Dear
I use LTC2508-32 ADC, VDD=2.5V, OVDD=3.3V, RDLA=0. At this time the SDOA output waveform is very strange, the binary conversion value is not correct, what is the reason?
The following are some schematic diagrams and waveform diagrams
Hi Timsen ,
I have few concerns in your query:
1) I noticed that you are using the correct supplies for Vdd and Ovdd. What is your Vref? Also, is RDLA already tied to ground before initializing the device? Can you try letting the Vref and Ovdd to be in their settling state before putting signal at the analog input? As you can see here, analog input pins are dependent on Vref. So, you need to power up first the Vref. After that, power up the Ovdd as the digital pins are dependent on it. Then let them settle first before putting signal to the analog inputs. Can you send a photo of the waveform after performing the power up sequence? If problem still persist, see no. 2.
2) Are you using a custom board? I have noticed that you used 30.1R to its input. But on its existing schematic, they used 10R and 0R.
3) I also noticed that you are using two LTC2508. If it is okay for you, can you show us the whole schematic?
Thanks and regards,
Jo
Dear
Vref=5V，RDLA=0，Vref and Ovdd to be in their settling state. The resistance has been changed to used 10R.
But the SDOA waveform is still strange, and the converted data is also wrong?
PDFSee attachment for schematic diagram
Dear Jo:
Fixed, because three LTC2508-32 pin 1 RDLA tablet selection problem, initially two LTC2508-32 valid, has been corrected.
Another issue: for pin 14 SYNC of LTC2508-32, the specification says that SYNC should be completed in one MCLK cycle. But MCLK is 1M, the time between two MCLKS is 1us, the falling edge of DRL is almost 650ns, MCU triggers the interrupt, and then pull the high level has passed 1us. What do we do with this? What is your suggestion?
