8.1.1 Drive a Capacitive Load

The TLV6003 is internally compensated for stable unity-gain operation, with a 5.5-kHz typical gain bandwidth. However, the unity gain follower is the most sensitive configuration to capacitive load. The combination of a capacitive load placed directly on the output of an amplifier along with the amplifier output impedance creates a phase lag, which reduces the phase margin of the amplifier. If the phase margin is significantly reduced, the response will be underdamped, which causes peaking in the transfer function. This condition creates very low phase margin, and leads to excessive ringing or oscillations.

In order to drive heavy (> 50 pF) capacitive loads, an isolation resistor (R_ISO) must be used, as shown in Figure 31. By using this isolation resistor, the capacitive load is isolated from the amplifier output. The higher the value of R_ISO, the more stable the amplifier. If the value of R_ISO is sufficiently high, the feedback loop is stable, independent of the value of C_L. However, larger values of R_ISO result in reduced output swing and reduced output current drive. The recommended value for R_ISO is 30 kΩ to 50 kΩ.

Figure 31. Resistive Isolation of Capacitive Load