Go Down

Topic: Do not follow Simple Audio Player example - DAC0 now non-functional on DUE (Read 13 times) previous topic - next topic

stimmer

I'm still confused as to how exactly we have blown these up. Technically there is only one DAC, it is multiplexed to two sample/hold buffers. So somehow we must have blown the last output transistor. Yet the pin still works fine for digitalWrite/Read. Personally I'm waiting for the Due to be more widely available, then I was going to try overloading DAC1 in a controlled way until it breaks too, to try and find where the limits are.

Incidentally by my calculation it should be possible to get 11 bits at 41kHz from the PWM hardware, and that has 8 channels :D

Grumpy_Mike

Rather than blow one up which tells you little why not look in the data sheet.
The problem with a distruction test is that it tells you nothing of the situation where it still works but damage is being done so that it has a reduced life time.

chriskner


Rather than blow one up which tells you little why not look in the data sheet.


The SAM3X/A datasheet:
Page 1369:
45.5.3 Conversion Performances

  • For performance and electrical characteristics of the DACC, see the product DC Characteristics
    section.



Page 1391:
46.2 DC Characteristics
I(OH) (ISource) for pins in Group 2 (which include the DAC), is -3mA.
I(OL) (ISink) for pins in Group 2 (which include the DAC), is 6mA.

Pins in Group 2:
PA[1-6], PA8, PA[10-13], PA[16-17], PA[20-24], PB[4-7], PB9, PB[12-13], PB[15-21],PB[25-31],PE[10-14], PE16, PE22,
PE24, PE26, PF[3-5]

Group 1 (most other) pins have limits of -15/9mA.


The minimum allowed load (by spec, conservative) is 3.3V/.003A =1100 ohms.  Personally, I would never intentionally come close to this low of a load for this chip.

The information in this thread: http://arduino.cc/forum/index.php/topic,132130.0.html applies to everyone, even us audio guys.

-Chris
(not an audio guy)

Markus_L811


DAC0 is the one you learn on, DAC1 is the one you then take care of.

Duane B


destructive testing  :~

stimmer



I(OH) (ISource) for pins in Group 2 (which include the DAC), is -3mA.
I(OL) (ISink) for pins in Group 2 (which include the DAC), is 6mA.



That is the spec for the digital output stage of the PIO pins, not the analog stage of the DAC. (They are the maximum loads for the digital output to reach a specified voltage level at a specified speed - not the absolute maximum current)

What I'm looking for is some specification of output impedance or output resistance (ie the minimum resistance on the output so that the output voltage is still accurate to 12 bits without distortion) - usually called RL or RLOAD or Z

I've looked and looked through the SAM3X datasheet for the specifications for the DAC and they are missing. But I think I may have found something useful. The SAM3S datasheet has a section on the electrical characteristics of its DAC which is mostly the same as the SAM3X, except that it also includes a table on analog output specifications (on p1033), which gives RLOAD as minimum 5k ohms. Given the similarities I shall assume this is true for the SAM3X too.

http://www.atmel.com/Images/Atmel_6500_32-bit-Cortex-M3-Microcontroller_SAM3S_Datasheet.pdf

Go Up