Amplifier design, especially for high-voltage applications, remains a complex challenge even for experienced analog engineers. Most commercial op amps are limited to power supplies of ±15V or lower, and with the trend toward smaller semiconductor geometries, many modern amplifiers operate at even lower voltages—like 5V or 3.6V. However, there is still a strong demand for circuits that can handle higher voltages. While discrete component solutions can be used to extend the operating range of lower voltage op amps, these approaches often introduce issues like mismatch, limited board space, and thermal challenges. The introduction of new high-precision monolithic op amps, such as the LTC6090, LTC2057, and LT6016, has made it much easier to design high-voltage analog systems.
The LTC6090 is a standout example, offering a supply voltage of up to ±70V without compromising the performance expected from a high-precision amplifier. It features a MOS input stage with an ultra-low input bias current of typically 3pA at 25°C, along with a low input offset voltage (less than 1.6mV) and a noise level of 11nV/√Hz at 10kHz. Its rail-to-rail output allows the device to drive signals up to 140VP-P, making it ideal for demanding high-voltage applications. Available in both 8-lead SOIC and 16-lead TSSOP packages, the LTC6090 includes a bare pad for improved thermal management, which helps maintain optimal performance under high load conditions.
In addition to its electrical performance, the LTC6090 also simplifies high-voltage design through its built-in thermal protection and easy integration with low-voltage control lines. This makes it a reliable choice for applications where stability and safety are critical.
One practical application of the LTC6090 is in transimpedance amplifier circuits, where it can significantly improve dynamic range. For instance, using a 125V supply rail allows for a high transimpedance gain of 1MΩ, which enhances signal-to-noise ratio. By attenuating the output, the system can maintain a clean signal within a 0–12V range, with noise levels as low as 21μVRMS in the 1kHz to 40kHz band.
In high-impedance applications like photodiodes, the LTC6090’s low input bias current is crucial. The device exhibits a logarithmic relationship between input bias current and temperature, doubling every 10°C but remaining very low even at 125°C. This makes it well-suited for precision measurements in varying environmental conditions.
Leakage currents can also be a concern in high-voltage designs, particularly when dealing with sensitive inputs. To mitigate this, special care must be taken during PCB layout. Using low-leakage materials and implementing a guard ring around the input nodes can help prevent unwanted leakage. The LTC6090’s TSSOP package includes eight protection pins that can be used to create a guard ring, enhancing reliability and accuracy.
Another important use case for high-voltage amplifiers is buffering DAC outputs. For example, the LTC6090 can be used to generate a 140VP-P signal from a 2.5V DAC, enabling precise control of high-voltage actuators, lasers, or piezoelectric devices.
Thermal management is also a key consideration. The LTC6090 consumes 378mW at 140V, and adding a load can push power consumption beyond 1W. To manage heat effectively, the package includes an exposed pad connected to the negative supply rail. Soldering this pad to a large copper area on the PCB improves thermal dissipation. With proper layout, the thermal resistance can be as low as 33°C/W, allowing the device to operate safely even under heavy loads.
The LTC6090 also includes multiple thermal protection features. An output disable (OD) function turns off the output stage when the junction temperature exceeds 145°C, preventing overheating. A second thermal shutdown activates at 175°C, ensuring long-term reliability. These features help protect the device from catastrophic failures while maintaining stable operation.
In conclusion, the LTC6090, along with other high-voltage op amps like the LTC2057 and LT6016, provides a powerful solution for high-voltage analog design. These devices offer exceptional performance, flexibility, and safety features, making them ideal for a wide range of applications—from precision measurement systems to high-voltage control circuits. Their ability to operate at extended voltages while maintaining low noise, high accuracy, and robust thermal management sets them apart in the world of analog electronics.
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