MAX4249 Ver la hoja de datos (PDF) - Maxim Integrated

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MAX4249

SOT23 / Single-Supply / Low-Noise / Low-Distortion / Rail-to-Rail Op Amps

Maxim Integrated 

SOT23, Single-Supply, Low-Noise,

Low-Distortion, Rail-to-Rail Op Amps

Applications Information

The MAX4249–MAX4257 combine good driving capa-

bility with ground-sensing input and rail-to-rail output

operation. With their low distortion, low noise and low

power consumption, they are ideal for use in portable

instrumentation systems and other low-power, noise-

sensitive applications.

4.25V

VOUT

0

OV

4.45V

0

AV = +1

VDD = +5V

RL = 10kΩ

VIN

-200mV

20µs/div

Figure 3. Overdriven Input Showing No Phase Reversal

5V

VOUT

1V/

div

0V VDD = +5V

RL = 10kΩ

AV = +10

f = 1kHz

200µs/div

Figure 4. Rail-to-Rail Output Operation

RISO

VOUT

CL

MAX4250

VIN

MAX4251

MAX4252

MAX4253

MAX4254

Figure 5. Capacitive-Load Driving Circuit

Ground-Sensing and

Rail-to-Rail Outputs

The common-mode input range of the MAX4249–

MAX4257 extends down to ground, and offers excellent

common-mode rejection. These devices are guaran-

teed not to undergo phase reversal when the input is

overdriven (Figure 3).

Figure 4 showcases the true rail-to-rail output operation

of the amplifier, configured with AV = 10V/V. The output

swings to within 8mV of the supplies with a 10kΩ load,

making the devices ideal in low-supply-voltage applica-

tions.

Output Loading and Stability

Even with their low quiescent current of 400µA, these

amplifiers can drive 1kΩ loads while maintaining excel-

lent DC accuracy. Stability while driving heavy capaci-

tive loads is another key feature.

These devices maintain stability while driving loads up

to 400pF. To drive higher capacitive loads, place a

small isolation resistor in series between the output of

the amplifier and the capacitive load (Figure 5). This

resistor improves the amplifier’s phase margin by iso-

lating the capacitor from the op amp’s output.

Reference Figure 6 to select a resistance value that will

ensure a load capacitance that limits peaking to <2dB

(25%). For example, if the capacitive load is 1000pF,

the corresponding isolation resistor is 150Ω. Figure 7

shows that peaking occurs without the isolation resistor.

Figure 8 shows the unity-gain bandwidth vs. capacitive

load for the MAX4250–MAX4254.

Power Supplies and Layout

The MAX4249–MAX4257 operate from a single +2.4V

to +5.5V power supply or from dual supplies of ±1.20V

to ±2.75V. For single-supply operation, bypass the

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