I noticed a strange problem while attempting to program a STM32F051 device. The device is part of a larger circuit and gets its supply voltage from a 3.3V LDO regulator and the VDDA is supplied by a 3.3 V REF source. The problem is that I am not able to program the device using KEIL - it messages "no target connected" and using the STM-Link utility it is also not possible to log into the device (even if the reset pin is used for interconnecting under reset). The only way to program the device is by switching the boot0 to high.
What I've tested so far was to bridge the both ferrites inside the supply lines for VDD and VDDA - this at least sporadically allowed for programming the device.
Since earlier layouts using the same circuit never showed such behaviour I would be very happy if someone might give a hint what part of the circuit is close or beyond to the edge of what would work.
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