OPA656 is a broadband, unity gain stable, field-effect transistor input operational amplifier 12

thermal analysis

OPA656 does not require heat dissipation or airflow in most applications. The maximum allowed junction temperature will set the maximum allowed internal power consumption, as described below. In any case, the maximum connection temperature shall not exceed 150 ° C.diode

The working junction temperature (TJ) is given by TA+PD •θ JA. The total internal power consumption (PD) is the sum of the static power (PDQ) and the additional power consumed in the output stage (PDL) to provide load power. Static power supply is simply the product of the specified no-load power supply current and the total power supply voltage of the entire component. PDL will depend on the required output signal and load, but for ground resistance loads, PDL will be at its maximum value when the output is fixed at a voltage equal to half of any power supply voltage (for equal bipolar power supplies). Under these conditions, PDL=VS2/（4•RL）， RL includes feedback network loading.diode

Note that it is the output stage power, not the load, that determines the internal power consumption.

As the worst example, calculate the maximum TJ using OPA65N (SOT3-5 package) in the circuit shown in Figure 1, which operates at a maximum specified ambient temperature of+85 ° C and drives a grounded 100 Ω load.diode 

PD=10V•16.1mA+52/（4•（100Ω| 800Ω））=231mW

The maximum TJ is+85 ° C+(0.23W • 150 ° C/W)=120 ° C.

All practical applications will operate at lower internal power and junction temperatures.

Board layout

To achieve optimal performance, using high-frequency amplifiers like OPA656 requires careful attention to board layout parasitic and external component types. Suggestions for optimizing performance include:diode

a) Minimize parasitic capacitance to any AC ground of all signal I/O pins. The parasitic capacitance on the output and inverter input pins can cause non rotational input instability, which reacts with the source impedance and causes unintentional band limitation. To reduce unnecessary capacitance, windows around the signal I/O pins should be opened on all ground and power planes. Otherwise, the ground and powered aircraft should remain uninterrupted in other parts of the ship.diode