ZHCS020J January 2011 – March 2021 OPA2835 , OPA835
PRODUCTION DATA
The OPA835 device is tested in this application in a unity-gain buffer configuration. A buffer configuration is selected as the configuration maximizes the loop gain of the amplifier configuration. At higher closed-loop gains, the loop gain of the circuit reduces, which results in degraded harmonic distortion. The relationship between distortion and closed loop gain at a fixed input frequency can be seen in Figure 7-36 in Section 7.9. The test was performed under varying output-load conditions using a resistive load of 300 Ω and 100 KΩ. Figure 7-34 shows the distortion performance of the amplifier versus the output resistive load. Output loading, output swing, and closed-loop gain play a key role in determining the distortion performance of the amplifier.
The 100-pF capacitor to ground on the input helped to decouple noise pickup in the lab and improved noise performance.
The Audio Precision was configured as a single-ended output in this application circuit. In applications where a differential output is available, the OPA835 device can be configured as a differential to single-ended amplifier as shown in Figure 9-4. Power supply bypassing is critical to reject noise from the power supplies. A 2.2-μF power-supply decoupling capacitor must be placed within two inches of the device and can be shared with other op amps on the same board. A 0.1-μF decoupling capacitor must be placed as close to the power supply pins as possible, preferably within 0.1 inch. For split supply, a capacitor is required for both supplies. A 0.1-µF capacitor placed directly between the supplies is also beneficial for improving system noise performance. If the output load is heavy, from 16 Ω to 32 Ω, amplifier performance could begin to degrade. To drive such heavy loads, both channels of the OPA2835 device can be paralleled with the outputs isolated with 1-Ω resistors to reduce the loading effects.