STM32H735 custom board power draw

[Neutron235]

Hi,

Ive made a custom board with a STM32H735 micro on it. I have built a board with nothing but a micro and a few of its needed passive components and went to provide it power and test that its working. I supplied power from a benchtop power supply with a current limit of 400ma and it hit this limit at 3v. Dropping to 100ma it hit the limit at 2.2V. Checking the resistance on the power rails it 10.25k and the Vcap rail is 500k. Thermal camera shows a square heat zone expanding from the centre of the IC (LFQP package) towards the outside. Ive now tired 3 different ICs on 3 different boards. The schematic is very similar to the STM32H735G-DK  with changes mostly being things like jumpers. What could be causing this issue and what steps can i take from here?
Thanks in advanced

[Neutron235]

Yeah 1.62v is min operating technically.

Using STM32CubeProgrammer im getting :

18:29:43 : Error: Unable to get core ID
18:29:43 : Error: No STM32 target found! If your product embeds Debug Authentication, please perform a discovery using Debug Authentication

[LCE]

> There is a zero ohm connected to VFBSMPS, its currently not populated.
> The datasheet and application note say that the internal SMPS can either
> power the core directly or via the internal LDO. this zero ohm would
> allow me to make that connection externally.

Not so sure about this, the SMPS needs some feedback signal, and that's VFBSMPS.

So try with the 0R.

That might explain why you measure something close to input voltage, your "VDD" should be something around 1.1V (check datasheet).

This pic from AN5419 about H7 power (red notes by me):

[Neutron235]

So my first board tried number 1 and was shorting on the VDDSMPS pins.

The zero ohm there lets me put it into type 2, i have another that lets me go into type 3.

No matter this config the VFBSMPS is connected correctly

[LCE]

> No matter this config the VFBSMPS is connected correctly

What do you actually mean?

Is VFBSMPS connected or not?

Again, for SMPS I'm pretty sure it must be connected.

pin description:

[Neutron235]

Yes, VFBSMPS is connected as is VDDSMPS

[AScha.3]

Hi,

show your actual circuit, as it is connected (with 0r or not ).