Hello everyone
I want to use LTM2893 to isolate SPI I/F for AD7983, is AD7983 compatible with the LTM2893?
On the datasheet of LTM2893, It is mentioned LTM2893 is optimized for isolating 1Msps high resolution 18-bit SAR ADCs, but these are only some suited legacy LTC ADCs on datasheet.
Do you have any recommended legacy ADI ADCs which can work well with LTM2893?
Best ragards
QI
Hello YQ,
Good news! I have the AD7983 working with the LTM2893 successfully on my bench.
You will need to set the LTM2893’s word size to 18-bits and configure its SCK2 frequency to be 66MHz or lower. Since you are intending to use a 50MHz SCK, you have the choice of setting SCK2 to either 50 or 66MHz. Using SCK2 set at 66MHz vs. 50MHz will shorten the minimum cycle time by approximately 5ns allowing a slightly higher Fsample.
Assuming you’re not using the internal CRC and the auxiliary control lines SA, SB and SC are all directed from the logic side->ISO side, the LTM2893 configuration words are:
50MHz SCK2: 0x20 and 0x84
66MHz SCK2: 0x10 and 0x84
As I mentioned earlier, you’ll need to connect the AD7983’s SDO to the LTM2893’s MISOA2 and BUSY2 and use a 1k pull-up resistor on this line. The AD7983’s SDI should be connected to VIO and SCK/CNV connected to SCK2/CNV2.
In this system, the valid data is the MIDDLE 16 bits.
Here are some scope images showing operation with a slightly higher than mid-scale input with a 50MHz SCK/SCK2 frequency:
Zooming in on the data transfer:
Eric
Hello YQ,
Good news! I have the AD7983 working with the LTM2893 successfully on my bench.
You will need to set the LTM2893’s word size to 18-bits and configure its SCK2 frequency to be 66MHz or lower. Since you are intending to use a 50MHz SCK, you have the choice of setting SCK2 to either 50 or 66MHz. Using SCK2 set at 66MHz vs. 50MHz will shorten the minimum cycle time by approximately 5ns allowing a slightly higher Fsample.
Assuming you’re not using the internal CRC and the auxiliary control lines SA, SB and SC are all directed from the logic side->ISO side, the LTM2893 configuration words are:
50MHz SCK2: 0x20 and 0x84
66MHz SCK2: 0x10 and 0x84
As I mentioned earlier, you’ll need to connect the AD7983’s SDO to the LTM2893’s MISOA2 and BUSY2 and use a 1k pull-up resistor on this line. The AD7983’s SDI should be connected to VIO and SCK/CNV connected to SCK2/CNV2.
In this system, the valid data is the MIDDLE 16 bits.
Here are some scope images showing operation with a slightly higher than mid-scale input with a 50MHz SCK/SCK2 frequency:
Zooming in on the data transfer:
Eric
