OPA2333-Q1 Datasheet, PDF (7/16 Pages) Texas Instruments – 1.8-V MICROPOWER CMOS OPERATIONAL AMPLIFIER ZERO-DRIFT SERIES

OPA2333-Q1
www.ti.com
SBOS463A – DECEMBER 2008 – REVISED JUNE 2010
APPLICATION INFORMATION
The OPA2333A op amps are unity-gain stable and free from unexpected output phase reversal. They use a
proprietary auto-calibration technique to provide low offset voltage and very low drift over time and temperature.
For lowest offset voltage and precision performance, circuit layout and mechanical conditions should be
optimized. Avoid temperature gradients that create thermoelectric (Seebeck) effects in the thermocouple
junctions formed from connecting dissimilar conductors. These thermally-generated potentials can be made to
cancel by ensuring they are equal on both input terminals. Other layout and design considerations include:
• Use low thermoelectric-coefficient conditions (avoid dissimilar metals)
• Thermally isolate components from power supplies or other heat sources
• Shield op amp and input circuitry from air currents, such as cooling fans
Following these guidelines will reduce the likelihood of junctions being at different temperatures, which can cause
thermoelectric voltages of 0.1 mV/°C or higher, depending on materials used.
Operating Voltage
The OPA2333A op amps operate over a power-supply range of 1.8 V to 5.5 V (±0.9 V to ±2.75 V). Supply
voltages higher than 7 V (absolute maximum) can permanently damage the device. Parameters that vary over
supply voltage or temperature are shown in the Typical Characteristics section of this data sheet.
Input Voltage
The OPA2333A input common-mode voltage range extends 0.1 V beyond the supply rails. The device is
designed to cover the full range without the troublesome transition region found in some other rail-to-rail
amplifiers.
Normally, input bias current is about 70 pA; however, input voltages exceeding the power supplies can cause
excessive current to flow into or out of the input pins. Momentary voltages greater than the power supply can be
tolerated if the input current is limited to 10 mA. This limitation is easily accomplished with an input resistor(see
Figure 1).
+5 V
I_OVERLOAD
10 mA max
V_IN
5 kW
(see Note)
1/2
OPA2333
V_OUT
NOTE: Current-limiting resistor required if input voltage exceeds supply rails by ≥ 0.5 V.
Figure 1. Input Current Protection
Internal Offset Correction
The OPA2333A op amps use an auto-calibration technique with a time-continuous 350-kHz op amp in the signal
path. This amplifier is zero corrected every 8 ms using a proprietary technique. Upon power up, the amplifier
requires approximately 100 ms to achieve specified V_OS accuracy. This design has no aliasing or flicker noise.
Achieving Output Swing to the Op Amp Negative Rail
Some applications require output voltage swings from 0 V to a positive full-scale voltage (such as 2.5 V) with
excellent accuracy. With most single-supply op amps, problems arise when the output signal approaches 0 V,
near the lower output swing limit of a single-supply op amp. A good single-supply op amp may swing close to
single-supply ground, but will not reach ground. The output of the OPA2333A can be made to swing to ground or
slightly below on a single-supply power source. To do so requires the use of another resistor and an additional,
more negative, power supply than the op amp negative supply. A pulldown resistor may be connected between
the output and the additional negative supply to pull the output down below the value that the output would
otherwise achieve (see Figure 2).
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