Low-Cost, 230MHz, Single/Quad Op Amps with

Rail-to-Rail Outputs and ±15kV ESD Protection

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9

Rail-to-Rail Outputs,

Ground-Sensing Inputs

rejection. Beyond this range, the amplifier output is a

nonlinear function of the input, but does not undergo

phase reversal or latchup.

The output swings to within 50mV of either power-sup-

ply rail with a 2k

Ω load. The input ground sensing and

the rail-to-rail output substantially increase the dynamic

Output Capacitive Loading and Stability

The MAX4385E/MAX4386E are optimized for AC perfor-

mance and do not drive highly reactive loads, which

decreases phase margin and may produce excessive

ringing and oscillation. Figure 2 shows a circuit that

eliminates this problem. Figure 3 is a graph of the

Figure 4 shows how a capacitive load causes exces-

sive peaking of the amplifier’s frequency response if

the capacitor is not isolated from the amplifier by a

resistor. A small isolation resistor (usually 10

Ω to 15Ω)

placed before the reactive load prevents ringing and

oscillation. At higher capacitive loads, the interaction of

the load capacitance and the isolation resistor controls

the AC performance. Figure 5 shows the effect of a

15

Ω isolation resistor on closed-loop response.

6

-4

100k

10M

100M

1M

1G

-2

FREQUENCY (Hz)

0

2

4

5

-3

-1

1

3

Figure 4. Small-Signal Gain vs. Frequency with Load

Capacitance and No Isolation Resistor

Figure 2. Driving a Capacitive Load Through an Isolation Resistor

9

11

10

13

12

15

14

16

0

200

100

300

400

50

250

150

350

450 500

ISOLATION RESISTANCE

vs. CAPACITIVE LOAD

Figure 3. Isolation Resistance vs. Capacitive Load

MAX438_E

3

-7

100k

10M

100M

1M

1G

-5

FREQUENCY (Hz)

-3

-1

1

2

-6

-4

-2

0

Ω

Figure 5. Small-Signal Gain vs. Frequency with Load

Capacitance and 27

Ω Isolation Resistor