I see a very low-frequency noise, 2Hz to 3Hz for example, on the MAX1452 output. What causes this?

The low-frequency noise could be associated with the ODAC and/or OTCDAC outputs. Sigma-delta DACs use pseudorandom sequencing of capacitor charge "dumps" to keep the DAC output at the desired voltage level. Sometimes the DAC sequencing can fall into a pattern. A very long sequencing pattern could repeat and produce output "tones" which can show up on a spectrum analyzer as very low frequencies. Since ODAC and OTCDAC sum directly into the output OUT, these tones could appear on the output. A quick test would be to set up the signal conditioner and monitor the output to see the low-frequency noise, then change the DAC digital value by one or two bits and see if the low-frequency noise disappears or moves to some other frequency. To avoid the low-frequency noise, find the DAC settings that produce them, and avoid those settings in the final calibration of the ODAC table by adding 1 to any "tone value." Being off by 1 bit will make no measurable difference in sensor performance. Please note that Maxim has not been able to produce these tones, but it is a known artifact in sigma-delta DACs.