The EL8171 and EL8172 are micropower instrumentation amplifiers optimized for single-supply operation in the +2.4V to +5.5V range. Inputs and outputs can operate rail-to-rail. As with all instrumentation amplifiers, a pair of inputs provides very high common-mode rejection and is completely independent of a pair of feedback terminals. The feedback terminal allows zero input to translate to any output offset, including ground. The feedback divider controls the overall gain of the amplifier.

The EL8172 has a gain of 100 or higher and the EL8171 has a gain of 10 or higher. The EL8171 and EL8172 feature PMOS input devices that provide sub-nA input bias currents.

The amplifier can be powered by one Li-ion battery or two NiCd batteries. The EL8171 and EL8172 input ranges from below ground to slightly above the positive rail. The output stage swings fully to ground (ground sense) or positive supply - no pull-up or pull-down resistors required.

Product Description

The EL8171 and EL8172 are micropower instrumentation amplifiers (instrumentation amplifiers) that provide rail-to-rail input amplification with rail-to-rail output swings ranging from 2.4V to 5.5V. The EL8171 and EL8172 also offer excellent DC and AC specifications while consuming only 65µA of typical supply current. Because the EL8171 and EL8172 provide a pair of independent feedback terminals to set the gain and adjust the output level, these instrumentation amplifiers achieve a high common-mode rejection ratio regardless of the tolerance of the gain-setting resistors. The EL8171 is internally compensated for a minimum closed loop gain of 10 or higher, ideal for medium to high gains. For higher gain, the EL8172 compensates internally for a minimum gain of 100.

input protection

All input and feedback terminals of the EL8171 and EL8172 have internal ESD protection diodes, positive and negative supply rails, limiting the input voltage to within one diode drop beyond the supply rails. The inverting input and FB- input have ESD diodes connected to the V rail, and the non-inverting input and FB+ terminals have ESD diodes from the V+ rail. The EL8172 has additional back-to-back diodes on the input terminals that also span the feedback terminals. If overdriving the input is necessary, the external input current must not exceed 5mA. On the other hand, the EL8171 has no clamps to limit the voltage on the differential input terminals allowing higher differential input voltages in lower gain applications. However, it is recommended that the input terminals of the EL8171 not be overdriven by 1V to avoid offset drift. External protection with external series resistors can be used to limit excessive external voltages and currents that can damage the input.

Input Stage and Input Voltage Range

The input terminals (IN+ and IN-) of the EL8171 and EL8172 are input range enhancement circuits (IREC) assisted by a single differential pair P-MOSFET device to increase the operating margin of the common mode input voltage. The feedback terminals (FB+ and FB-) also have a similar topology. As a result, the input common-mode voltage ranges of the EL8171 and EL8172 are both rail-to-rail. These instrumentation amplifiers are capable of handling input voltages at or slightly above power and ground making these instrumentation amplifiers ideal for single 5V or 3.3V low voltage supply systems. It is not necessary to move the common-mode input of the in-amp to achieve symmetrical input voltages. Output Stage and Output Voltage Range A pair of complementary MOSFET devices drives the output VOUT to within a few mV of the supply rails. At a 100kΩ load, the PMOS sources current and pulls the output up to 4mV below the positive supply, while the NMOS sinks current and current pulls the output down to 4mV above the negative supply, or to ground in the case of single supply operation. Currently the absorbing and sourcing capabilities of the EL8171 and EL8172 are internally limited to less than 35mA.