TLV62585: output over 3.3V (abnormal)

Hello Sway,

To be able to better understand the issue, could you please clarify the following questions:

1) I could not find the datasheet of the inductor used in your design. Could you share the datasheet/exact part number of the inductor used in your design?

2) What did you mean by the following statement? 

Sway Chen said:

The output has already changed to 2.2V cause my RfbT & RfbB followed the spec from (432k & 93.1K) change to 

(200k and 100k). 

Do you mean that you are still getting an output voltage of 2.2Volts? 

3) Can you also share the waveforms for Vin? 

4) How are you probing the switch node voltage?  Is the GND connection somewhere near the SW node pin? 

Thank you!

Best regards

Sneha 

1) I could not find the datasheet of the inductor used in your design. Could you share the datasheet/exact part number of the inductor used in your design?

ans: HC0320-L.pdf @ 1uH, https://www.atec-group.com/storage/system/product/atwspec/Inductive/Shielded_SMD_Power_Inductor/HC/HC0320-L.pdf 

2) What did you mean by the following statement? 

Sway Chen said:

The output has already changed to 2.2V cause my RfbT & RfbB followed the spec from (432k & 93.1K) change to 

(200k and 100k). 

Do you mean that you are still getting an output voltage of 2.2Volts? 

ans: I mean even I change the resistance pair, the ripple voltage is still poor, as the waveform I had posted.

3) Can you also share the waveforms for Vin? 

TBD

4) How are you probing the switch node voltage?  Is the GND connection somewhere near the SW node pin? 

ans: I use the ok wire to measure it.  It is the same point with Vin & Vout ground. ex: C5A or C1A. When I measure other versions the SW waveform is normal. You can refer to below:

Hello Sway,

Thanks for your reply. 

The schematic looks fine to me. I do not see any problem with the parameters used in the circuit.

Could you please share the waveforms for Vout and SW node again with lower time scale ( for ex: 2usec or similar), instead of 10msec ?   

Also, When you say you are getting normal SW waveforms with "other versions". What does "other versions" mean here? Please let me know.

Thank you!

Best regards

Sneha

Hello Sway,

Sorry I forgot to add this point in my earlier comment.

It would be great to have Max, Min, frequency values for both waveforms (Vout and SW).

Thanks!

Best regards

Sneha 

Hi Sneha,

I found the C5A may be wrong. It should be 4.7uF, but it placed 0.1uF when sample making. 

And then I need to some load avoiding the burst mode, so I can see the waveform smoothly.

However, do you have any recommendations about the output cap, is it possible to be lower? ex: L=1uh, output cap just 2.2uF (C5A) what are the pros and cons?

Anyway, thanks Sneha kindly support.

HI Sway,

Thanks a lot for the update. 

We do not recommend using lower capacitor values than datasheet specifications as it can affect the transient performance of the converter. The device is designed to have best performance with the datasheet recommendations only. Unfortunately, we cannot guarantee device behavior outside of datasheet specifications. 

The following app note explains the input and output capacitor selection procedure:

https://www.ti.com/lit/an/slta055/slta055.pdf?ts=1648024792643&ref_url=https%253A%252F%252Fwww.google.com%252F

Therefore, I would recommend to stick to the datasheet parameters. Please also refer to the LC matrix shown in the datasheet in page 10.

Let me know if you have any further questions. 

Thank you!

Best regards

Sneha 

Hi Sneha,

Do you know how to judge whether the IC is in PSM or PWM? What is the threshold? 0.1A or 3A as the spec figure14 and figure15

Is it possible to adjust by using an external circuit?

Thank you!

Hi Sneha,

Here are two more questions that need your help:

1. Is it 100p too large for C4A, do you have any calculated reference?

2. Is R3A not recommended to be used below 100k, or is R2A not over 400k?

CH1: SW node voltage

CH3: Vo (ac coupling)