from hotplugging that caused these failures. But when further investigating (I now only have broken modules left), I found out that there was a substantial current 0.1A running over the UART lines.

I have the theory that when one board is not powered, it draws current via the UART port protection diodes, and this is what breaks the board supplying this power since it needs to deliver the full power of a board via its RX pin. I made a schematic explaining this:

Is this something that could break my stm32? It is something that happens very quickly because the board does not seem to power up from this current.

What would be the best way to fix this issue?

I have some modules, each with their own STM32 MCU, connected on the same power supply. These modules are communicating via UART.
When plugging in multiple units I get the problem that modules are seemingly randomly breaking down. They do still work (the LCD lights up). But the STM32 chip gets very hot and draws a lot of power.

At first, I thought it would maybe be overshoot at the power supply rail from hotplugging that caused these failures. But when further investigating (I now only have broken modules left), I found out that there was a substantial current of 0.1A running over the UART lines.

I have the theory that when one board is not powered, it draws current via the UART port protection diodes, and this is what breaks the board supplying this power since it needs to deliver the full power of a board via its RX pin. I made a schematic explaining this:

Is this something that could break my STM32? It is something that happens very quickly because the board does not seem to power up from this current.

What would be the best way to fix this issue?