SLOS358C September 2011 – April 2020 THS4531
The THS4531 is designed for a nominal capacitive load of 2 pF (differentially). When driving capacitive loads greater than this, it is recommended to use small resisters (RO) in series with the output as close to the device as possible. Without RO, capacitance on the output will interact with the output impedance of the amplifier causing phase shift in the loop gain of the amplifier that will reduce the phase margin resulting in:
1. Peaking in the frequency response.
2. Overshoot, undershoot, and ringing in the time domain response with a pulse or square-wave signal.
3. May lead to instability or oscillation.
Inserting RO will compensate the phase shift and restore the phase margin, but it will also limit bandwidth. The circuit shown in Figure 68 is used to test for best RO versus capacitive loads, CL, with a capacitance placed differential across the VOUT+ and VOUT- along with 2 kΩ load resistor, and the output is measure with a differential probe. Figure 77 shows the optimum values of RO versus capacitive loads, CL, and Figure 78 shows the frequency response with various values. Performance is the same on both 2.7 V and 5 V supply.