Part Number: OPA320
My customers are looking for operational amplifiers with extremely low temperature drift input bias current fluctuation at Ta -10°C to 70°C.
Required specifications: max 10 pA @ 70°C
OPA320 is max 50pA at -40°C to 85°C , but it seems that there is no temperature drift up to 70°C in Figure 10. Input Bias Current vs Temperature in the data sheet.
I will ask for the following.
・ Figure 10. Expanding vertical axis of Input Bias Current vs Temperature.(Same as OPA 340 data sheet Figure 13.)
・ Input Bias Current Max. Value (Ta = -10°C to 70°C)
Required specifications: max 10 pA @ 70°C. OPA320 is max 50pA at -40°C to 85°C , but it seems that there is no temperature drift up to 70°C in Figure 10. Input Bias Current vs Temperature in the data sheet.
The OPA320 is a CMOS input operational amplifier. The input bias current is dominated by the leakage current associated with the reverse-biased input ESD current steering diodes connected from the inputs, to the internal supply rails. Thus, Figure 10, the Input Bias Current vs Temperature curve is that of the reverse-biased diode leakage observed across temperature. It is a typical diode curve where the leakage current approximately doubles for every 10°C increase in temperature. The curve assures that the leakage will always be higher at 85°C, than it is at 70°C.
・ Figure 10. Expanding vertical axis of Input Bias Current vs Temperature.(Same as OPA340 data sheet Figure 13.)
OPA320 Figure 10 has a linear vertical scale with a maximum of 1300 pA (150 C max), compared to the OPA340 Figure 13 which has a logarithmic vertical scale with a maximum of 1000 pA (125°C). I agree that the log scale provides finer resolution in the portion of the diode curve where the current begins to quickly change. Keep in mind that these are "typical" curves and the input bias current levels will be different for each device.
The Electrical Characteristics table states that the maximum input bias current over the temperature, range TA = –40°C to 85°C, is ±50 pA. Therefore, since the TA = -10°C to 70°C temperature falls within that wider range the maximum is the same ±50 pA.
I will check and see if there is another op amp that has an Ib specification that assures a maximum of +/-10 pA, over TA = -10°C to 70°C. Are there any other critical parameters?
Precision Amplifiers Applications Engineering
In reply to Thomas Kuehl:
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