Part Number: DAC8820EVM
The board just arrived, I power the board as is described in the manual +14V +VA, -14V -VA, +5V DVDD. Jumpers in the default position.
IC U2 start to heat over 50C.
After a few seconds, the output, Ref, +VA and -VA start to oscillate.
Kevin DukeDAC Applications Manager
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In reply to Duke of DACs:
I appreciate your fast and detailed response. To answer your questions.
Just to confirm, because sometimes unexpected things happen with the EVMs in manufacturing etc., could you send a photo of the jumper configurations for a double-check?
Sorry for the bad quality picture.
How much current is being drawn from the +14V, -14V, and +5V power supplies?
(+14V,~120mA) (-14V,<10mA) (+5V,<10mA)
The +5V DVDD connection I assume is being provided via J5.10 with W3 in the 1-2 position? Is anything supplied on J5.9? Though maybe unused by the DAC depending on the configuration of W3, the 3.3VD rail is still used by the supporting components which drive the digital interface to the DAC8820.
It's correct, the +5V DVDD is provided via J5.10 with the W3 in the 1-2 position as is showed in the picture. I notice now that 3.3V is the power supply for ICs U6, U7, U8, and U9, the 5V is not re-direct to them, is need it? If I want to drive the DAC, this components should be power up, no?.
It would also appear that the EVM was designed with a larger capacitive load than the INA105 is rated for, so one suggestion would be to uninstall C7 to see if that removes the oscillation issue you have observed.
Removed C7, no improvements. The magnitude of the oscillations, (-VA, 71mV@PkPk)(110mV@PkPk)(REF&Output, 61mV@PkPk) In the REF and output the oscillations have a well define sinusoidal oscillation of 200 kHz, the rest is very random.
U2 getting hot would not add up to me with the default jumper position having W1 shorted in the 1-2 position, therefore effectively leaving U2 with no load in a simple voltage-follower configuration.
I have the same thought so I check for shortcuts and everything appears correctly wire up, as is in the schematics.
I have to add a couple of things:
In reply to Ivan Benzaquen:
Thanks for following up.
Ivan BenzaquenIt's correct, the +5V DVDD is provided via J5.10 with the W3 in the 1-2 position as is showed in the picture. I notice now that 3.3V is the power supply for ICs U6, U7, U8, and U9, the 5V is not re-direct to them, is need it? If I want to drive the DAC, this components should be power up, no?.
Correct - without providing the 3.3V supply the parallel interface will effectively be inaccessible, therefore you will not be able to drive the DAC from your host controller.
If I touch with my finger the IC U2 the oscillations decrease dramatically.
If I connect an external reference source the oscillations disappear, I did not drive the DAC yet, so I don't know if the EVM is fully functional, but the reference source for the DAC is not oscillating, the power lines are not oscillating and U2 is not reaching high temperatures
Maybe one worthwhile test would be simply removing U2 - though I do not currently see any other reason for instability in the design.
When you do the second test with an external reference, I assume J4 is just moved to the 1-2 position with no other modifications to the board?
Removed U2 and the reference start to misbehave. U1, REF102, is only giving 4.17V through pin 6, no oscillations but an incorrect voltage reference for the DAC. Jumpers are set in the default position.
If I resolder U2, the U1 still giving an incorrect voltage in pin 6, the U2 IC is stable, no heating, no oscillations in the supply lines, references or output.
Since bypassing the reference, U1, by applying an external reference kill oscillations and temperature in IC U2 is normal, my conclusion is that U1, REF102 was/is the cause of the problems.
As well I do not understand what was the problem. I resolder the older REF102 and everything works fine again. You must be right cold solder or flux contamination.
I'm addressing the RST through the W6 connector. I've removed the jumper and connect one of the pins to GND with a cable, the pin goes directly to the RST pin of the DAC, and I've checked that the RST is low.
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