Other Parts Discussed in Thread: REF3125, DAC7551
Hi,
I am working with the DAC7551-Q1. Attached is the datasheet: https://www.ti.com/lit/ds/symlink/dac7551-q1.pdf?ts=1592428323142&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FDAC7551-Q1
The end goal is to have the DAC output a 65KHz sine wave. The only signal being seen on the DACs output (Vout) is a ~.5V DC signal.
The DAC is communicating with a Teensy 4.1 development board using the SPI interface; The DACs input clock is running at 4MHz. The DACs Vdd and the IOVdd pin are tied together and are receiving 3.3V from the Teensy 4.1 development board. The Vfb pin is tied to the Vout pin. Currently, the VrefH pin is tied to 3.3V on the Teensy 4.1. I understand that I will eventually need to provide a buffered reference (REF3125), but I am hoping using the Teensy 4.1 in the mean time is not causing any issues. Currently there are no bypass capacitors in place, but I would assume that I would still see a sine wave on the output even if it is a bit messy.
According to page 13, section 7.3.3.3 of the datasheet: "On power up, all registers are cleared and the DAC channel is updated with zero-scale voltage. The DAC output remains in this state until valid data are written." Since this is the case, why am I seeing a ~.5V signal on the output of the DAC on power up? Also, according to section 7.3.3.5 the output is set to zero-scale voltage immediately after the !CLR pin is brought low I should see zero-scale voltage, which I don't believe I am, unless I am not understanding zero-scale voltage (seeing ~.5V).
On page 14, section 7.5.1.1 of the datasheet it says that the !SYNC pin acts as a frame synchronization signal and chip enable. Currently, the !SYNC HIGH time is set to 10ms and is only asserted once before the first word. Do I need to be continuously asserting the !SYNC pin after each word or just once before the first input word?
Any help, comments, or example code will be greatly appreciated.
Thanks,
-Alex