OPA333_15 Datasheet, PDF (11/33 Pages) Texas Instruments – 1.8-V, microPower, CMOS Operational Amplifiers, Zero-Drift Series

OPA333
OPA2333
www.ti.com
SBOS351D – MARCH 2006 – REVISED NOVEMBER 2013
INTERNAL OFFSET CORRECTION
The OPA333 and OPA2333 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 μs using a proprietary technique. Upon power-up, the
amplifier requires approximately 100 μs 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 OPA333 and OPA2333 can be made to swing
to, or slightly below, ground on a single-supply power source. This swing is acheived with the use of the use of
another resistor and an additional, more negative power supply than the op amp negative supply. A pull-down
resistor can be connected between the output and the additional negative supply to pull the output down below
the value that the output would otherwise achieve, as shown in Figure 19.
V+ = +5 V
OPA333
V_OUT
V_IN
R_P = 20 kW
Op Amp V- = GND
-5 V
Additional
Negative
Supply
Figure 19. V_OUT Range to Ground
The OPA333 and OPA2333 have an output stage that allows the output voltage to be pulled to the negative
supply rail, or slightly below, using the technique previously described. This technique only works with some
types of output stages. The OPA333 and OPA2333 are characterized to perform with this technique; the
recommended resistor value is approximately 20 kΩ. Note that this configuration increases the current
consumption by several hundreds of microamps. Accuracy is excellent down to 0 V and as low as –2 mV.
Limiting and nonlinearity occurs below –2 mV, but excellent accuracy returns after the output is again driven
above –2 mV. Lowering the resistance of the pull-down resistor allows the op amp to swing even further below
the negative rail. Resistances as low as 10 kΩ can be used to achieve excellent accuracy down to –10 mV.
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Product Folder Links: OPA333 OPA2333
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