Forum Post: ADS 1291 DRDY is constantly high

Dear TI Staff,

I had found some similar problem on ADS1298 that its DRDY constantly high because of wrong power-up sequencing. It was already fixed.

Now, I'm working on new project with ADS1291  and the same problem is happened again. I quite sure it cause from power up sequencing but I don't know exactly what it is.

I tied CLKSEL pin HIGH to use an internal clock, CS pin LOW, and  CLK pin floated. Then followed power-up sequencing. I used t(POR) 50 ms, t(RST) 5 ms, and wait for 100 ms before tied START pin HIGH.

The problem is DRDY pin is not toggling although few seconds later.

I also have figure of power up sequence and schematic of my circuit.

blue line is RESET pin and purple line is DRDY pin. After that, the purple line is always constantly high.

Thanks for your support.

Boonyanuch