The MAX492/MAX494/MAX495 can drive capacitive

loads in excess of 1000pF under certain conditions

(Figure 5). When driving capacitive loads, the greatest

potential for instability occurs when the op amp is

sourcing approximately 100µA. Even in this case, sta-

bility is maintained with up to 400pF of output capaci-

tance. If the output sources either more or less current,

stability is increased. These devices perform well with a

1000pF pure capacitive load (Figure 6). Figure 7 shows

the performance with a 500pF load in parallel with vari-

ous load resistors.

To increase stability while driving large capacitive

loads, connect a pull-up resistor at the output to

decrease the current that the amplifier must source. If

the amplifier is made to sink current rather than source,

stability is further increased.

Frequency stability can be improved by adding an out-

(Figure 8). This resistor improves the phase margin of

the circuit by isolating the load capacitor from the op

amp’s output. Figure 9a shows the MAX492 driving

≥ 100kΩ), while Figure 9b adds a 47Ω

isolation resistor.

Single/Dual/Quad, Micropower,

Single-Supply Rail-to-Rail Op Amps

______________________________________________________________________________________

13

50mV/div

50mV/div

10

µs/div

50mV/div

50mV/div

10

µs/div

MAX495

2

3

1k

1k

+5V

7

4

6

MAX49_

Figure 10. Power-Up Test Configuration

Figure 9b. Driving a 10,000pF Capacitive Load with a 47

Ω

Isolation Resistor

Figure 9a. Driving a 10,000pF Capacitive Load

Figure 8. Capacitive-Load Driving Circuit