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RE: ADS1018-Q1: Input Leakage Current on analog input pins

user5250576
Prodigy 40 points
Other Parts Discussed in Thread: ADS1120, ADS1018, ADS1118

Hi Joseph,

I also interested in the input leakage current. But that current is caused by the protection diodes (shown in Figure 8 in datasheet) instead of the capacitors! I have already found a typical value in sbaa355 application note:

"Based on the typical characteristics curves, the absolute input current is 250nA depending upon temperature, input voltage, and input channel."

We want to use this ADC in our new product that will working in wide temperature range  (-40°C..+85°C) with relative large resistors on the inputs. On large resistors the input bias current could be caused significant error, so this parameter is important. Could you provide a more specific characteristic about the bias current? It would be very helpful for us.

Thank you for your help in advance!

Peter

  • 0
    TI__Guru* 92715 points

    Peter,

    I'm going to split this into it's own post.

    First, I wanted to point out that the application note that you referenced (SBAA355) refers to the ADS1120 instead of the ADS1018. If you want an application note more aligned to the ADS1018, the (SBAA354) uses the ADS1118 which is the 16-bit version of the ADS1018.

    As I mentioned earlier, SBAA355 references the ADS1120, which does give specific input current details in the typical characteristics curves in the datasheet. If you look at those curves, you can see the absolute and differential input currents. I think I just took the largest current seen on Figure 18. I would note that this is a rather extreme point, with the input near the positive supply and at 125C.

    Again, the ADS1018 is a different device. I don't have any specific data on the input leakage of the device. However, 85C is a rather low temperature to have significant leakage. Diodes will generally have an exponential rise in current with high temperature. Even if you look in the ADS1120 curves, the 85C are still small in comparison to the 125C curves.

    Joseph Wu