TAS2770: TAS2770 IC : Power Pins Short circuit issue

Hi,

for 1) can you please elaborate on the issue that you are having here? the VBAT and AVDD are being shorted to GND, is this some kind of fault protection? please clarify

for 2) no series cap is required, if EMI is a concern a series 120 Ohm Ferrite bead and shunt 1nF capacitor can be used

Regards,
Arthur

Hi Arthur,

1. Basically when i am checking the resistance between the VBAT and AVDD line to ground. It is short circuited in the IC. This occurred during testing of the IC. 

2. Regarding the series capacitance, when I am placing a series capacitor in the P line of the speaker I can observe a change in the output audio. Also I have doubt that whether the speaker is causing the short circuit in the IC power lines

Hi thirugnanaraman

is it possible for you to provide the layout files for me to review? from your description it sounds as though the device is still functional but it is drawing significant current from VBAT and AVDD supplies. is that correct? on a board which has no TAS2770 IC populated are the supplies shorting to GND? or have you verified that it is shorting through the IC.

When the supplies are applied to the shorted device is the device getting very hot?

we certainly do not require, nor recommend a series capacitor on the output of the amplifier. 

Regards,
Arthur

Hi 

Thanks for the input regarding the series capacitor. I shall update the same over the design.

Regarding the layout, I cannot provide the layout file as it a product and we have NDA with customer.

Also  i have verified that the short is happening through the IC. When I removed the IC from the board, the short in the board is removed. I also checked the IC pins and short is present. In one IC short is between VBAT and GND and In second IC short is between AVDD and GND.

This sounds like these two ICs have been damaged. what is the voltages of the VBAT and AVDD supplies? Is there any ripple on these supplies which could be exceeding the devices absolute maximum ratings, Is the SDz pin being held low until all supplies are present?

regards,

Arthur 

The Voltage of VBAT is 12 - 14.4V and AVDD is 1.8V. The 12 -14.4V is the main source rail and delivered from RPS and the SD pin is having a physical pulldown resistor. The 1.8V for the IC is supplied from  the DC DC switchers. I have measured the ripples and they are in the allowable limit of the switcher.

This all sounds OK, as long as AVDD is not exceeding 2V and 18V for VBAT then it will not risk damage to the device.

If the supply is shorted to GND then I can only think the device has been damaged. 

Regards,
Arthur

Hi Arthur

The AVDD is provided for the processor. The VBAT is given from a RPS. So the voltage surge or over voltage is not possible I think.

but still the IC is short because of some operation. I just want to know what kind of things that can cause them and what are the measure to implement to avoid these things

Hi Thirugnanaraman,

I have sent you a friend request so we can discuss over private message. Is it possible for you to share the schematic section related to TAS2770 and I can review it? 

Understand that the over voltage in the system is unlikely. perhaps check once more during power up/down and see if any transients are occurring during that moment? 

it is also possible that a ESD event could cause this. - did the short circuit happen immediately after populating the amplifier IC or was the board functional for some time before the short occurred? 

Regards,
Arthur

Hi 

Ok I will check the transient one more time. but In our design we have implemented the EMI and ESD filters and A E-fuse in present in the VBAT line. More likely these can avoid the transients. 

All the IC are working fine after population or assembly. It is observed during the working. Mostly during the audio playing scenario.

For the ICs which are shorted are they still able to play audio? do you mean the short will only appear during playback, but in idle mode there is no short?

The ICs are shorted and damaged permanently. This damage is occurring during playback.

No

Hi Thirugnanaraman,

All I can offer here is to review the schematic and layout files if the customer is willing and we can make sure there is no issues in the design.

Regards,
Arthur