TAS5825M: Problem with power output PBTL

Trying to outputting over 20 watts generates a dc fault left channel. What is meant by a DC fault ?..

Richard,

How is your thermal design? is there any over temperature warning reported at register?

May you help print all the register information for us to check if anything abnormal.  Also may you attached your schematic.

You say the same circuit output almost 50W, is that exactly the same design, or some small change?

Dylan

The only differences is some smaller caps sizes were used . The other fault and warnings registers report no faults .

I tried to paste in the schematic but it didn't take . Is there a trick

Richard,

You should use insert file instead of simply paste.

Richard,

Our expert will review your schematic and layout, to check if anything abnormal.

Dylan

Hello Richard,

The schematic capture is low resolution so I can't offer much feedback there, could you try uploading a higher resolution image? Also, do you think you can can capture your PVDD waveform and your output waveform at this max output power where you see the issue, and then at a lower output power e.g. 10W, 15W.

Best Regards,

Luis

Luis,

HIRes Schematic  attached. I won't be able to send wave forms until early next week

Hello Richard,

We recently modified our datasheet to change the recommended bootstrap capacitance from 0.22uF to 0.47uF. In low frequency conditions ~20-100Hz, and at high output power close to clipping can cause a drop in BST voltage that could be causing the issue you are seeing. Could you test with the corrected BST capacitance to see if you see if this addresses the issue.

Best Regards,

Luis

Luis,

I will have to order some and give it a try.

Hello Richard,

Give us an update when you get the chance to collect those results.

Best Regards,

Luis

Luis,

Changing from .22uf  to .47uf  did not solve the problem. I have another symptom when the problem occurs. Most of the time above a 20 watt threshold, the amplifier just quits Occasionally, instead of quitting, the amplifier goes crazy and starts producing an output all by itself., even after the input is killed.  

Hello Richard,

Did you get the chance to get the previously requested PVDD waveform and your output waveform at this max output power where you see the issue, and then at a lower output power e.g. 10W, 15W.

Also you mentioned previously mentioned you used some smaller cap sizes compared to your previously request design, can you elaborate more on what the changes were(the previous cap sizes and what was is being used now). Can you also provide the specific components used on your output filter, and the ferrite bead filter.

Best Regards,

Luis

Output Inductor   10 uh Murata DD1274AS-H-100M=P3

Filter Cap .68uf      Samsung CL31B684KBHWPNE

Filter bead          Laird Signal HI0805R800R-10 

Filter bead bypass cap 100pf  Samsung CL10C101FB8NNNC

I will take the wavefform

Hello Richard,

Thank you for the info, will look into it further

Best regards,

Luis

Here are two sets of waveform. Both graphs are of one inductor waveform and the +24V power supply.

First at 19 watts into 4 ohms

Second is after the tas5825 went crazy. This occurred when going over 20 watts.  The following waveforms are with no input signalSUB 19 W 4 OHM .PDFTAS5825 GONE CRAZY.PDF

Hello Richard,

Thank you for the waveforms. Also to clarify the location where you are probing is before the filter? Also what is the power supply being used in this a bench supply or a power source on your system.

You mentioned previously mentioned you used some smaller cap sizes compared to your previously request design, can you elaborate more on what the changes were(the previous cap sizes and what was is being used now).

Best regards.

Luis

5 amp 30 volt regulated bench supply. This is the same supply I have used for all testing.

By smaller cap sizes I meant going from 0805 to 0603 size.

Luis,

You asked  where it was probed , it was right at the output inductor.

Richard,

From the waveform, it looks like output is clipped a lot, that means large output power should be delivered out.  May you probe below points when go crazy, we may understand more from that.

1. both P and N of PBTL output 

2. two BST pins

3. current at PVCC pin.(you can read from power supply)

Dylan

Will do.

Luis,

What is the normal  bootstrap voltage above the PVCC rail? .

Hello Richard,

The normal BST voltage is 5V.

Best Regards,

Luis

Lusi,

At 16 watts into 4 ohm power supply current is .9 amp. Idle current no signal is .195 amps .

Attached is the waveform on of one of the inductors and the bootstrap capacitor. All the bootstrap capacitors(.047uf) and inductors have the same waveform  look the same on both the P and N sides.

The mono  amp delivers  16 watts into 4 ohm with .09 % THD +n @ 1Khz and the amps looks fine until the power amp hits 20 watts. Then   the distortion start climbing and above 20wtts it crashed.

.

Luis,

At over the 20 watt threshold when the device goes hi-z , I get a DC fault left . What is exactly a dc fault and how does the TAS5825 detect it? This is sine wave testing a 1khz. into 4 ohms

Hello Richard,

A DC fault is detected when there is a DC offset seen on the output, so at your high output power condition if you are seeing the abnormal switching output if there is a several issue with the duty cycle mismatch between the outputs than it could generates a DC fault.

Also can you confirm this issue is replicable on multiple boards?

Best Regards,

Luis

Luis,

It has happened on multiple boards. Also I rewired a stereo chip to PBTL on the same board I was testing , and got similar results. 

Luis,

Have you seen this type of problem before ? If so what was the cause?

Hello Richard,

I have not encountered this type of problem before on this device, however I will check with my team. However on devices i have encountered if there instability that causes issues with the PWM switching it can sometimes result in a dc offset.  Can you repeat this test without a load and capture the waveform at the same input level that correlated to the 16W/20W/and above 20W.

Best Regards,

Luis

Luis,

Which waveforms do you want me to capture?

Hello Richard,

The PWM output, the output after the filter, and also the fault line.

Best Regards,

Luis

Luis,

Could all these problem be related to not having the bypass capacitors near enough to the device?

No over current faults.

It is possible that not having the bypass bypass capacitor close enough to the chip could cause this weird behavior  . The .1uf bypasses are 1.8mm away from the chip. Also on the reference design, the grounds of the bypass caps are connect directly to  pin 5 and pin 20 and thru the ground pad underneath the chip. On my layout the bypass caps are connected, to the ground plane and through the vias. 

.