What the REF1004I-1.2/2K5 is and where it fits
The REF1004I-1.2/2K5 is a precision shunt voltage reference from Texas Instruments, delivering a fixed 1.235 V output with ±0.3% initial tolerance. It comes in an 8-SOIC surface-mount package and is part of the REF1004 family of low-drift references. As a shunt reference, it behaves like a two-terminal Zener — you bias it with a resistor from the supply, and it regulates the voltage across itself. That makes it dead simple to drop into an existing rail: just one resistor and a bypass cap, no feedback loop to stabilize.
Key parametric decisions for your BOM
For a 12-bit ADC with a 2.5 V reference, that's under 1 LSB, so it's fine for most industrial sensor chains. That's low enough for a 10-bit or 12-bit system but might be marginal for a 16-bit SAR ADC without averaging. The shunt can sink up to 20 mA continuous, and the minimum cathode current is just 10 µA. That wide operating range means you can bias it with a high-value resistor for low-power battery circuits, or push it to 20 mA for a strong reference bus.
Lifecycle and compliance
The bulk package (tube or tray) is typical for engineering samples or small-run production. For reel quantities, check the alternate order codes in the same family.
How it compares to the LM4040CIM3-3.0/NOPB
The LM4040CIM3-3.0/NOPB is another shunt reference from TI, but it's a 3.0 V device with ±0.5% tolerance and a 100 ppm/°C tempco — five times the drift of the REF1004I-1.2/2K5. The REF1004's lower drift and tighter tolerance make it the better choice if temperature stability matters more than output voltage level. Both come in surface-mount packages, but the LM4040 is available in SOT-23 (smaller footprint) while the REF1004 uses the wider 8-SOIC. If board space is tight, the LM4040 wins; if you want the lower drift, stick with the REF1004.