Adding a header and jumper at J5 allows for simple disabling of the LMH5485-SP. An SMA connector can also be loaded at J4 to allow for a power-down signal to be applied for high-speed testing. Normally the J5 jumper is used to enable or disable (power-down) the amplifier. When jumper J5 is open, the amplifier is not powered down, so it is enabled. When the shorting block is connected and J5 is closed, the amplifier is powered down.

For high-speed testing, a 0-Ω resistor can be placed at C4 and a 50-Ω resistor at R6 to terminate the PD SMA input. The shorting block should be removed from J5 during high-speed testing. This is because 0-Ω at C4 terminates to the ground and not to the supplies. The state of the amplifier will be undefined when the signal source is disconnected. For this reason, 0-Ω at C4 should only be used when driving the SMA connector with a high speed, controlled impedance source.