TPS57112-Q1: Question about current limit

Yuta Kurimoto

Part Number: TPS57112-Q1

Hello Team,

Thanks for your support. I have 2 questions about current limit feature.

Q. I think this device is cycle by cycle current limit. I would like to know the timing when the current limiting behavior is happened. Is it immediately worked when the high- side switch current hits the threshold? OR is there any delay between overcurrent detected and current limiting happened?

Q. In the datasheet, the current limit threshold is 2.9A(min), 5.3A(typ). What is the maximum value?

Thanks,

Yuta Kurimoto

over 6 years ago

0 JohnTucker over 6 years ago

TI__Guru**** 191445 points

Kurimoto-san,

Yes the current limit is cycle by cycle, so the current limit happens within the same switching cycle. There is a blanking time at the beginning of the on time when the current limit is masked equal to the minimum on time.

I do not have data for the maximum current limit value. I have researched this previously, and I believe it is rather large, possibly greater than 8 A.

0 Yuta Kurimoto over 6 years ago in reply to JohnTucker

TI__Genius 10655 points

Hello John,

Thanks for your quick answer!
Q. Do you have any char data of minimum ON time so that we can know the MIN/MAX value of minimum On time?

Yuta Kurimoto

0 JohnTucker over 6 years ago in reply to Yuta Kurimoto

TI__Guru**** 191445 points

Kurimoto-san,

I am reasonably sure that minimum on time is part of characterization. I am out of the office until Tuesday. Can I get you the data then? There is a relevant app note as well:
www.ti.com/.../slva877.pdf
It will apply to TPS57112-Q1 as well.

0 Yuta Kurimoto over 6 years ago in reply to JohnTucker

TI__Genius 10655 points

Hello John,

I need to answer this question on Tuesday Japan time.
If you can provide the answer until then, it is good.

Thanks,
Yuta Kurimoto

0 JohnTucker over 6 years ago in reply to Yuta Kurimoto

TI__Guru**** 191445 points

Kurimoto-san,

I will be back in the office tomorrow. I can research the test results then.

Regards,

0 JohnTucker over 6 years ago in reply to JohnTucker

TI__Guru**** 191445 points

Kurimoto-san,

For the minimum on time, the data suggests 3 sigma limits over temperature as 68.4 nsec to 99.8 nsec, at 5 V in and 500 kHz operating frequency. That corresponds to less than 2.5 V output voltage, so I think the test condition is not representative of actual in circuit performance. That said, there is an app note about high frequency, low on time operation:

www.ti.com/.../slva877.pdf

That app note has simulation results indicating a maximum min on time of 94.9 nsec at 2.5 MHz and 1.35 V output voltage.

Let me know if you have further questions.

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TPS57112-Q1: Question about current limit