accuracy. For example, with RL = 25kΩ, OPA336 series op
amps perform well with capacitive loads in excess of 1000pF,
as shown in Figure 4. Without RS, capacitive load drive is
typically 350pF for these conditions, as shown in Figure 5.
Direct Current (DC) error at the output; however, this error
may be insignificant. For instance, with RL = 100kΩ and
RS = 100Ω, there is only about a 0.1% error at the output.
Figure 5 shows the recommended operating regions for the
OPA336. Decreasing the load resistance generally improves
capacitive load drive. Figure 5 also illustrates how stability
differs depending on where the resistive load is connected.
With G = +1 and RL = 10kΩ connected to VS/2, the OPA336
can typically drive 500pF. Connecting the same load to
ground improves capacitive load drive to 1000pF.
RS = 100Ω, Load = 2kΩ || 1000pF, VS = +5V
10k
Operation Above Selected Gain
Curve Not Recommended
G = +2
G = +1
RL to Ground
RL to Ground
1k
50µs/div
FIGURE 4. Small-Signal Step Response Using Series Re-
sistor to Improve Capacitive Load Drive.
G = +1
L to VS/2
R
VS = +5V, VO = VS/2
Alternatively, the resistor may be connected in series with
the output outside of the feedback loop. However, if there is
a resistive load parallel to the capacitive load, it and the
series resistor create a voltage divider. This introduces a
100
5
10
100
Resistive Load (kΩ)
FIGURE 5. Stability—Capacitive Load vs Resistive Load.
OPA336, 2336, 4336
8
SBOS068C
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