LM7321, LM7322

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SNOSAW8D – MAY 2008 – REVISED MARCH 2013

Figure 66.

−SR vs. Capacitive Load

The combination of these features is ideal for applications such as TFT flat panel buffers, A/D converter input

amplifiers, etc.

However, as in most op amps, addition of a series isolation resistor between the op amp and the capacitive load

improves the settling and overshoot performance.

Output current drive is an important parameter when driving capacitive loads. This parameter will determine how

fast the output voltage can change. Referring to the Slew Rate vs. Capacitive Load Plots (Typical Performance

Characteristics section), two distinct regions can be identified. Below about 10,000 pF, the output Slew Rate is

solely determined by the op amp’s compensation capacitor value and available current into that capacitor.

Beyond 10 nF, the Slew Rate is determined by the op amp’s available output current. Note that because of the

lower output sourcing current compared to the sinking one, the Slew Rate limit under heavy capacitive loading is

determined by the positive transitions. An estimate of positive and negative slew rates for loads larger than 100

nF can be made by dividing the short circuit current value by the capacitor.

For the LM7321/LM7321Q/LM7322/LM7322Q, the available output current increases with the input overdrive.

Referring to Figure 67 and Figure 68, Output Short Circuit Current vs. Input Overdrive, it can be seen that both

sourcing and sinking short circuit current increase as input overdrive increases. In a closed loop amplifier

configuration, during transient conditions while the fed back output has not quite caught up with the input, there

will be an overdrive imposed on the input allowing more output current than would normally be available under

steady state condition. Because of this feature, the op amp’s output stage quiescent current can be kept to a

minimum, thereby reducing power consumption, while enabling the device to deliver large output current when

the need arises (such as during transients).

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Product Folder Links: LM7321 LM7322