MAX4236/MAX4237
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
The input common-mode range extends from (V
EE
-
0.15V) to (V
CC
- 1.2V) with excellent common-mode
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 1kΩ 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
Negative Power Supply. Bypass with a 0.1µF capacitor to ground. Connect to GND
for single-supply operation.
Shutdown Input. Do not leave floating. Connect to V
to enter the shutdown mode.
Positive Supply Input. Bypass with a 0.1µF capacitor to ground.
