Detailed Specification of the buck converter in STSPIN32F0/F0A?

[oneshot.triplekill]

Hi, guys

I am the newbee in using stspin32f0, so i had a question on buck converter which is integrated in it.

Since i use a 10uH inductor (typical value is 22uH in the AN5128), VDDA will shutdown when VM=18v~20v.

And, after replace it with two series 10uH(ie it is 20uH now), VDDA will disappear at VM=28v~30V now.

Further more, i have checked the SW signal with the oscilloscope.With 20uH inductor and VM=28~30v, the SW shows

a positive pulse width about 100~150ns. At this situation, even a little increase of VM will stop the SW and then the VDDA disappear.

So, can anyone help me to confirm the minimal Ton/pulse width of the buck inverter inside the stspin32f0?

The reason for this question is that, we are plan to make a BLDC using stspin32f0. When we test our first demo board, we find that the motor will stop spin when VM are greater than 15v. After our several days testing , we konw it is something realted to the stspin32f0's VDDA: when the VM is about 15v and a ripple with 5v vpp will cause VDDA drops form 3v3 to 0v.

the following pics shows what is happed befor motor stop:

CH2 is the VM , CH3 is VDDA, CH4 is SW.

pic1 is a whole overview.

pic2 is a zoom in which could tell the detailed things.

pic3 is the last SW pulse before the internal buck stop work.

So can we say that, the minium SW will be about 100~150ns?

And is there some mechanism that prevent the SW pulse short than 100~150ns?

Thanks!

[Tesla DeLorean]

@ST Community​ anyone covering motors?

[Enrico Poli]

Hi,

There is a dedicated AN about the buck converter of the STSPIN32F0 (AN5128) explaining the basic principles.

The SW behavior you posted fits with the normal operation of the converter, but I cannot say the same for the shutdown, of course.

I think something is triggering the overcurrent protection of the buck converter.

Following my suggestions:

• Keep the inductance value at 22 uH. Reducing the inductance means higher current spikes into the buck PMOS and more SW commutations.
• Try to reduce the output capacitor of the buck down to 10 uF.
• Check what is the root cause of the big noise on the VM.

Enrico

[oneshot.triplekill]

1.sure, we have already replace it to 22uH.

2.Okay, we will reduce the cap to 10uF

3.we have almost know the root cause of it: the wrong commutation of bldc driver mosfet.

So thanks for your confirm and reply~:grinning_face: