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VREGIN on KL26

Question asked by Paddy Thomas on Jul 7, 2016
Latest reply on Jul 7, 2016 by xiangjun.rong


I have just made a PCB incorporating the MKL26Z128, and am having difficulty getting it working as a USB device. I completely overlooked the VREGIN pin which powers the USB transceiver, so left this unconnected originally. I managed to solder the pin to the 3.3V supply on my PCB, and this allowed a host to detect the device, however, no actual data could be transferred. Looking on the scope shows the D+ pin at 3V and the D- pin at 0V - is this normal behaviour in idle (unconnected) state? Does the VREGIN pin require 5V to operate correctly? The datasheet seems to hint that 2.7-5.5V is acceptable.

 

I included a regulator on the PCB to provide the 3.3V supply. I have a current requirement of about 200mA, and I believe the onboard regulator on the MKL26Z128 is limited to 120mA. Is there any benefit to utilising the onboard VREG for power, or is it fine just to use the external regulator?

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