I'm trying to set up a board using a DAC61401.
My schematic is as attached. I already noticed that DVDD is propably to low.
But this voltage seems to be part of the Problem.
VDDA = +12V
VSSA = -12V
VDDIO = 3,3V
I am providing data via SPI with 3,3V and 7,5MHz generated by a TMS320F28032PAGT with 47Ohm series resistors.
Configuring the DAC with 10V Range, I see that at approx 8V output level the Signal suddenly jumps.
With the range beeing +/- 5V the point where the distortion kicks in also reduces to approx 4V.
This can be seen in a simple sawtooth or a sine.
Delivered data has been checked with SPI decoding via scope (LeCroy HDO6104)
Data read out via probes:
Configuration is for the moment the one noted from the datasheet:
Adr 0x03 -> 0A 04
Adr 0x04 -> 00 00
Adr 0x09 -> FF FE
Adr 0x0A -> 00 05 (for +/-5V range)
Schematic:
I already noted, that DVDD is only 3,3V. I suspected this to be my problem. So I've added a 5V source and provide 5V to DVDD (Pin 20).
IOVDD (Pin 17) remained at 3,3V. This was verified multiple times!
I saw now, that with 5V on DVDD no output was provided anymore. Even V.ref remained low. I suspected the IC to be broken maybe, so i replaced it but the situation did not change.
I decreased the DVDD (Pin 20) again to 3,3V and the DAC started to operate again.
I provided DVDD (Pin 20) from an external source now, and started with 3V3.
The DAC showed the distortions as discribed above.
I increased DVDD now (and only DVDD - IOVDD remains at 3,3V) the distortion moved up linearily to the increase of DVDD. At approx 4,0V the output signal got distorted in a different way. It seems, that data gets misinterpreted now. At 4.2V the DAC output got frozen. Reducing DVDD again below 4V the Data was updated again.
According to the datasheet the SPI level should only depend on IOVDD.
But it seems to me, that also DVDD has an impact on the SPI Logic levels.
Could this be?
Any clue what this kind of distortion could cause?
