reference
I've been looking for a 3V ±0.1% reference in a SOT-23 package to replace my current ±0.5% solution of a TL431 and about 5 passive 0603 components.
At the moment I've found LM4040A30 which is $1 at 1ku, and comes in a SOT-23 package. It also requires a 0603 resistor, but is stable without a capacitor.
I'm wondering if anyone has any better solutions. Even more awesome would be something like an ultra stable precise zener diode in 0603 or 0805 size.
The datasheet of the AD7176-2 is pretty careful to always refer to specific pin names, like AVSS or AVDD, rather than just generically talking about "ground".
For example, when they talk about the input voltage range (p. 4), under the line "Absolute AIN voltage limits", they give the min limit as "AVSS - 0.050" and the max as "AVDD1 + 0.05". Similarly when they give the "Absolute Reference Input Voltage Limits" (p. 5), they give the same limits. As long as you obey these limits, the chip should work as advertised.
In particular, if your AVSS is -2.5 V, then REF- of -0.5 V is within the limits.
That said, if you can get the attention of an Analog applications engineer (like if you are doing this for a commercial project or at a university), it wouldn't hurt to show them your final design before sending it out for fab.
You assume correctly - you decide on the voltage regulation point (volts), subtract that from your power supply voltage and use the difference voltage and a resistor to set the operating current.
Take into account how much current flows through the other resistors too (if using them): -
Best Answer
I think the LM4040 is the way to go. I don't know of any "pre-biased" shunt diodes, and if there were they would likely cost more and you would have to weigh that against the scant space savings.
If you can ease up on the 0.1% to 0.2 (B-grade) or 0.5 (C), the prices seem to drop quite dramatically.