Quad CMOS op-amp for low-power signal chains
The Texas Instruments OPA4345UA is a quad-channel CMOS operational amplifier from the MicroAmplifier™ series, with four rail-to-rail output amplifiers in a 14-SOIC package. It has a 3 MHz gain-bandwidth product and 2V/µs slew rate, and draws 150 µA total supply current.
150 µA supply — the power budget decider
The headline number for this part is the 150 µA supply current across all four amplifiers. In a three-wire 4-20 mA transmitter, the total electronics budget is typically 3.5 mA to leave headroom for the sensor and loop. Four OPA4345UA channels consume 0.15 mA of that — leaving the rest for the sensor excitation, reference, and microcontroller. The 0.2 pA CMOS input bias current means the amplifier does not load high-impedance sources like pH probes or photodiode transimpedance stages, preserving the signal integrity without a separate buffer.
Rail-to-rail output swing lets each channel drive an ADC input or a comparator threshold without losing headroom at the rails. The 15 mA per-channel output current is enough to drive a reference input or a modest cable capacitance, though not intended for heavy loads like solenoids or relays.