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Part Number: TLV369
Hope you are doing well. See below customer question;
I am using this part as a buffer in my circuit. It appears the part has a very high leakage at the positive input even though the spec sheet says it has a very high input impedance and very low leakage current. I have attached a snippet of my schematic below. Please note R107 & R108 in my schematic are NOT loaded. I am charging a capacitor (100nF film capacitor) which is connected to the positive input of the op amp as a reference voltage. The negative input is connect to the output for a gain = 1. The voltage source charging the capacitor is then removed and I expect the capacitor to stay charged for a relatively long time (20mV drop > 200 seconds). However, it is discharging very fast. Can someone please explain why this is happening? I selected this part to be low power with a very high input impedance.
Randhir S Kalsi
Technical Sales Engineer
There are a few possibilities for why the leakage here may be higher than expected. Firstly, while the TLV369's input bias current is 10pA typical, the leakage current of the ISL43120IHZ will also contribute. Given that this current can be up to 10x larger than the TLV369's bias current, this could be a possible contributing factor.
Another possibility is flux or other contamination on the PCB. We have seen cases where flux contamination on the PCB contributed microamps of leakage to otherwise low-leakage circuits. Keep in mind that this is possible even with so-called "no-clean" flux. If the PCB was assembled with water-soluble flux, a wash with deionized water in an ultrasonic bath should remove much of the flux contamination.
For rosin-core or other soldering fluxes, a more aggressive solvent may be required to remove the flux residue - if in doubt, consult the solder manufacturer's recommended cleaning instructions.
For more information on flux contamination, see this article by Ian Williams.
Precision Amplifier Applications - TI Tucson
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In reply to Alexander Davis:
Thanks Alex. As always, TI Tucson team providing top notch support!
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