TPS566231: Enable pin switching issue

Hi Sahil,

Just based on the waveform, is there a pull down resistor with high resistance at the MCU I/O? There's an internal 2uA pull up current source at EN.

If there's a pull down resistor, you can reduce the resistance and see if the waveform gets changed.

If not, the schematic of the converter is needed for further analysis.

Regards,

Andrew

Hi Andrew,

There is no pull down resistor on MCU I/O.

Please see the attached schematic snap.

MCU part#: STM32L562CEU6

Hi Sahil,

Thanks for the quick reply. Could you help to check the Vgs of Q13 first and share the waveform?

Regards,

Andrew

Hi Andrew,

For now, we have bypassed MOSFET and directly connected MCU_3V3_EN I/O of MCU to EN pin of switcher. 

We are getting the waveform as attached in my previous replies.

We have observed similar waveform with MOSFET also. 

Hi Sahil,

Let's locate the issue first. Based on the schematic and your description to connect the MCU_3V3_EN directly to EN pin of IC, if MCU_3V3_EN is pulled low to disable the IC, there will be 4.2V/11kohm=382uA current into MCU_3V3_EN. I'm not sure if the I/O pin of MCU has the current sink ability.

I recommend to first solder down the R482 resistor since there's a internal pull up circuit inside the IC. And check if the issue is addressed.

Regards,

Andrew

Hi Andrew,

We have already removed R482. 

So the scenario is the MCU I/O is directly connected to EN pin of switcher. There is nothing in the path.

Hi Sahil,

OK. So you directly connect the MCU I/O pin with the EN pin, then the MCU_3V3_EN signal itself cannot stay stable at 0V?

So please add a 10k pull down resistor between MCU_3V3_EN and GND.

Andrew

Hi Sahil,

I need to check with you about one thing. What's the EN signal you give for the provided waveform before?

Did you give a 3.3V stable output or a changing signal between 3.3V and 0V at MCU_3V3_EN?

Andrew

Hi Andrew,

We are giving pulse waveform on EN pin of switcher with 5sec delay.

Hi Sahil,

So the 3.3V MCU_3V3_EN voltage in waveform is correct, the issue is just the MCU_3V3_EN signal cannot stay stable at 0V after connecting with IC?

According to your test results and my experience on the test of TPS566231, we can make sure that there's no issue with the switcher itself at enable on/off.

So here are two of my recommendation now:

1. Add a 10k pull down resistor between MCU_3V3_EN and GND.

2. Try another I/O of MCU to see if the issue can be fixed.

Andrew

Hi Andrew,

We have tried both the options recommended by you but the issue remains the same.

Also, we have one other TI power switcher (Part#: TPS61236PRWLR) on our custom board whose EN pin is also being controlled by the same MCU with different I/O. That Logic is working fine for us.

So, the issue seems to be with TPS566231 EN pin. 

Please see below captured waveforms of Soft start pin and EN pin of TPS566231.

Image-1: When R473 is open and waveform are captured at EN & SS pin of TPS566231.

Image-2: When R473 is shorted and waveform are captured at EN & SS pin of TPS566231.

For both images: CH2 is SS pin and CH3 is EN pin.

Image-1:

Image-2: