Dose LTM2893 suit AD7983?

Hello QI,

  The AD4000 family should work with the LTM2893.  I've successfully operated the AD4003 with the LTM2893. The AD4003 is an 18-bit 2Msps SAR.  

  You'll need to operate the AD4003 in the chip-select 3-wire with busy indicator mode and configure the LTM2893 to use a 100MHz SCK2 frequency, 1 word count and a 20-bit word size.  Note that the valid data is in the lower 18-bits.   Here's an example circuit to illustrate the connections between the AD4003 and LTM2893.

Eric

Hello Eric

Sorry for reply later, Your information is very helpful for me, and thank you very much!!

best regards

QI

Hi Eric

Thanks a lot for your information about  AD4003+LTM2893.

Could you have any information about whether AD7983 is compatible with the LTM2893,  i am considering using AD7983 with LTM2893 because i have used AD7983 in my prototype design.

and so I checked the following requirements in datesheet for LTM2893.

・6.25MHz ≤ SPI shift clock maximum frequency ≤ 100MHz

・Operates in SPI mode (0,0): SCK starts low, data captured on rising edge.

・Meets setup and hold timing requirements (tHDMISO2 and tSUMISO2) with the SPI shift clock operating between 6.25MHz and 100MHz.

・SPI shift clock (SCK) is static outside of CS (the ADC does not require a constant running SCK as a conversion clock) ・If used, the conversion start pulse width minimum is ≤ tCNVH

and now  i  want to use 50MHz clock for AD7983.

can  LTM2893 work well with AD7893, Do you have any idea?

Best ragards

YQ

Hello YQ,

  It might be.   If it is, it will operate in a similar manner as the AD4003 – CS\ mode, 3-wire with busy indicator.  (note that the 47k pull-up resistor shown in fig 28 and 32  of the AD7983 data sheet is too large.  It needs to be closer to the 1k shown in the AD4003 example above.)

  I’ve got an AD7983 on order and will try hooking it and an LTM2893 together on my bench and let you know what I find out.

Eric

Hello Eric

Thanks for your advice!!

If you got any information on your bench test, Please let me know. 

Actually, Now i am using AD7983 in CS/mode,3-wire without busy indicator, As you say, it should be changed.

Best ragards.

YQ

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

Hi Eric

Thanks very much!!!

Your news are really good news, and the information are very helpful to me.

Please let me ask if i have a trouble.

Best regards

QI

You’re welcome and I’m happy to help if you’ve got further questions.

Eric