DAC1220: Unstable working

Oleg Kolomenskiy

Prodigy 30 points

Part Number: DAC1220

Hello,

i can't find out decision, that's why i have to ask.

Our problem: DAC1220 unstable working.

What we have:

Fxin=2.5Mhz

Fspi_clk=200kHz

20bit mode, C1=10nF, C2=3.3nF.

DVdd=5Vdc, AVdd=5Vdc, they were created with difference linear regulators.

DGnd and AGnd connects with 0R resistor near DAC1220.

We’re write 0x0000 or 0xFFFF data to DAC1220 via SPI (master is F28M35H52C1RFPT Texas Instr.).

Reference voltage = 2.5Vdc. The output voltage must be 0 to 5V.

We have mostly stable output signal at frequencies under ~7Hz (sometimes it breaks):

SPI data:

Then we trying to increase analog output frequency and signal breaks:

SPI Data:

Is this problem related with settling time? Can DAC1220 answer by spi in process of settling time?

What should we do to make stable working of DAC1220?

Problem: DAC1220 unstable working.

over 5 years ago

0 Paul_Frost over 5 years ago

TI__Guru 53923 points

HI Oleg,

This is an interesting problem. Can you confirm that if you stop reading immediately after a write command does the output looks better?

Thanks,

Paul

0 Oleg Kolomenskiy over 5 years ago in reply to Paul_Frost

Prodigy 30 points

Hi Paul,

yes, first we worked without read operation, and when we got problems, we started use read command.

0 Paul_Frost over 5 years ago in reply to Oleg Kolomenskiy

TI__Guru 53923 points

Hi Oleg,

I do not see anything specific in the datasheet that is being violated. Can you try an experiment? What happens if you increase the CS-high time between the read and the write command? Try 50µs.

Does it make any difference?

Thanks,
Paul

0 Oleg Kolomenskiy over 5 years ago in reply to Paul_Frost

Prodigy 30 points

Hi Paul, good news - we have sucsess with all 3 DACs)

Key for sucsess:

-SCK with "pull down" when CS not active (not "pull up" with OR IC)

-200ms delay after start up, before reset procedure (it is strange because all power supplys give 5V for 5ms, reset not applied sometimes)

-independent reset, independent self calibration for all 3 DACs with reading status of self calibration

Thank you!

Data converters

Data converters forum

DAC1220: Unstable working