SOT23, Very High Precision, 3V/5V

Rail-To-Rail Op Amps

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Detailed Description

The MAX4236/MAX4237 are high-precision op amps

with a CMOS input stage and an excellent set of DC

and AC features. The combination of tight maximum

voltage offset, low offset tempco and very low input

current make them ideal for use in high-precision DC

circuits. They feature low-voltage operation, low-power

consumption, high-current drive with rail-to-rail output

swing and high-gain bandwidth product.

High Accuracy

The MAX4236/MAX4237 maximum input offset voltage

is 20µV (5µV, typ) for grade A version and 50µV for

grade B version at +25°C. The maximum temperature

coefficient of the offset voltage for grade A and B are

guaranteed to be 2µV/°C and 4.5µV/°C respectively.

The parts have an input bias current of 1pA. Noise

characteristics are 14nV/

√Hz, and a low frequency

noise (0.1Hz to 10Hz) of 0.2µVp-p. The CMRR is

102dB, and the PSRR is 120dB. The combination is

what is necessary for the design of circuits to process

signals while keeping high signal-to-noise ratios, as in

stages preceding high-resolution converters, or when

they are produced by sensors or transducers generat-

ing very small outputs.

Rail-to-Rail Outputs, Ground-Sensing Input

rejection. Beyond this range, the amplifier output is a

nonlinear function of the input, but does not undergo

phase reversal or latch-up (see Typical Operating

Characteristics).

The output swings to within 150mV of the power-supply

rails with a 1k

Ω load. The input ground sensing and the

rail-to-rail output substantially increase the dynamic

range.

Power-Up and Shutdown Mode

The MAX4236/MAX4237 have a shutdown option.

When the shutdown pin (SHDN) is pulled low, the sup-

ply current drops to 0.1µA, and the amplifiers are dis-

abled with the output in a high-impedance state. Pulling

SHDN high enables the amplifiers. The turn-on time for

the amplifiers to come out of shutdown is 4µs.

Applications Information

As described above, the characteristics of the

MAX4236/MAX4237 are excellent for high-precision/

accuracy circuitry, and the high impedance, low-cur-

rent, low-offset, and noise specifications are very

attractive for piezoelectric transducers applications. In

these applications, the sensors generate an amount of

electric charge proportional to the changes in the

mechanical stress applied to them. These charges are

transformed into a voltage proportional to the applied

force by injecting them into a capacitance and then

amplifying the resulting voltage. The voltage is an

inverse function of the capacitance into which the

charges generated by the transducer/ sensor are

injected. This capacitance and the resistance that dis-

charges it, define the low-frequency response of the

circuit. It is desirable, once the preferred low-frequency

response is known, to maintain the capacitance as low

as possible, because the amount of necessary

upstream amplification (and the signal-to-noise ratio

deterioration) is directly proportional to the capacitance

value. The MAX4236/MAX4237 high-impedance, low-

Pin Description

PIN

SOT23

SO/µMAX

NAME

FUNCTION

1

6

OUT

Amplifier Output

24

Negative Power Supply. Bypass with a 0.1

µF capacitor to ground. Connect to GND

for single-supply operation.

3

3

IN+

Noninverting Amplifier Input

4

2

IN-

Inverting Amplifier Input

58

SHDN

to enter the shutdown mode.

67

Positive Supply Input. Bypass with a 0.1

µF capacitor to ground.

—

1, 5

N.C.

No Connection. Not internally connected.