5 kW

10-mA max

V+

V

IN

V

OUT

I

OVERLOAD

Device

OPA313

OPA2313

OPA4313

www.ti.com

SBOS649C – SEPTEMBER 2012 – REVISED MARCH 2013

INPUT AND ESD PROTECTION

The OPA313 family incorporates internal electrostatic discharge (ESD) protection circuits on all pins. In the case

of input and output pins, this protection primarily consists of current-steering diodes connected between the input

and power-supply pins. These ESD protection diodes also provide in-circuit, input overdrive protection, as long

as the current is limited to 10 mA as stated in the Absolute Maximum Ratings. Figure 35 shows how a series

input resistor may be added to the driven input to limit the input current. The added resistor contributes thermal

noise at the amplifier input and its value should be kept to a minimum in noise-sensitive applications.

Figure 35. Input Current Protection

COMMON-MODE REJECTION RATIO (CMRR)

CMRR for the OPA313 is specified in several ways so the best match for a given application may be used; see

the Electrical Characteristics. First, the CMRR of the device in the common-mode range below the transition

the application requires use of one of the differential input pairs. Second, the CMRR over the entire common-

transition region (see Figure 7).

EMI SUSCEPTIBILITY AND INPUT FILTERING

Operational amplifiers vary with regard to the susceptibility of the device to electromagnetic interference (EMI). If

conducted EMI enters the op amp, the dc offset observed at the amplifier output may shift from its nominal value

while EMI is present. This shift is a result of signal rectification associated with the internal semiconductor

junctions. While all op amp pin functions can be affected by EMI, the signal input pins are likely to be the most

susceptible. The OPA313 operational amplifier family incorporate an internal input low-pass filter that reduces the

amplifiers response to EMI. Both common-mode and differential mode filtering are provided by this filter. The

filter is designed for a cutoff frequency of approximately 35 MHz (–3 dB), with a roll-off of 20 dB per decade.

Texas Instruments has developed the ability to accurately measure and quantify the immunity of an operational

amplifier over a broad frequency spectrum extending from 10 MHz to 6 GHz. The EMI rejection ratio (EMIRR)

metric allows op amps to be directly compared by the EMI immunity. Figure 33 illustrates the results of this

testing on the OPA313 family. Detailed information can also be found in the application report, EMI Rejection

Ratio of Operational Amplifiers (SBOA128), available for download from www.ti.com.

RAIL-TO-RAIL OUTPUT

Designed as a micro-power, low-noise operational amplifier, the OPA313 delivers a robust output drive capability.

A class AB output stage with common-source transistors is used to achieve full rail-to-rail output swing capability.

For resistive loads up to 10 k

Ω, the output swings typically to within 5 mV of either supply rail regardless of the

power-supply voltage applied. Different load conditions change the ability of the amplifier to swing close to the

rails; refer to the typical characteristic graph, Output Voltage Swing vs Output Current.

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Product Folder Links: OPA313 OPA2313 OPA4313