TPS62743: open/short test

taichi

Expert 1395 points

Part Number: TPS62743
Other Parts Discussed in Thread: TPS62801, BQ2970

Hello

My Customer is verifying the safety of this IC.

How does the IC operate when the VO pin(C2 pin) of the TPS62743 is open?

Is there any possibility of smoke or fire the IC?

Regards

Taichi Nakamura

over 6 years ago

0 Chris Glaser over 6 years ago

TI__Guru*** 145640 points

Hi Nakamura-san,

I have never seen a request for open/short data on a WCSP (BGA) device. I think this failure mode is extremely unlikely. Especially being an interior pin, if the VOS pin were to open, other pins would open as well and the whole IC would have to be tilted.

If this connection were broken somehow, there should be no smoke/fire.

We also have the smaller TPS62801 as a higher current option.

0 Dave Pulvermacher over 6 years ago in reply to Chris Glaser

Intellectual 870 points

I am wondering about the built-in short circuit protection. When I short the inputs to my board, there is no smoke, but the power supply does not recover either. I have to remove power (battery) and reapply. This will not be possible on the end product. Section 8.3.6 on the datasheet has a short blurb on short protection but, for me, it did not work. What else can I do if my board short circuits temporarily? I need it to recover and be operation.

My battery has a standard PCM built in as well.

0 Chris Glaser over 6 years ago in reply to Dave Pulvermacher

TI__Guru*** 145640 points

Hi Dave,

Is this a new/different topic from the open/short behavior? It sounds like you are rather asking about placing a short at the output of the TPS62743?

Yes, the device should auto-recover from an output short. Can you send a waveform (Vin, Vout, SW, EN) of applying the short and then removing it?

0 Dave Pulvermacher over 6 years ago in reply to Chris Glaser

Intellectual 870 points

In fact, Chris, it's a short at the input, from Vin to Ground. Are you saying the short circuit protection in the TPS62743 is for the output? 2018-04-25_15-09-42.pdf 2018-04-25_15-09-42.pdf

0 Chris Glaser over 6 years ago in reply to Dave Pulvermacher

TI__Guru*** 145640 points

Thanks for clarifying. Yes, most all power supplies I have seen just protect the output from a short there. This is what they provide. The IC has no control over what the system gives it on its input.

Your schematics looks fine. Could you send the waveform of what you do?

As well, we have the new TPS62801/2 which are much smaller but a little higher Iq.

0 Dave Pulvermacher over 6 years ago in reply to Chris Glaser

Intellectual 870 points

Ok, thanks. I don't have a waveform at the moment and it will be next week before I can generate one. I don't need smaller at this point, but low low power. Can you recommend a device to help with short circuits at the input?

0 Chris Glaser over 6 years ago in reply to Dave Pulvermacher

TI__Guru*** 145640 points

It's not clear what your concern is. Is it possible for the input to be shorted by the user in your end application? If the battery is not removable, how would it become shorted (and then un-shorted)?

As well, if you are using a re-chargeable battery, the charger usually takes care of this through numerous battery protection features.

0 Dave Pulvermacher over 6 years ago in reply to Chris Glaser

Intellectual 870 points

There are exposed contacts for recharging. Yes, I agree, rechargeable LiPo should have protection! But this one is coming up short, no pun intended.

Thanks again for your help.

0 Gautham over 6 years ago in reply to Dave Pulvermacher

TI__Genius 12475 points

You might look at something like
www.ti.com/.../bq24311
www.ti.com/.../BQ2970

0 Dave Pulvermacher over 6 years ago in reply to Chris Glaser

Intellectual 870 points

Chris -

Here is scope shot of 3.0v volts when I short the battery leads on my board. I cannot detect damage, just that the board does not recover.

The 1.5v pulse you see above begins after about 2 seconds of just a flat 0v signal.

I am ordering a BQ2970 eval kit to try this solution. But I am skeptical of it helping.

0 Chris Glaser over 6 years ago in reply to Dave Pulvermacher

TI__Guru*** 145640 points

Thanks for sharing Dave. Can you add Vin and SW to the waveform and zoom in on 1 of those pulses?

0 Dave Pulvermacher over 6 years ago in reply to Chris Glaser

Intellectual 870 points

Sure thing, Chris. 3 images attached. First details 'normal' behavior. There are some 3.4kHz spikes I wasn't aware of!

normal

after a short

zoomed in after a short

0 Chris Glaser over 6 years ago in reply to Dave Pulvermacher

TI__Guru*** 145640 points

Thanks for sending.

What level is Vin at (it's hard to tell since it is so low on the scope)? Can you move that trace up a little on the scope, so it is not hidden? What voltage does it measure with a multimeter?

0 Dave Pulvermacher over 6 years ago in reply to Chris Glaser

Intellectual 870 points

It's powered by a LiPo battery. Right now it's running at about 3.8v.

0 Chris Glaser over 6 years ago in reply to Dave Pulvermacher

TI__Guru*** 145640 points

Yes, I remember that is your application. But in the 3 waveforms you showed, I don't think Vin is at 3.8V. Can you move the yellow trace higher on the scope so it can be seen? What DC voltage is this at (after the short)?

0 Dave Pulvermacher over 6 years ago in reply to Chris Glaser

Intellectual 870 points

Chris - shoot, should have looked closer. Battery V is hovering between 1.9 and 2.2v after a short. So no wonder SW is not turning on.

I removed the battery from the circuit and shorted it again and it recovered right away, as expected. Something is holding it down. I'll investigate further but suggestions would be most welcome. Thank you.

After a short:

0 Chris Glaser over 6 years ago in reply to Dave Pulvermacher

TI__Guru*** 145640 points

Thanks for confirming Dave. Yes, something is holding down the battery voltage. There may be a protection circuit inside the battery pack itself that limits the battery source current to a very small amount when its voltage is so low. I suppose you could measure this by shorting the battery (with a resistor decade box, for example) and then slowly increasing the resistance of the short to make a V-I curve of the battery voltage recovery after a short.

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TPS62743: open/short test