[christianw.]

For reference:

Zitat:Dear Matthew,

thanks for the reply,

to answer you questions i will do via inline quoting.

To clarify what we are speaking about:

Board1 is the board with the chip which failed to death.
Is has the 1206 100nF C11/C12 at all time. /SHDN is done via voltage divider. Bulk-capacity is 2x47u LowESR.

Board2 is the board with the chip which showed the wires startup behavior. Is now has the 1206 100nF C11/C12, changed from 0805 100nF. /SHDN is now done (fixed from C pullup ) via voltage divider. Bulk-capacity is 2x220u LowESR.

This is the board i measured and showed you the images.

All further things belongs to Board2.


> | I am glad to hear you found the supply issue. Now that you have
> | replaced the bad supply bypass capacitance, do both boards show a
> | smooth supply ramp up during power sequencing (a small spike when
> | the device comes out of shutdown may be normal)?

Well the spikes might be due to the bulk capacitance? (2x220u)


> | As to the units being damaged during sequencing, was this
> | occurring on all boards or just board 1 (the one with the bad
> | bypass). Are units only damaged during power-up, or does it
> | sometimes happen during normal operation (IE the device is
> | running normally for a long time and suddenly dies)?

The damage happened to board1 and some other boards. We did several to have one for each student in our group. The damage always happened on powerup with either a loud "clicking/pumping" sound coming from the speakers or having a full DC on the speakers. It never happens on the long run. We also had the phenomenon that only one channel fails, while the other still runs okay for some time. (So there were no load connected on the failty output)

What makes me thought-provoking is, that the short-circuit and/or thermal-protection never kicked in when this happens. So the output-stages wont get disabled.

One thing that come in my mind is, that running the IC in SSM (670kHz +/-7) results in some desync which results in a shoot-through.


> | I am a bit confused by this statement:
> | "When having no load connected, the output spike-swing is as
> | twice as high as with connected load. (24V vs. 12V)"
> |
> | The class D switching waveforms (the high frequency carrier)
> | should switch from GND to VDD (12V in this case). When you say
> | 24V versus 12V - I assume your speaking differentially.

Yes thats right, i meant differentially.

> | Is the
> | signal amplitude (the actual audio) or the switching amplitude
> | (carrier) varying? Do you have any scope shots of the behavior?
> |

I'll attach 2 images of this. There were no audio connected as well as no load (speakers)

> | Also, are you using an output filter (in addition to the load) or
> | are you operating "filter-less" to the load? What precisely is
> | your load (not shown in the schematic but stated to be 8ohm).

The IC is running in a filterless configuration. Speakers are stated as 8ohms. (2way with internall crossover)

> | What is the effective inductance of the speaker load, what is
> | your output filter/zobel (if any), and what is the cable /trace
> | length to the load (etc. any additional relevant information
> | could be helpful).
> |

Cable length is about 60 centimeters. The effetive inductance is unknown, i don't have any equip to measure this, esspecially over the full frequency-range.

> | Please clarify exactly what conditions and when the failures are
> | happening and on which board(s). If possible, clarify exactly
> | what the remaining problems are (if any) that you'd like some
> | assistance or advice on so I can assess how best to proceed.
> | Also, if possible, please continue to operate using a voltage
> | divider based enable for the shutdown pin for the duration of
> | this debug (I understand the other solution may work, but I want
> | to limit the number of differences between your circuit for debug
> | and the standard operating circuit).

Thats mainly "all" problems, but i mean it is a big problem. I need to state that one IC is also failed while no load where connected. We just noticed this by the current-limiter in our PSU.

As for the MAX9709 there is no problem so far, no fails even on 100% workload.

-----------------------------------

Thanks for your patience, i really appreciate your support and service policy.

Kindly regards,


Christian W.