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TLV522

SNOSD27 – MAY 2016

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Copyright © 2016, Texas Instruments Incorporated

Device Functional Modes (continued)

Figure 22. Supply Current Change Over Common Mode at 5 V

For the lowest supply current operation, keep the input common mode range between V- and 1 V below V+.

7.4.3 Design Optimization With Rail-To-Rail Input

In most applications, operation is within the range of only one differential pair. However, some applications can

subject the amplifier to a common-mode signal in the transition region. Under this condition, the inherent

mismatch between the two differential pairs may lead to degradation of the CMRR and THD. The unity-gain

buffer configuration is the most problematic as it will traverse through the transition region if a sufficiently wide

input swing is required.

7.4.4 Design Optimization for Nanopower Operation

When designing for ultra-low power, choose system components carefully. To minimize current consumption,

select large-value resistors. Any resistors will react with stray capacitance in the circuit and the input capacitance

of the operational amplifier. These parasitic RC combinations can affect the stability of the overall system. A

feedback capacitor may be required to assure stability and limit overshoot or gain peaking.

When possible, use AC coupling and AC feedback to reduce static current draw through the feedback elements.

Use film or ceramic capacitors since large electolytics may have static leakage currents in the tens to hundreds

of nanoamps.

7.4.5 Common-Mode Rejection

The CMRR for the TLV522 is specified in two ways so the best match for a given application may be used. First,

the CMRR of the device in the common-mode range below the transition region (VCM < (V+) – 1.1 V) is given.

This specification is the best indicator of the capability of the device when the application requires use of one of

the differential input pairs. Second, the CMRR at VS = 3.3 V over the entire common-mode range is specified.

7.4.6 Output Stage

The TLV522 output voltage swings 3 mV from rails at 3.3 V supply, which provides the maximum possible

dynamic range at the output. This is particularly important when operating on low supply voltages.

The TLV522 Maximum Output Voltage Swing defines the maximum swing possible under a particular output

load.

7.4.7 Driving Capacitive Load

The TLV522 is internally compensated for stable unity gain operation, with a 8 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’s 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 under damped which causes peaking in the transfer and, when there is too much peaking, the

op amp might start oscillating.