Electronics > Projects, Designs, and Technical Stuff
The TLV760xx regulators are a nice piece [s]of crap[/s]
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Siwastaja:

--- Quote from: bloguetronica on February 10, 2019, 06:42:35 pm ---Well, I'm just plugging and unplugging to an already on power supply. That should pose no issue.

--- End quote ---

This poses a HUGE issue and will often kill any IC unless you design a correctly damped input circuitry. This is basically an RC snubber.

Basics.

Tim explained it very well above.
T3sl4co1l:
My explanation seems not to have been read... :-\

The other thing that absorbs surge (and prevents reverse polarity) is a TVS diode.  You want the TVS's peak voltage rated within the regulator's maximum, which is higher than the TVS's nominal rating by a modest amount.  So a 30V regulator might need a 24V TVS.

Again, this does nothing for overcurrent, which one should not rely on with such a tiny LDO, or really, in general.

Tim
bloguetronica:
Ok, did some experiments by putting a 220 \$\Omega\$ resistor at the input. Did some short circuits upstream to the regulator, to create some spikes, and the TLV76050 held pretty well. Raised the voltage to 28V and used another resistor in parallel with the first one, this time it was a 82 \$\Omega\$ resistor. Again, it held. So I can assume that the spike issue is solved. A 100 \$\Omega\$ resistor works with some margin.

Another issue, and that might have fried the AD5551, are the peaks during unplugging. By using 100nF capacitors at the input and the output, as described in the datasheet, I can observe peaks a bit larger than 6V, on some rare occasions after disconnecting. I can reduce those peaks by using 1uF capacitors. See the image attached. After the sample, I couldn't get peaks greater than 5.72V.


--- Quote from: T3sl4co1l on February 10, 2019, 07:50:22 pm ---My explanation seems not to have been read... :-\

The other thing that absorbs surge (and prevents reverse polarity) is a TVS diode.  You want the TVS's peak voltage rated within the regulator's maximum, which is higher than the TVS's nominal rating by a modest amount.  So a 30V regulator might need a 24V TVS.

Again, this does nothing for overcurrent, which one should not rely on with such a tiny LDO, or really, in general.

Tim

--- End quote ---
Your explanations were read. The 24V in the final application will be provided by an isolated DC-DC converter, which will be soldered onto the board. However, I'll still use a 100 \$\Omega\$ resistor in series with the input of the regulator just to be on the safe side. A TVS will serve no purpose there, because if the DC-DC converter outputs a peak, it will fry the diode plus the regulator.

Kind regards, Samuel Lourenço
T3sl4co1l:

--- Quote from: bloguetronica on February 10, 2019, 08:08:00 pm ---A TVS will serve no purpose there, because if the DC-DC converter outputs a peak, it will fry the diode plus the regulator.

--- End quote ---

How sure are you of this?  -- What's the converter's capability?  What size diode did you have in mind?

I have an application that uses a switching converter to dump six hundred watts into a trio of SMC sized TVS diodes.  They take this abuse for almost a full second before simply getting too hot (I have thermal protection in the circuit).  TVS diodes are damn good at their job. :)

Tim
bloguetronica:

--- Quote from: T3sl4co1l on February 10, 2019, 08:12:00 pm ---
--- Quote from: bloguetronica on February 10, 2019, 08:08:00 pm ---A TVS will serve no purpose there, because if the DC-DC converter outputs a peak, it will fry the diode plus the regulator.

--- End quote ---

How sure are you of this?  -- What's the converter's capability?  What size diode did you have in mind?

I have an application that uses a switching converter to dump six hundred watts into a trio of SMC sized TVS diodes.  They take this abuse for almost a full second before simply getting too hot (I have thermal protection in the circuit).  TVS diodes are damn good at their job. :)

Tim

--- End quote ---
I think that this application doesn't need to have that. The DC-DC converter itself is well regulated. If something goes wrong, then the whole board is toasted. Anyway, I'm planning to use the resistor and perhaps a 1206L005 in series with the input of the regulator. It is a bit of over-engineering, but if the board comes with the 5V rail shorted right after soldering, I won't get damaged components. A TVS will be used, for sure, but only at the input of the board, along with a nice big PPTC fuse and a SCR crowbar.

Kind regards, Samuel Lourenço
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