TPS54620 Over Current Protection foldback?

Refael Shamir

Other Parts Discussed in Thread: TPS54620, TPS62180, TPS54622

Hi,

I use in my design a DC-DC converter TPS54620, and am interested in testing its current limiting operation in short circuit mode.

My test setup is as follow:
- Creating a short circuit between Vout and GND.
- Placing a DVM (in current mode) between TPS54620 output pin, and short circuit.
- Measuring output voltage during operation via scope.
- Temperature measurement with a thermo-couple measurement device.

Test results are as follow:
- Output current is at 9.4A (steady).
- Output voltage is ~150mV.
- Temperature reached := 94 degree Celsius (after prolong operation).

My questions are:
- Can the output current limit be lowered?
- Why there is no fold-back operation (as shown in the attached - right graph), whereas my unit behaves like the left graph)?

Can you help me with the above?

Thanks,
Refael.

over 8 years ago

0 JohnTucker over 8 years ago

TI__Guru**** 191445 points

The current limit is fixed internally. It is designed to operate without current foldback.

0 Chris Glaser over 8 years ago

TI__Guru*** 147230 points

The TPS62180 has hiccup protection which is a type of foldback.

0 Refael Shamir over 8 years ago in reply to JohnTucker

Prodigy 250 points

Hi John,

Thank you for your reply.

Can you please explain than the following paragraph from TPS54620 datasheet:

"The device implements current mode control which uses the COMP pin voltage to control the turn off of the highside MOSFET and the turn on of the low-side MOSFET on a cycle by cycle basis. Each cycle the switch current
and the current reference generated by the COMP pin voltage are compared, when the peak switch current
intersects the current reference the high-side switch is turned off."

Thanks,
Refael.

0 JohnTucker over 8 years ago in reply to JohnTucker

TI__Guru**** 191445 points

TPS54622 is pin compatible and has hiccup OCP also.

0 JohnTucker over 8 years ago in reply to JohnTucker

TI__Guru**** 191445 points

What is it you do not understand? It just says the peak switch current is proportional to the COMP pin voltage. That is pretty much standard for peak current mode control topology.

0 Refael Shamir over 8 years ago in reply to Chris Glaser

Prodigy 250 points

Hi Chris,

As I understand, hiccup protection refers to momentarily short circuit interrupt.
My question is in regard a situation where there is a constant short circuit present at start up, it seems that TPS54620 will continue on drawing current and thus reaches a very high temperature.

I'm looking to limit drawn output current.

0 JohnTucker over 8 years ago in reply to Refael Shamir

TI__Guru**** 191445 points

hiccup mode means that after a certain time duration of OCP operation, the device shuts down then after a delay time attempts to restart. If the fault is still present the OCP will reactivate and after the delay time the device will again shut down. This will repeat until the fault is removed, hence the term "hiccup" mode.

0 Chris Glaser over 8 years ago in reply to Refael Shamir

TI__Guru*** 147230 points

You understand incorrectly. See figures 32 and following in the D/S. This is the whole point of hiccup--reduce the input power drawn and temp rise during a severe fault.

As John mentioned, TPS54620 does not have hiccup so it behaves as you have seen.

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TPS54620 Over Current Protection foldback?