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LMP8602-Q1: Maximum *differential* voltage input w/o damage to device?

Thomas Schmit9
Prodigy 70 points
Part Number: LMP8602-Q1
Other Parts Discussed in Thread: LMP8602

The datasheet states: "The LMP860x and LMP860x-Q1 use level shift resistors at the inputs. Because of these resistors, the LMP860x and LMP860x-Q1 can easily withstand very large differential input voltages that may exist in fault conditions where some other less protected high-performance current sense amplifiers might sustain permanent damage." 

What does "very large" mean?

I have an application where the current that needs to be accurately monitored is fairly small (mA) but can occasionally peak at 25 amps for a short duration (600 uS, using 10 mS as a design value). For the range of current monitoring I'm interested in, a current sense resistor on the order of 1 ohm would be appropriate. I have identified one that can handle the occasional (i.e. less than once per minute) power pulses without burning up. The part I'm concerned with is the LMP8602 amplifier. From a measurement perspective, I don't care that I'll rail the output at 5 amps, but I do care about survivability. Will the device be damaged or degraded by being subjected to a differential voltage of 24 or 30 volts?

  • 0
    TI__Expert 4915 points

    Hi Thomas,

    All of our automotive parts (Q1 Standard) are spec'd to a situation where the sense inputs may either become shorted to the rails or open without causing damage or change in the part spec's, however it is impossible to say whenever accommodating these as part of a final design will bring unknown issues down the line, regarding long term part survivability.

    Another long term consideration is whenever the sense resistor can actually cope with this. We've seen many cases where they simply change value over time before failing open, after a period of time being exposed to such transients.

    My recommendation is to place a diode in series with the sense resistor (or two, back to back, for a bi-directional current flow) so that, if current increases past a value at which the voltage developed across the 1 ohm resistor is higher than the diode forward voltage drop, the excess can flow trough the diode instead. It is relatively trivial to find a diode that can withstand short peaks at 25-30Amps and it will be a more robust design, less susceptible to unexpected issues in the future, while not compromising the performance of the device under normal operating conditions.