Precision low-power op-amp works with up to 70V on its inputs

Precision low-power op-amp works with up to 70V on its inputs

Called ADA4098-1, its rail-to-rail input shows a strong Linear Tech legacy, and even carries ‘Over-the-top’ branding.

The amplifier, it can run from anywhere from +3V to +50V (or ±25V) (typical consumption 165μA) then, independent of supply rail voltage, the common-mode input range extends from 100mV below its negative power terminal, to 70V above that terminal.

Below this, the amplifier will survive if the inputs are pulled 10V below that negative terminal – due to 880Ω series resistors (see diagram).

“The inputs can tolerate up to 80V of differential voltage without damage or degradation to dc accuracy,” added the company.

Key to the voltage-tolerant inputs are a pair of pnp input stages (see diagram).

The Q1 and Q2 common emitter differential pair operates with inputs between the negative power terminal and 1.25V below the positive supply.

From there upwards the Q3 to Q6 common base input stage takes over – Q9 is on in this region, diverting bias current away from Q1 – Q2 to the M3 – M4 mirror, where M4 biases Q3 to Q6.

CMRR and PSRR are 123dB min (-100mV to +70V common mode) and 123dB min across +3 to ±25V supplies respectively.

The precision claim is associated with the ±30μV maximum input offset voltage and max drift is ±0.5μV/°C (for B grade) – with caveats.

Input offset current is ±700pA max with the inputs between the rails, but climbs to a higher figure (below 10μA) once they get near to and above the positive rail.

Related to the low current consumption, typical gain-bandwidth product is 1.05MHz and slew rate is 800mV/μs.

ADA4098-1 is unity-gain stable and can drive loads up to 20mA and 200pF.

Noise typically has a 6Hz 1/f corner, is 400nVp-p (0.1 – 10Hz) and 17nV/√Hz at 100Hz.

A shut-down pin is provided, and another useful form of shutdown can be achieved by disconnecting the positive supply terminal.

Packaging is 6pin TSOT.

The ADA4098-1 product page is here, and there is an evaluation board