Datasheet LT1468-2 (Analog Devices) - 9

LT1468-2
applicaTions inForMaTion Input Considerations
The input bias currents vary with common mode voltage Each input of the LT1468-2 is protected with a 100Ω as shown in the Typical Performance Characteristics. The series resistor and back-to-back diodes across the bases cancellation circuitry was not designed to track this com- of the input devices. If the inputs can be pulled apart, the mon mode voltage because the settling time would have input current should be limited to less than 10mA with been adversely affected. an external series resistor. Each input also has two ESD The LT1468 inputs can be driven to the negative supply clamp diodes—one to each supply. If an input is driven and to within 0.5V of the positive supply without phase above the supply, limit the current with an external resistor reversal. As the input moves closer than 0.5V to the posi- to less than 10mA. tive supply, the output reverses phase. The LT1468-2 employs bias current cancellation at the
Total Input Noise
inputs. The inverting input current is trimmed at zero common mode voltage to minimize errors in inverting The curve of Total Noise vs Unmatched Source Resistance applications such as I-to-V converters. The noninverting in the Typical Performance Characteristics shows that input current is not trimmed and has a wider variation with source resistance below 1k, the voltage noise of the and therefore a larger maximum value. As the input offset amplifier dominates. In the 1k to 20k region the increase in current can be greater than either input current, the use noise is due to the source resistance. Above 20k the input of balanced source resistance is NOT recommended as it current noise component is larger than the resistor noise. actually degrades DC accuracy and also increases noise.
Input Stage Protection
R1 R2 100Ω 100Ω Q1 Q2 +IN –IN 14682 AI03 14682fb 9 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Applications Information Simplified Schematic Package Description Revision History Typical Application Related Parts