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TPS57040 Buck vonverter, 13W

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cupoftea

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Hi,
I am doing a 38Vin, 30Vout, 13W output Buck with TPS57040 controller.
I have no ESD precautions available. And am working on a linoleum floor. The boards were assembled without ESD precautions.
None of the ten boards have worked....well, one did work, but gave only 26.5Vout when its divider was set for 30Vout (10k and 365k).
The boards use a compensation series RC of 133k and 10nF. Strangely, when i change the 133k to 10k, the board then doesnt work at all.

Do you agree that these problems all sound like ESD problems?

The layout isnt the best, but is what i am given...the inductor slightly overlaps the area of tracking of the compensation components.

The inductor that i have been given is 680uH and with Fsw of 313kHz, this gives a ramp of just 5%...but there's added internal slope comp.

TPS57040

Possibly the limitation to 26.5vout was due to the internal slope ramp, but the actual ramp given isnt stated in the datasheet, so theres no way of knowing?
Also, theres no way of knowing when the COMP pin has railed high, because the datasheet doesnt state the COMP pin range.
 
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Hi.

Pick one circuit.
Take some detail photos.
Show the schematic and the PCB layout.
Give a detailed error description.

I don't think that all immediately are killed by ESD. Linoleum is by far not as critical as vinyl.

Klaus
 
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Where did you buy the TPS57040 chips ?
Click to expand...
Thanks, ill check.
The device is MSL 3, one week floor life time after taking it out of the moisture protection bag. Need baking before reflow soldering after that time.
Click to expand...
Thanks, would you say this is unusual to have a component like this?

What is "floor life time", and d'you think it could be cause of problems seen?

...also, what about having to work without ESD precautions?.......do you agree this is bad news?...the TPS57040 is a tiny chip with a fet on it...i reckon they are getting zapped...do you?
 

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Apologies, I considered MSL common knowledge for electronic engineers. https://en.m.wikipedia.org/wiki/Moisture_sensitivity_level
If not stored/preprocessed appropriately, the devicec package can crack or delaminate during reflow solder, in my view one possible explanation for failure of a complete series. Other explanations have been already mentioned: counterfeit components, unsuitable solder methods.
 
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If not stored/preprocessed appropriately, the devicec package can crack or delaminate during reflow solder,
Click to expand...
Thanks very much for this....i wonder if i used too high temperature on the hot plate when i soldered them, and too high temperature of the hot air gun...i did have the air gun on 480degC?

...but doesnt this cracking or delaminating possibility apply to all chips when soldered?...or does the TPS57040 have particular susceptibility?

Do you think this could delaminate it?

A year ago i soldered ten LT3680 10MSOPs without problem...and just drag soldered them.....but did have esd mat/strap. Maybe LT3680 doesnt have this delamination problem...i will check datasheet.

LT3680 datasheet

..the LT3680 datasheet doesnt mention MSL , cracking or delamination anywhere, or any special details about solder over-sensitivity

It does sound to me, from what you are saying, that TPS57040 is a particularly sensitive chip?...compared to others?

With any IC, how do you know how sensitive it is to soldering heat?


Page 40 of the TPS57040 also says the following...
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates


..i am not aware of other ICs datasheets saying this, so i guess the TPS57040 is a sensitive chip(?)
 
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