TPS92380: Question about SW terminal behavior just after powered on.

Kazuya Nakai59

Part Number: TPS92380
Other Parts Discussed in Thread: TPS92360

Tool/software:

Hello guys,

One of my customers is evaluating TPS92380 using the SEPIC circuit shown on page 28, Figure 9-4 of the datasheet.
At this moment, they have the following questions.
Could you please give me your reply?

Q1.
Due to the microcontroller's initial setting, VDDIO/EN, SYNC connected to VDDIO/EN, and PWM terminals are high level
for approximately 5 ms just after powered on. After that, VDDIO/EN, SYNC, and PWM terminals went to low.

Approximately 60 ms later additionally, the SW terminal cycles on and off multiple times and goes low level after that.
At this timing, the voltage at VOUT (the cathode side of the rectifier diode) is boosted.

Is this SW terminal on/off cycling normal behavior for the TPS92380?
In other words, once soft start begins, will SW cycle on and off multiple times at the end of soft start even if VDDIO/EN terminal is set low during soft start?

Q2.
When the timing that SW is turned on and off multiple times, does SW OVP and output OVP protection work correctly though VDDIO/EN = L?
If the the answer is No, is there a possibility that damaging the TPS92380 by the SW terminal voltage and output voltage rising?

Q3.
Can the information and formulas in 8.3.1.2.1 "Using Two-Divider" and 8.3.1.2.2 "Using T-Divider" be applied to SEPIC mode?

Q4.
Is the content of 9.2.3.1 "Inductor Selection" applicable in SEPIC mode?
It also states that "A saturation current rating of at least 4.1 A is recommended for most applications.."
However, the TPS92380's maximum current IMAX is 120mA, which is far more than 4.1A.
What is concern when the inductor saturation current is less than 4.1A and why is it set at 4.1A?

Your reply would be much appreciated.

Best regards,
Kazuya.

1 month ago

0 Colin Chen 1 month ago

TI__Mastermind 21361 points

Hi Kazuya,

Please give me some time to check. Thanks.

Colin

0 Kazuya Nakai59 1 month ago in reply to Colin Chen

Guru 21645 points

Hi Colin,

Thank you very much for your reply.

I see. I will wait for your next reply.

Thank you again and best regards,
Kazuya.

0 Colin Chen 29 days ago in reply to Kazuya Nakai59

TI__Mastermind 21361 points

Hi Kazuya,

Thanks for your understanding. I am busy these days.

I will reply you next Monday. Sorry about it.

Thanks,

Collin

0 Kazuya Nakai59 25 days ago in reply to Colin Chen

Guru 21645 points

Hi Colin,

Thank you very much for your support.

Could you give me your update if you have any information?

Thank you again and best regards,
Kazuya.

0 Colin Chen 25 days ago in reply to Kazuya Nakai59

TI__Mastermind 21361 points

Hi Kazuya,

Sorry for late, below is my answer;

Q1:SW would stop cycle as long as VDDIO/EN is low. The phenomenon why you see SW keep cycling after MCU set VDDIO/EN to low is there is a cap in VDDIO.EN to GND. It need some time to discharge to 0.

Q2: same with Q1

Q3: Yes, it can be used.

Q4：120mA is signal channel of device not the total current. The inductor peak current can be larger than output current due to VIN and Vo.The cause of Inductor saturation current set to 4.1A is we must keep the inductor current limit lower than I_SAT. Which can prevent inductance drop too much in short circuit condition.

Can we know the project information and EE for this device? You can reach out to me for further discussion.

colin-chen@ti.com

Colin

0 Kazuya Nakai59 23 days ago in reply to Colin Chen

Guru 21645 points

Hi Colin,

Thank you very much for your reply.

I'm sorry that I told you a wrong explanation in the previous Q1.

Wrong: Approximately 60 ms later additionally, the SW terminal cycles on and off multiple times and goes low level after that.

Correct: Approximately 60 ms later additionally, the SW terminal cycles on and off multiple times(2~3 times) and becomes off state.

They checked VDDIO/EN pin of tps92360 with an oscilloscope. 5ms after power-on, VDDIO/EN is at L level. The VDDIO/EN level remains at L. However, total 65ms after power-on, the SW terminal turns on and off multiple times before turning off. At this time, VDDIO/EN is at L level.

Q. If VDDIO/EN = L, will the SW terminal not turn on under any circumstances?

Thank you again and best regards,
Kazuya.

0 Colin Chen 23 days ago in reply to Kazuya Nakai59

TI__Mastermind 21361 points

Hi,

Give me some time to check it.

Colin

0 Colin Chen 23 days ago in reply to Kazuya Nakai59

TI__Mastermind 21361 points

Hi Kazuya,

The SW wouldn't switching with EN=L.

Could you show me the schematic? And waveforms you said?

It is not direct to know the issue by the description.

Thanks,

Colin

0 Kazuya Nakai59 23 days ago in reply to Colin Chen

Guru 21645 points

Hi Colin,

Thank you very much for your reply.

Could you tell me your e-mail address because they don't want to disclose their schematic and waveform?
I will send these to you when I get your e-mail address.

Thank you again and best regards,
Kazuya.

0 Colin Chen 23 days ago in reply to Kazuya Nakai59

TI__Mastermind 21361 points

Hi Kazuya,

My email address: colin-chen@ti.com.

Let's transfer to email support.

Thanks,

Colin

0 Kazuya Nakai59 6 days ago in reply to Colin Chen

Guru 21645 points

Hi Colin,

Thank you very much for telling your e-mail address.

I'm very sorry my response to be very late.

I sent you a document but the message was not delivered due to my mistake (E-mail address input was wrong).

I sent you a explanation again.
Could you please take a look and please give me your reply?

Thank you again and best regards,
Kazuya.

0 Colin Chen 6 days ago in reply to Kazuya Nakai59

TI__Mastermind 21361 points

Hi Kazuya,

Sure, let me check your email.

Closed this thread temporily.

Thanks,

COlin

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TPS92380: Question about SW terminal behavior just after powered on.