Hi there,
I'm having a little trouble with the DAC128S085 that maybe someone else has seen before. It seems that the DAC is driving some voltage into the serial pins for the first couple of clock cycles. I am also not seeing any of the expected voltages from the analog output pins.
Does anyone have any idea what is happening?
My setup is as follows:
1. DAC is on a DIP adapter into a breadboard. I have checked impedance between header pins and SOP legs and found no short circuits.
2. I have inserted 100 ohm resistors between the uC and the DAC (although this was not originally the case).
3. VA is 3.3V and decoupled to ground by a 33 uF (!) cap. Va is tied to both reference voltages
4. The serial bus is being driven by an Atmel UC3 also running at 3.3V (and powering the DAC).
5. If the power supply to the DAC is removed, or the DAC is removed from the breadboard then the SPI voltages are nice sharp square waves.
6. There is nothing else on the breadboard.
7. If I vary Vref with a potentiometer, Vout moves up and down as expected but is not impacted by writing to the register.
Serial clock (blue, 1MHz) / data in (yellow, 0x0AAA)
Data in (yellow) / chip select (blue)
Data out (not expecting any output as CS is low for 16 clock cycles)
Vout1 (yellow) / chip select (blue)