OPA2335M Datasheet, PDF (9/16 Pages) Burr-Brown (TI) – 0.05 mV/°C MAX, SINGLE-SUPPLY CMOS OPERATIONAL AMPLIFIER ZERO-DRIFT SERIES

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APPLICATION INFORMATION
OPA2335M
SGLS320 – SEPTEMBER 2006
The OPA2335 op amp is unity-gain stable and free from unexpected output phase reversal. It uses auto-zeroing
techniques to provide low offset voltage and very low drift over time and temperature.
Good layout practice mandates use of a 0.1-µF capacitor placed closely across the supply pins.
For lowest offset voltage and precision performance, circuit layout and mechanical conditions should be
optimized. Avoid temperature gradients that create thermoelectric (Seebeck) effects in thermocouple junctions
formed from connecting dissimilar conductors. These thermally-generated potentials can be made to cancel by
assuring that they are equal on both input terminals.
• Use low thermoelectric-coefficient connections (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 µV/°C or higher, depending on materials used.
OPERATING VOLTAGE
The OPA2335 op amp operates over a power-supply range of 2.7 V to 5.5 V (±1.35 V to ±2.75 V). Supply
voltages higher than 7 V (absolute maximum) can permanently damage the amplifier. Parameters that vary over
supply voltage or temperature are shown in the Typical Characteristics section of this data sheet.
INPUT VOLTAGE
The input common-mode range extends from (V–) – 0.1 V to (V+) – 1.5 V. For normal operation, the inputs must
be limited to this range. The common-mode rejection ratio is only valid within the valid input common-mode
range. A lower supply voltage results in lower input common-mode range; therefore, attention to these values
must be given when selecting the input bias voltage. For example, when operating on a single 3-V power
supply, common-mode range is from 0.1 V below ground to half the power-supply voltage.
Normally, input bias current is approximately 70 pA; however, input voltages exceeding the power supplies can
cause excessive current to flow in 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 is easily accomplished with an input resistor, as
shown in Figure 21.
Current-limiting resistor
required if input voltage
exceeds supply rails by
³ 0.5 V.
I_OVERLOAD
10 mA max
V_IN
5 kW
5V
OPA335
V_OUT
S0146-01
Figure 21. Input Current Protection
INTERNAL OFFSET CORRECTION
The OPA2335 op amp uses an auto-zero topology with a time-continuous 2-MHz op amp in the signal path. This
amplifier is zero-corrected every 100 µs using a proprietary technique. Upon power-up, the amplifier requires
one full auto-zero cycle of approximately 100 µs to achieve specified V_OS accuracy. Prior to this time, the
amplifier functions properly, but with unspecified offset voltage.
This design has remarkably little aliasing and noise. Zero correction occurs at a 10-kHz rate, but there is virtually
no fundamental noise energy present at that frequency. For all practical purposes, any glitches have energy at
20 MHz or higher and are easily filtered, if required. Most applications are not sensitive to such high-frequency
noise, and no filtering is required.
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