13

OPA855

www.ti.com

SBOS622 – JULY 2018

Product Folder Links: OPA855

Submit Documentation Feedback

Copyright © 2018, Texas Instruments Incorporated

9.4 Device Functional Modes

9.4.1 Split-Supply and Single-Supply Operation

The OPA855 can be configured with single-sided supplies or split-supplies. Split-supply operation using balanced

supplies with the input common-mode set to ground eases lab testing because most signal generators, network

analyzers, spectrum analyzers, and other lab equipment typically reference inputs and outputs to ground. Split-

supply operation is preferred in systems where the signals swing around ground. However, the system requires

two supply rails. In split-supply operation, the thermal pad must be connected to the negative supply.

Newer systems use a single power supply to improve efficiency and reduce the cost of the extra power supply.

The OPA855 can be used with a single positive supply (negative supply at ground) with no change in

performance if the input common-mode and output swing are biased within the linear operation of the device. To

change the circuit from a split-supply to a single-supply configuration, level shift all the voltages by half the

difference between the power supply rails. In this case, the thermal pad must be connected to ground.

9.4.2 Power-Down Mode

The OPA855 features a power-down mode to reduce the quiescent current, which conserves power. Driving the

PD pin LOW (less than 0.8 V) disables the amplifier, consuming a standby current of less than 200 µA. Raise the

PD pin HIGH (greater than 1.2 V) to enable the amplifier.

The PD disable and enable threshold voltages are with reference to the negative supply. If the amplifier is

configured with the positive supply at 3.3 V and the negative supply at ground, then the disable and enable

threshold voltages are 0.8 V and 1.2 V, respectively. If the amplifier is configured with ±2.5-V supplies, then the

threshold voltages are at –1.7 V and –1.3 V, respectively.

Connecting the PD pin low disables the amplifier and places the output in a high-impedance state. When the

parallel load to the output of the amplifier. To protect the input stage of the amplifier, the OPA855 uses internal,

back-to-back protection diodes between the inverting and noninverting input pins as Figure 6 shows. When the

differential voltage between the input pins of the amplifier exceeds a diode voltage drop, an additional low-

impedance path is created between the inputs.