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TMUX1511: Leakage current specs

Part Number: TMUX1511
Other Parts Discussed in Thread: TLV6741, TMUX1111

Hello,

I would like to use the TMUX1511 in an application as discussed in section 9.2.2 (Transimpedance Amplifier Feedback Control) of the data sheet. In section 9.2.2.2, the statement is made: "The TMUX1511 has a typical On-leakage current of less than 10 pA...". However, if one of the four switches is on, and the other three switches are off, then the off-leakage current is added to the photodiode current which is a source of error. Figure 10 plots the off-leakage current as a function of temperature, and is about 300pA at about 60C. The on-leakage current plot (Figure 8) shows about 10pA at about 60C, corresponding to the text mentioned above. So now we have three off switches at 300pA each, or 900pA for the sum. It seems that the off-leakage then overwhelms the low 10pA on-leakage, although it is still small enough compared to the 10uA example and still meets the 1% accuracy. So my question is, shouldn't the calculation be based on the off-leakage current since this is the dominant error source?

My second question is about the leakage specs in the 6.5 Electrical Characteristics section. Both the on and off-leakage current specs have very high maximum and minimum values, 50nA and 100nA, compared to the typical values, 10pA and 30pA. Looking at Figure 10 again, the off-leakage varies between 0nA and 0.8nA over temperature. But the spec in section 6.5 is from -100nA to +100nA. If I am to design a circuit with the four switches and a non-switched feedback resistor, then I would need to consider -400nA to +400nA as the maximum leakage currents (over temperature) contributing to the circuit error.My question is, then, are 50nA and 100nA the actual maximums to design to?

By the way, there is an excellent discussion of "Typical Specifications and Distributions" in section 8.3.6 of the TLV6741 op amp data sheet. From that discussion, I would take the typical spec of 10pA or 30pA for the leakage current as the one-sigma + mean value (most likely at 25C). I realize that the leakage current has a strong temperature dependence, but the plotted vs specified values don't seem to make sense.

Any comments or explanations are welcome.

Thank you, 

Scott

  • Hi Scott,

    Thanks for your thoughtful question and the reference to the op amp datasheet.

    1. The statement you are referring to in section 9.2.2.2 mentions the on-leakage current as a consideration in signal accuracy. Off-leakage current is a dominant source in the measurement. This example in the datasheet was left open-ended, as there are multiple combinations of number of switches in the on or off state. You can use the plots to calculate the estimated error for your function (as you have done at 60C), which as you mentioned, should meet the 1% accuracy.
    1. The typical characteristics plots show the typical value trends across voltage and temperatures, while the specification maximum and minimum values also account for process variations. The maximums you choose to design to are dependent on your system application accuracy needs. Many customers design towards typical parameters depending on the system accuracy requirements.

    I would also like to recommend taking a look at TMUX1111. TMUX1111 is a precision switch with considerably lower leakage current specifications (even at 60C). Let me know what you think about TMUX1111!

    Best regards,
    Kate