I was trying to say: Higher temperature doesn't mean higher power in any case
Let's assume 25°C ambient temperature:
LTZ1000A (55°C-25°C)/400K/W = 75mW
LTZ1000 (45°C-25°C)/80K/W = 250mW
The datasheet states 400K/W and 80K/W (typical) in one place but later includes this graph:
Anybody made any measurements to see which numbers are right? Would those numbers include heat lost via the leads, using a typical PCB layout?
Like Dr Frank, I can't see much, if any advantage to the LTZ1000A for meterological applications - there's nothing to stop you adding more insulation to the LTZ1000 to match the A version but not vice versa. IE. you have no choice but to use a higher minimum operating temperature above ambient, 10C, than the 2.3C (or 5C?) of the LTZ1000. The LTZ1000 is quite a bit cheaper to boot.
There has been some discussion that the A version suffers from less hysteresis but I can't recall if was just conjecture or real.
Ironically, to minimize power consumption you need to set the operating temperature as high as possible to allow the maximum amount of insulation to be used, and still maintain regulation at the highest ambient temperature. The heater power required at lower ambient temperatures is thus reduced because of the improved insulation levels.
Eg. assuming Tambient max = 38C, min = 10C and zener dissipation is 29mW (7.2 x 4mA)
Operating temperature = 55C, max thermal resistance allowed (Rth) = (55 - 38)/.029 = 586K/W. At 10C ambient, heater power = (55 - 10)/586 = 77mW.
Operating temp = 100C, max Rth = (100 - 38)/.029 = 2138K/W. At 10C ambient heater power = 42mW. Achieving 2138K/W may be a bit of a challenge with the non A version however.
Operating temp = 43C (LTZ1000 only) max Rth = 172K/W. Power @ 10C = 192mW.
The advantage of the A version here is perhaps that Rth is specified and presumably doesn't vary much (but not specified of course!), whereas characterising your own design insulation, and more importantly manufacturing it consistently enough may be quite tricky. So for applications where long term drift is less important than power consumption, and the volumes are too high to characterise individual units but too low for significant thermal design and characterisation expenditure, the A version may be better.