Test & measurement


Precision ultra low power high-side current sense


voltage of just 5 µV and draws just 1.4 µA, making it a great choice for building a complete ultra low power, precision high-side current sense circuit, as shown in Figure 1. This circuit uses only 2.3 µA to 280 µA of supply current to sense


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currents over a wide 100 µA to 250 mA dynamic range. The exceptionally low offset of the LTC2063 allows this circuit to work with only 100 mΩ of shunt resistance, limiting the maximum shunt voltage to only 25 mV. This minimises power loss on the shunt resistor and maximises power available to the load. The LTC2063’s rail-to-rail input allows this circuit to operate with very small load current where input common mode is almost at the rail. The integrated EMI filter of the LTC2063 protects it from RF interference in noisy conditions. The voltage output of this circuit for a given sense current is:


recision high-side measurement of microamp currents requires a small value sense resistor and a low offset voltage amplifier. The LTC2063 zero-drift amplifier has a maximum input offset


In this article, Catherine Chang, applications engineer in the Linear Products and Solutions Group at Analog Devices, discusses ADI’s LTC2063 zero-drift amplifier


Zero PoInT A critical specification for a current sense solution is the zero point, or equivalent error current, at the input for the output produced when no sense current is present. The zero point is generally determined by the


input offset voltage of the amplifier divided by RSENSE. The LTC2063’s low input offset voltage of typical 1 µV, maximum 5 µV, and low typical input bias and offset currents of 1 pA to 3 pA, allow for a zero point input-referred error current of only 10 µA (1 µV/0.1 Ω) typically, or 50 µA (5 µV/0.1 Ω) maximum. This low error allows the sense circuit to maintain its linearity down to the lowest current in its specified range (100 µA), without plateauing due to loss of resolution, as seen in Figure 2. The resulting input current to output voltage plot is linear over the entire current sense range.


Figure 1. Precision high-side current sense circuit based on the LTC2063 zero-drift amplifier.


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August 2020 Instrumentation Monthly


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