OA1NP Datasheet, PDF (19/31 Pages) STMicroelectronics – Rail-to-rail input and output

OA1NP, OA2NP, OA4NP
Application information
Equation 5
Months = A_F  1000 h  12 months  24 h  365.25 days
To evaluate the op amp reliability, a follower stress condition is used where V_CC is defined
as a function of the maximum operating voltage and the absolute maximum rating (as
recommended by JEDEC rules).
The V_io drift (in µV) of the product after 1000 h of stress is tracked with parameters at
different measurement conditions (see Equation 6).
Equation 6
V_CC = maxV_op with V_icm = V_CC  2
The long term drift parameter (V_io), estimating the reliability performance of the product, is
obtained using the ratio of the V_io (input offset voltage value) drift over the square root of the
calculated number of months (Equation 7).
Equation 7
V_io
=
------^V----ⁱ-^o---^d----^r--ⁱ--^f--^t-----
months
where V_io drift is the measured drift value in the specified test conditions after 1000 h stress
duration.
4.5
Schematic optimization aiming for low power
To benefit from the full performance of the The OA1NP, OA2NP and OA4NP series, the
impedances must be maximized so that current consumption is not lost where it is not
required.
For example, an aluminum electrolytic capacitance can have significantly high leakage. This
leakage may be greater than the current consumption of the op amp. For this reason,
ceramic type capacitors are preferred.
For the same reason, big resistor values should be used in the feedback loop. However,
there are three main limitations to be considered when choosing a resistor.
1. When the The OA1NP, OA2NP and OA4NP series is used with a sensor: the
resistance connected between the sensor and the input must remain much higher than
the impedance of the sensor itself.
2. Noise generated: a100 k resistor generates 40 ^{---n---V-----} , a bigger resistor value generates
Hz
even more noise.
3. Leakage on the PCB: leakage can be generated by moisture. This can be improved by
using a specific coating process on the PCB.
DocID025993 Rev 2
19/31
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