Datasheet LT6010 (Analog Devices) - 10

LT6010
U U W U APPLICATIO S I FOR ATIO Preserving Input Precision
allowed) for a 10V differential input voltage. Use additional external series resistors to limit the input current to 10mA Preserving the input accuracy of the LT6010 requires that in applications where differential inputs of more than 10V the applications circuit and PC board layout do not intro- are expected. For example, a 1k resistor in series with each duce errors comparable to or greater than the 20µV typical input provides protection against 30V differential voltage. offset of the amplifier. Temperature differentials across the input connections can generate thermocouple volt-
Input Common Mode Range
ages of 10’s of microvolts, so the connections to the input leads should be short, close together, and away from heat The LT6010 output is able to swing nearly to each power dissipating components. Air currents across the board supply rail (rail-to-rail out), but the input stage is limited to can also generate temperature differentials. operating between V– + 1V and V+ – 1.2V. Exceeding this common mode range will cause the gain to drop to zero, The extremely low input bias currents (20pA typical) allow however no phase reversal will occur. high accuracy to be maintained with high impedance sources and feedback resistors. The LT6010 low input
Total Input Noise
bias currents are obtained by a cancellation circuit on- chip. The input bias currents are permanently trimmed at The LT6010 amplifier contributes negligible noise to the wafer testing to a low level. Do not try to balance the input system when driven by sensors (sources) with impedance resistances in each input lead; instead, keep the resistance between 20kΩ and 1MΩ. Throughout this range, total at either input as low as possible for maximum accuracy. input noise is dominated by the 4kTRS noise of the source. If the source impedance is less than 20kΩ, the input Leakage currents on the PC board can be higher than the voltage noise of the amplifier starts to contribute with a LT6010’s input bias current. For example, 10GΩ of leak- minimum noise of 14nV/√Hz for very low source imped- age between a 15V supply lead and an input lead will gen- ance. If the source impedance is more than 1MΩ, the input erate 1.5nA! Surround the input leads by a guard ring, driven current noise of the amplifier, multiplied by this high to the same potential as the input common mode, to avoid impedance, starts to contribute and eventually dominate. excessive leakage in high impedance applications. Total input noise spectral density can be calculated as:
Input Protection
v = e 2 + kTR 4 + i( R 2 n(TOTAL) n S n S) The LT6010 features on-chip back-to-back diodes be- tween the input devices, along with 500Ω resistors in where en = 14nV/√Hz, in = 0.1pA/√Hz and RS the total series with either input. This internal protection limits the impedance at the input, including the source impedance. input current to approximately 10mA (the maximum sn6010 6010fs 10