OPA2132: the maximum input current of the OPA2132UA

Hello DDoor,

The OPA2132UA datasheet Electrical Characteristics table 6.4 lists the Input Bias Current as 5 pA typical, and ±50 pA maximum with VCM = 0 V and Note (2) High-speed test at TJ = 25°C. However, if the OPA2132 is operating in a continuous power mode it will continuously dissipate power and the input JFETs will self heat to a temperature higher than 25°C resulting in increased input bias current.

Datasheet Figure 5. "Input Bias Current vs Temperature" provides a set of typical curves for the different OPA132 and OPA2132 package types. You can see from the curves that the typical OPA2132UA (Dual curve) is about 20 pA at an Ambient Temperature of 25°C. The curves account for the self heating of the input JFETs that occurs when continuously powered.

A maximum input bias current is not specified for any condition beyond what is listed in the datasheet; specifically, the Note (2) high speed test at TJ = 25°C. But based on the Figure 5. curves, the OPA2132UA typical power dissipation, and the ±50 pA maximum under the Note (2) conditions, a realistic estimation of the maximum input bias current is about ±400 pA with a TA = 25°C. Likely, the input bias current will be less than this estimated maximum. Note that TI does not make any assurances of the estimated maximum because it is not stated in the data sheet.

A common issue with changing op amp input bias current is directly related to PC board cleanliness. If the PC board has any residual solder flux or other contamination between the op amp pins, or bridging the pins from underneath the device, leakage current paths which affect the input bias current levels may be present. The flux contamination results in unintended, unreliable resistors that can change with temperature and humidity over time.

We use solder having water soluble flux on our PC boards. They are ultrasonically cleaned twice using clean DI water. This is effective in removing any residual flux on the PC board, and on and under the op amp packages and their pins. The boards a dried in a oven to help dry out any residual moisture associated with the cleaning process. A clean PC board should allow for the low input bias current levels associated with JFET input op amps. They should remain low and stable over time.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hello,
Thomas

Thank you for your response.

Although my explanation was bad,
The absolute maximum rating of this device is
Input voltage (V -) - 0.7 (V +) + 0.7,
I think that this 0.7 V is a clamp diode,
How many milliamps A can flow to this 0.7 V VF?
(How much is IF?)

Best regards,
DDdoor

Hello DDdoor,

The diode connected from each OPA2132 input, to each internal power supply rail are used to protect the device from out of circuit ESD events. They clamp the inputs to the supply rails in such instances.The ESD diodes are specially designed to have very low leakage current so that they don't degrade the input bias current of the operational amplifier in normal operation. They will turn on if the input voltage is raised to a level beyond the supply rail where they become forward biased.

The OPA2132 ESD diodes conduct with a forward current level of about 250 uA, with the maximum specified applied 0.7 V across them. That is completely safe current level for the diodes which can typically handle 10 mA without any damage.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hello,
Dennis

I am grateful for your answer.

Your answer was what I wanted to hear.
For this reason, I informed the customer about the contents.

Best regards,
DDdoor