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OPA2863

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SBOS982A – JUNE 2020 – REVISED JUNE 2020

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Copyright © 2020, Texas Instruments Incorporated

Layout Guidelines (continued)

trace is required, and the 6-dB signal loss intrinsic to a doubly-terminated transmission line is acceptable,

implement a matched impedance transmission line using microstrip or stripline techniques (consult an ECL

design handbook for microstrip and stripline layout techniques). A 50-Ω environment is normally not

necessary onboard, and a higher impedance environment improves distortion. With a characteristic board

trace impedance defined based on board material and trace dimensions, a matching series resistor into the

trace from the output of the OPAx863 devices are used as well as a terminating shunt resistor at the input of

the destination device. Remember also that the terminating impedance is the parallel combination of the

shunt resistor and the input impedance of the destination device— this total effective impedance must be set

to match the trace impedance. If the 6-dB attenuation of a doubly-terminated transmission line is

unacceptable, a long trace can be series-terminated at the source end only. Treat the trace as a capacitive

load in this case and set the series resistor value to obtain sufficient phase margin and stability. This does

not preserve signal integrity as well as a doubly-terminated line. If the input impedance of the destination

device is low, the signal attenuates because of the voltage divider formed by the series output into the

terminating impedance.

5. Take care to design the PCB layout for optimal thermal dissipation. For the extreme case of 125°C

operating ambient, using the approximate maximum 180.3°C/W for the DGK package, and an internal power

of 12-V supply × 2.6-mA 125°C supply current (both amplifiers together) gives a maximum internal power

dissipation of 31.2 mW. This power gives a 5.6°C increase from ambient to junction temperature. Load

power adds to this value and this dissipation must also be calculated to determine the worst-case safe

operating point.

6. Socketing a high speed part like the OPAx863 devices are not recommended. The additional lead

length and pin-to-pin capacitance introduced by the socket can create an extremely troublesome parasitic

network which can make it almost impossible to achieve a smooth, stable frequency response. Best results

are obtained by soldering the OPAx863 devices onto the board.

11.1.1 Thermal Considerations

The OPA2863 does not require heat sinking or airflow in most applications. Maximum allowed junction

temperature sets the maximum allowed internal power dissipation. Do not allow the maximum junction

temperature to exceed 150°C.

depends on the required output signal and load but would, for a grounded resistive load, be at a maximum when

the output is fixed at a voltage equal to half of either supply voltage (for equal split-supplies). Under this condition

The power in the output stage and not into the load that determines internal power dissipation.

unity gain buffer, operating on ±6-V supplies at an ambient temperature of 25°C and driving a grounded 500-Ω

load.