At power-up, my LTC2668 initializes all channels to 0V. That's correct by my setting of MSP0 = 5V, MSP1 = 5V and MSP2 = 0. According to Table 4, that selects 0-10V operation with initial outputs at 0V. This condition persists for maybe several seconds, then the DAC switches to driving 5V at all outputs. CS#/LD is pulled up to OVP, but the other SPI pins are floating. CLR# is also tied to OVP. The power supplies are steady at the time the output voltages change.
Is there any chance the DAC could be changing this on its own in response to a problem? Thanks.
Can I see a schematic and layout? What do you means the SPI lines are floating? They should be tied to something. How are the MSP pins controlled?
Here is the schematic. The SPI lines are usually controlled by another board. I was doing a "smoke test" before attaching the other board. I tied CS#/LD to 3.3V to OVP to prevent unintended SPI interaction. My tech looked and found a solder problem on the board. Once fixed, the 2668 powered up with all channels at 0 as I intended.
Great, If you have any other questions or problems, let me know.