35

OPA810

www.ti.com

SBOS799A – AUGUST 2019 – REVISED DECEMBER 2019

Product Folder Links: OPA810

Submit Documentation Feedback

Copyright © 2019, Texas Instruments Incorporated

Layout Guidelines (continued)

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 OPA810 is 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 134.8°C/W for the SOIC package, and an internal power of 24-V

supply × 4.7-mA 125°C supply current gives a maximum internal power dissipation of 113 mW. This power

gives a 15°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 device such as the OPA810 is not recommended. The additional lead length

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

that can almost make achieving a smooth, stable frequency response impossible. Best results are obtained

by soldering the OPA810 onto the board.

11.1.1 Thermal Considerations

The OPA810 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.

buffer, operating on ±12-V supplies at an ambient temperature of 25°C and driving a grounded 500-Ω load.