SNOS760C May 1999 – September 2014 LM7171
Bypassing the power supply is necessary to maintain low power supply impedance across frequency. Both positive and negative power supplies should be bypassed individually by placing 0.01 μF ceramic capacitors directly to power supply pins and 2.2 μF tantalum capacitors close to the power supply pins.
To minimize reflection, coaxial cable with matching characteristic impedance to the signal source should be used. The other end of the cable should be terminated with the same value terminator or resistor. For the commonly used cables, RG59 has 75Ω characteristic impedance, and RG58 has 50Ω characteristic impedance.
Amplifiers driving capacitive loads can oscillate or have ringing at the output. To eliminate oscillation or reduce ringing, an isolation resistor can be placed as shown in Figure 62. The combination of the isolation resistor and the load capacitor forms a pole to increase stability by adding more phase margin to the overall system. The desired performance depends on the value of the isolation resistor; the bigger the isolation resistor, the more damped the pulse response becomes. For LM7171, a 50Ω isolation resistor is recommended for initial evaluation. Figure 63 shows the LM7171 driving a 150 pF load with the 50Ω isolation resistor.
The maximum power allowed to dissipate in a device is defined as:
For example, for the LM7171 in a SOIC-8 package, the maximum power dissipation at 25°C ambient temperature is 730 mW.
Thermal resistance, R θJA, depends on parameters such as die size, package size and package material. The smaller the die size and package, the higher RθJA becomes. The 8-pin DIP package has a lower thermal resistance (108°C/W) than that of 8-pin SOIC (172°C/W). Therefore, for higher dissipation capability, use an 8-pin DIP package.
The total power dissipated in a device can be calculated as:
For example, the total power dissipated by the LM7171 with VS = ±15V and output voltage of 10V into 1 kΩ is