DESCRIPTION

The LTC6090/LTC6090-5 are high voltage, precision monolithic operational amplifiers. The LTC6090 is unity gain stable. The LTC6090-5 is stable in noise gain configurations of 5 or greater. Both amplifiers feature high open loop gain, low input referred offset voltage and noise, and pA input bias current and are ideal for high voltage, high impedance buffering and/or high gain configurations.

The amplifiers are internally protected against overtemperature conditions. A thermal warning output, TFLAG, goes active when the die temperature approaches 150°C.  The output stage may be turned off with the output disable pin OD. By tying the OD pin to the thermal warning output (TFLAG), the part will disable the output stage when it is out of the safe operating area. These pins easily interface to any logic family.

Both amplifiers may be run from a single 140V or spit ±70V power supplies and are capable of driving up to 200pF of load capacitance. They are available in either an 8-lead SO or 16-lead TSSOP package with exposed pad for low thermal resistance.

 

FEATURES

Supply Range: ±4.75V to ±70V (140V)

0.1Hz to 10Hz Noise: 3.5μVP-P

Input Bias Current: 50pA Maximum

Low Offset Voltage: 1.25mV Maximum

Low Offset Drift: ±5µV/°C Maximum

CMRR: 130dB Minimum

Rail-to-Rail Output Stage

Output Sink and Source: 50mA

12MHz Gain Bandwidth Product

21V/µs Slew Rate

11nV/√Hz Noise Density

Thermal Shutdown

Available in Thermally Enhanced SOIC-8E or TSSOP-16E Packages

 

APPLICATIONS

ATE

Piezo Drivers

Photodiode Amplifier

High Voltage Regulators

Optical Networking

 

APPLICATIONS INFORMATION

General

The LTC6090 high voltage operational amplifier is designed in a Linear Technology proprietary process enabling a railto-rail output stage with a 140V supply while maintaining precision, low offset, and low noise.

Power Supply

The LTC6090 works off single or split supplies. Split supplies can be balanced or unbalanced. For example, two ±70V supplies can be used, or a 100V and –40V supply can be used. For single supply applications place a high quality surface mount ceramic 0.1µF bypass capacitor between the supply pins close to the part. For dual supply applications use two high quality surface mount ceramic capacitors between V+ to ground, and V– to ground located close to the part. When using split supplies, supply sequencing does not cause problems.

Input Protection

The LTC6090 has a comprehensive protection network to prevent damage to the input devices. The current limiting resistors and back to back diodes are to keep the inputs from being driven apart. The voltage-current relationship combines exponential and resistive until the voltage difference between the pins reach 12V.

Feedback Resistor Selection

To get the most accuracy, the feedback resistor should be chosen carefully. Consider an amplifier with AV = –50 and a 5k feedback resistor. A 1V input will cause the output to rise to 50V, causing 10mA to flow through the feedback resistor. The power dissipated in the output stage will create thermal feedback to the input stage potentially causing shifts in offset voltage. A better choice is a 50k feedback resistor reducing the current in the feedback resistor to 1mA.

Board Layout

The LTC6090 is a precision low offset high gain amplifier that requires good analog PCB layout techniques to maintain high performance. Start with a ground plane that is star connected. Pull back the ground plane from any high voltage vias. Critical signals such as the inputs should have short and narrow PCB traces to reduce stray capacitance which also improves stability. Use high quality surface mount ceramic capacitors to bypass the supply(s).

In addition to the typical layout issues encountered with a precision operational amplifier, there are the issues of high voltage and high power. Important consideration for high voltage traces are spacing, humidity and dust. High voltage electric fields between adjacent conductors attract dust. Moisture is absorbed by the dust and can contribute to board leakage and electrical breakdown.