You can use the MAX35102 without a 32.768kHz crystal, but you must then supply an external 32.768kHz clock signal to the device. This clock is used to provide event timing for the MAX35102.
Refer to the VIH32KHX1 logic levels in the Recommended Operating Condtions table as well as the recommended 32KX1 and 32KX0 pin connections in the Pin Description section in the MAX35102 datasheet.
If you are using the Calibrate Command, the use of a crystal or a highly accurate 32.768kHz clock source is important. The system should function correctly if the 32.768kHz frequency isn’t exact, but we recommend staying within 5% of the nominal 32.768kHz frequency so that all system timings behave as expected and explained in the datasheet.