TPA6211A1: Thermal Pad Electrical no Internal Electrical Connections?

Hi, Are you planning to connect the Pad to a different potential than GND? Or leave it floating?

Please notice that data sheet specifies to connect this to GND at the Pin Function table. And also recommends to not leave it floating as it could affect thermal and mechanical performance.

The impedance from GND pins to pad is widely variable, it is recommended to connect pad to GND plane same as GND pins.

Best regards,
-Ivan Salazar
Applications Engineer

Hi Ivan,

Yes I'm planning to do a low side current measurement like this: https://e2e.ti.com/support/audio-group/audio/f/audio-forum/1031942/tpa6211a1-low-side-current-monitor-for-audio-amplifier?tisearch=e2e-sitesearch&keymatch=TPA6211A1#

So in the current configuration the GND pin will be have some offset, whereas the thermal will be connected to ground. Will, this arrangement work as expected? Or should the thermal pad be connected to the same potential as the GND pin?

If the pad is purely for thermal and mechanical reasons, there should be no affect on this measurement right?

Cheers,

Hi, I recall there is some information about the connection from Pad to GND pins, let me look for it and will share by early next week.

Best regards,
-Ivan Salazar
Applications Engineer

Hi, here's the information I found about this Pad connection to GND:

"I have found that this impedance is generally high, but this is not certain.  It varies widely over process and temperature.  It can be less than 1ohm, and it is not a variable we can control or guarantee.  So I think it is risky to try to detect current from the ground pin with less than 1ohm in parallel."

In addition, at that time it was suggested to consider current detection at VDD instead.

Best regards,
-Ivan Salazar
Applications Engineer

Hi Ivan,

Ok, that's good to know, are there are similar parts you can recommend that, do control this? Footprint compatible would be ideal but, any suggestions would be really useful.

I've noticed in some other posts that some IC"s don't have the power-pad and ground connected or at least they control the impedance between the two? 

e.g  https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/933868/drv8837-low-side-current-measurement-in-drv8837?tisearch=e2e-sitesearch&keymatch=DRV8837#.

Hopefully there are some IC's like this for audio amplifiers?

Thanks,

Hi, I'll need to double check on this, let me plan for this and let you know if there are any options. Is the pad required at all? Or you just need to add the current detection on GND pins?

Best regards,
-Ivan Salazar
Applications Engineer

Hi Ivan,

Awesome, the current detection on the GND pins is the main thing.

Thanks,

Hi, understood, I won't narrow the search for devices with pad then, thanks for clarification. Will keep you updated.

Best regards,
-Ivan Salazar
Applications Engineer

Hi, would BGA be an option for this application? Perhaps you can consider TPA6205A1 in BGA package which does not have a pad.

Best regards,
-Ivan Salazar
Applications Engineer

Hey Ivan,

Trying to stay away of from BGA's at this point, it would be the only one on the board.

Would prefer an SMT component, are there any other options in different footprints that would work? Open to other options you can suggest

Thanks,

E-Q

Hi Ivan,

What if I connected the PAD to the chip ground pin and then had a low side resistor to system ground, would that be fine? I could add a thermal plane on all layers the same size as the pad underneath the thermal pad, would this be sufficient for proper thermal performance of this IC? 

Or are there any other parts where the PAD and ground pin are not internally connected?

Cheers,

Hi, That may be a good idea although not sure how to ponder the impact on thermal performance. I would think it is OK as long as the device is not pushing full output power for extended time.

Best regards,
-Ivan Salazar
Applications Engineer

Hi Ivan,

Ok cool, I might look into this option then, approximately what would you consider extended time for this device if running at a power level of 1 watt into a 8ohm load?

Also, what would your team suggest is the smallest thermal pad  size, if using the above configuration (thermal pad on all layers under the power-pad)

Cheers,

Kevin M

Hi Kevin,

I assume you're using VDD = 5V correct? 1W into 8Ohm may be OK for continuous playback. Lower load would demand higher current, but you're using the higher load impedance.

You may want to extend over the top and/or bottom side of the IC wherever you have some space, couldn't comment on specific size for minimum as this is not a usual use case.

Best regards,
-Ivan Salazar
Applications Engineer