Hi Sir, We have designed the reference board using LTZ1000A,now the board works normally.But when we did temperature testing in the chamber,we found LTZ1000ACH TC is 7times bigger than noted in the datasheet.Plz refer to below pic.External resistors for temperature setting is 12.7K and 1K respectively.Both two resistors TC is 2ppm max.We tested from the temperature from 0C to 40C, the 7V reference voltage changed more than it normal?the datasheet noted its TC is only 0.05ppm.Plz advice.Many thanks.