Datasheet

LM8272
www.ti.com SNOS515D –OCTOBER 2000–REVISED MARCH 2013
DRIVING CAPACTIVE LOADS:
The LM8272 is specifically designed to drive unlimited capacitive loads without oscillations (see Settling Time
and Slew Rate vs. Cap load plot, Figure 27). In addition, the output current handling capability of the device
allows for good slewing characteristics even with large capacitive loads (Settling Time and Slew Rate vs. Cap
Load plot). 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 Settling Time and Slew Rate vs. Cap Load plot, (Figure 27),
two distinct regions can be identified. Below about 10,000pF, the output Slew Rate is solely determined by the
Op Amp's compensation capacitor value and available current into that capacitor. Beyond 10nF, the Slew Rate is
determined by the Op Amp's available output current. An estimate of positive and negative slew rates for loads
larger than 100nF can be made by dividing the short circuit current value by the capacitor.
ESTIMATING THE OUTPUT VOLTAGE SWING
It is important to keep in mind that the steady state output current will be less than the current available when
there is an input overdrive present. For steady state conditions, Figure 39 and Figure 40 plots can be used to
predict the output swing. These plots also show several load lines corresponding to loads tied between the
output and ground. In each case, the intersection of the device plot at the appropriate temperature with the load
line would be the typical output swing possible for that load. For example, a 600Ω load can accommodate an
output swing to within 100mV of V
−
and to 250mV of V
+
(V
S
= ±5V) corresponding to a typical 9.65V
PP
unclipped
swing.
Figure 39. Steady State Output Sourcing Characteristics with Load Lines
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