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TLV3605: Input differential mode resistance range

Ben Campbell
Prodigy 70 points
Part Number: TLV3605

Tool/software:

Dear E2E,

I am using this comparator in an application where a signal is fed to the positive comparator input and a reference signal is fed to the negative comparator input. The reference signal is generated by a voltage-output DAC. To minimise the cost of the DAC, I'm using a 8-bit DAC, with a voltage divider scaling-down the DAC output voltage into a range of about 0V to 0.1V. This voltage divider effectively increases the system's reference voltage resolution to that of a 12-bit DAC without voltage divider. 

I am trying to work out what values to use for the resistors in the voltage divider. In the TLV3605 datasheet, the input-differential-mode resistance Rdm is specified as typically 67k. This resistance will be in parallel with the bottom resistor of the potential divider. But the Rdm spec has no min/max, only typical. 

Please could you advise what are the min/max range of the Rdm?

Many thanks,

Ben

  • +1
    Guru 304470 points

    I suspect that that low RDM value describes the discontinuity that happens about 1.3 V below VCC. (The slope is roughly 0.1 V / 2 µA = 50 kΩ.)

    How often does the reference signal change? I'd guess that you need to care only about the DC characteristics, i.e., input bias current of at most 5 µA.

  • 0 in reply to Clemens Ladisch
    Prodigy 70 points

    Thanks Clemens. Thanks for highlighting the input bias plots and spec, which does have min/max defined. I think I'll choose the resistors with sufficient current that the maximum 5µA bias current is negligible.