Performance and application of monolithic operational amplifiers

Photocoupler

Monolithic operational amplifiers have been around since the 1960s, but modern versions continue to evolve with improved performance. The LTC6090 is a high-precision monolithic op amp that pushes the boundaries by supporting supply voltages up to ±70V without compromising on other key features expected from precision devices. Available in both an 8-lead SO and a 16-lead TSSOP package, it includes exposed pads for better thermal management, reducing the need for external heat sinks. Its simple interface with low-voltage control lines and built-in thermal protection make it ideal for complex high-voltage analog designs.

High voltage and high performance go hand in hand when it comes to op amps. Key specifications like low input bias current, minimal offset voltage, and low noise are essential. The LTC6090 delivers on all fronts. It uses a MOS input stage with typically 3pA of input bias current at 25°C and less than 100pA at 85°C, making it perfect for high-impedance applications such as photodiode amplifiers. The device also offers a low input offset voltage of under 1.6mV and a noise level of just 11nV/√Hz at 10kHz. Its common-mode range extends to either 3V or 134V relative to either rail, even across a 140V supply.

Figure 1: Extended Dynamic Range 1M Transimpedance Photodiode Amplifier

On the output side, high-precision op amps must maintain accuracy when driving various loads. The LTC6090 excels here too. With a 10MHz gain-bandwidth product, high slew rate, and a rail-to-rail output stage capable of delivering ±10mA, it can handle capacitive loads up to 200pF. The example shown in Figure 2 demonstrates its ability to drive a 140VP-P 10kHz sine wave. As seen in Figure 3, the output swing remains stable even with increased load current. Additionally, the output voltage fidelity is maintained at 100VP-P up to 8kHz, as illustrated in Figure 4.

Figure 2: LTC6090 output voltage 140VP-P 10kHz sine wave

Figure 3: LTC6090 output voltage swing vs. load current

Figure 4: LTC6090 Total Harmonic Distortion + Noise Sum vs. Frequency