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Micro-controller not detected by PC when connected by USB

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abdulsamad.zahir

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Hi Everybody,

I'm working with an MK20DX256VLH7 (Cortex M-4) paired with an MKL02 on one board. This board is connected to another board which contains the microUSB port. The two boards connect to each other using headers to upload the code to MK20. However, when I try to upload the code using USB connection, board's not detected by the PC (nothing shows up on device manager - device is not even detected as "unknown device"). The workaround has been to detach the boards, cut a USB cable, solder the USB wires to the pins (V_USB, D_N, D_P, GND) and upload the code. This way, the device is recognized and the code is uploaded. Afterwards, I can de-solder the wires, and upload my code using microUSB port which was previously not detected by PC.

This is quite strange since we've used these chips before and we've never faced any issues before.

I'd greatly appreciate it if someone could help in finding what's causing this problem.

If any further details are needed, let me know please.

View attachment Design (1).PDF
 

Hi,

Too much current drawn from the USB?
Measure USB voltage at the target and current.

Klaus
 

Hi,

I haven't tested the current draw from USB port, but the unit wasn't drawing much current when initially connected to power supply. Even after enabling basic functionalities like LEDs, the current draw was as high as 0.02 A for a while. If I remember the figures right, V_USB, D_N and D_P pins had voltages as high as 4.8 V. How could this affect USB though? Could you elaborate please?

However, that's a good point you raised. Initially, the board was drawing 0.01 to 0.02 A. However, after a while even though only MCU is operational, the current draw was going as high as 0.06 A. This happened after I started experimenting with some pin connections and was driving them externally. Could that be due to a damaged pin on MK20 leaking current? Or is it another problem?
 

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