tda7498e

Hugh Worrall · ‎2018-01-28

Posted on January 29, 2018 at 05:48

I've just managed to blow up 2 TDA7498E D Class amp chips when testing the first run of 25 production boards. This is the first time we have managed to damage any chips in over a year of prototype testing.

We are using the chips in mono mode and have the left and right outputs tied together as per the datasheet (Mono mode is selected by connecting the mode pin 31 to VDSS pin 26).

The damaged boards have the four VCC (+35V supply pins) blown off the chip (see attached photo). The chip blows when audio is first output during one of our factory tests (you get a small bang and a puff of smoke).

I can get the same result by putting the chip into stereo mode by floating the Mode pin and playing audio (this causes the left and right amplifier outputs to short each other out). I also noticed that when the chip is in Standby the VDDS supply is turned off (e.g. at 0V).

What I think may be causing the problem is taking the chip out of standby with audio present on its audio input as follows:

1.

Put chip into standby mode (VDDS supply is off and at 0V, so Mode input is in â€˜Stereoâ€™ state).

2. Apply external audio signal to the INPA pins

3. Take the chip out of standby

I assume as the mode pin is initially at 0V the chip powers up in stereo mode and then switches to mono mode when VDDS supply >2.5V. If the audio amplifier starts playing before the chips switches to Mono mode the output stages short out. I also assume if you power up the chip with audio present it will also blow.

Could STM confirm that powering up the chip or taking the chip out of standby with audio present on its input (with the chip configured for mono operation) is causing the chips to blow, or what is the likely cause.
What the recommended power up and standby sequence is when using the chip in mono mode (e.g. Mute chip for x seconds before powering up the chip or taking it out of standby etc).

Regards,

Hugh

JCI NZ

Hugh Worrall · ‎2018-02-01

Posted on February 01, 2018 at 23:58

After several days of testing a a pile of blown chips I can confirm that if you switch the standby signal with the chip configured for mono mode with audio applied to the chip the chip may be destroyed. I ran the following test:

Chip configuration:

1. Mode pin tied to VDDS (mono mode),

2. OUTA and OUTB pins wired in parallel as per data sheet

3. Supply voltage set to +35V

Test Procedure

1. 1khz signal applied to the chip INPA input, output level set to about 80%, no output load

2. Standby signal activated

3. Wait a random time period between 1-4 seconds

4.

Standby signal deactivated

5. Wait a random time period between 1-4 seconds

4. Go to step 2 above

Typically the chip blows within 10min. You can repeat the test with the mute signal and the chip is fine (I left the test running for 12 hrs with no damage).

I now running the following test:

1. 1khz signal applied to the chip INPA input, output level set to about 80%, no output load

2. Mute signal activated

3. Wait 1 second.

4. Standby signal activated

5. Wait a random time period between 1-4 seconds

6.

Standby signal deactivated

7. Wait 1 second.

8. Mute signal deactived

9. Wait a random time period between 1-4 seconds

10. Go to step 2 above

This test has been running for over 1 hour with no damage to the chip so it looks like if the chip is muted while taking the chip in and out of standby it works ok. I have no idea at this stage how long you must wait between changing the mute and standby signals (currently 1 sec in my test above).

In general I've found the ST documentation very poor and ST give very little detail on the various signals including Diag, Mute, Standby, Synclk and Rosc. No details are given on the required resistors on the mute and standby pins shown on the example circuit. I latter found out (via an ST engineer) a resistor value of at least 30k is required to guarantee its operation. No mention is made of the capacitors (e.g. are they required and if so what are they for and what is the min and max value?).

Note I'm yet to have a reply from ST via the community, their technical support website or via Braemac so it seems the ST technical support is as bad as their documentation. A pity as the chip otherwise has performed well. I will thing twice before using any other ST parts.

Regards,

Hugh

gianni gianni · ‎2018-02-02

Posted on February 03, 2018 at 07:40

Hi Hugh,

many thanks for your investigations !

I wonder if, operating in stereo mode, keeping MODE pin always tied to GROUND, thereâ€™s still the risk to blow the chip when switching on with music playing.

Just to know if the vulnerability you found is still present when running the chip permanently in stereo mode.

Best rgds,

Gianni

Hugh Worrall · ‎2018-02-04

Posted on February 04, 2018 at 21:35

Hi Gianni,

Should be fine in stereo mode. In mono mode the L and R outputs are connected in parallel and if they are not in sync with each other they will short each other out.

I ran a test where the amp was put into mute about 100msec before putting it into standby, then unmuted it 100msec after taking in out of standby. Each cycle was about 5sec on average. It ran for over 2 days with no issues so this seems to fix the problem.

E.g. in mono mode do not change the state of the standby signal unless the mute signal is active.

Cheers,

Hugh

gianni gianni · ‎2018-02-05

Posted on February 05, 2018 at 21:16

Ok Hugh, so I will stay away from mono mode (enough power for me in stereo mode) and I should be safe ...

TDA7498E

was my favourite chip because I liked the native BTL design to avoid bus pumping but, at the same time, I was a little bit worried about some reports of sudden failure.

Now I understand that many people use this chip in mono mode and maybe the most likely cause of all these failures is about the problem you have discovered.

Many thanks again !

g.

hhose · ‎2019-01-17

hello.

according to datasheet TDA7498E operating temperature is 0-70 C.

How does working this IC working under zero?

does it go destroyed?

_________________________________________________________

Hugh Worrall · ‎2019-01-20

Hi,

When have run the at -5C with no problems. They don't like powering up into full load at -15C.

Regards,

Hugh

Hugh Worrall · ‎2019-01-20

Opps, that should have been:

We have run them at -5C with no problems. They don't like powering up into full load at -15C.

Regards,

Hugh

ACave.1 · ‎2022-01-25

Good afternoon community I was using the TDA 7498E integrated circuit in stereo mode it worked well. The problem appeared when I wanted to use it in mono mode when activating the circuit it burned the TDA7498e. It remained integrated and I analyzed the datasheet. I test the components apparently it was only to change the TDA7498E which I did and burned again. I would like to know if something similar happened to someone since I am grateful.

JYAZB.1 · ‎2023-05-16

Hugh,

ST answered you about this problem? My engineering team just reached the conclusion that the chip was blowing by itself and they just found this post. Your analysis of the problem is 100% correct. Nice work!