Single/Dual/Quad, Wide-Bandwidth, Low-Power,

Single-Supply, Rail-to-Rail I/O Op Amps

10

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Rail-to-Rail Output Stage

The minimum output voltage is within millivolts of

ground for single-supply operation where the load is

voltage range and output voltage swing of a MAX4131

connected as a voltage follower. With a +3V supply

and the load tied to ground, the output swings from

0.00V to 2.90V. The maximum output voltage swing

depends on the load, but will be within 150mV of a +3V

supply, even with the maximum load (500

Ω to ground).

Driving a capacitive load can cause instability in most

high-speed op amps, especially those with low quies-

cent current. The MAX4130–MAX4134 have a high tol-

erance for capacitive loads. They are stable with

capacitive loads up to 160pF. Figure 4 gives the stable

operating region for capacitive loads. Figures 5 and 6

show the response with capacitive loads and the

results of adding an isolation resistor in series with the

output (Figure 7). The resistor improves the circuit’s

phase margin by isolating the load capacitor from the

op amp’s output.

IN

TIME (1

µs/div)

OUT

Figure 3. Rail-to-Rail Input/Output Voltage Range

500

0

50

100

150

200

300

350

400

450

0.1

1

100

10

LOAD RESISTANCE (k

Ω)

250

UNSTABLE

OPERATING

REGION

STABLE

OPERATING

REGION

Figure 4. Capacitive-Load Stability

IN

TIME (200ns/div)

OUT

Figure 5. MAX4131 Small-Signal Transient Response with

Capacitive Load

Figure 6. MAX4131 Transient Response to Capacitive Load

with Isolation Resistor

IN

TIME (500ns/div)

OUT