OPA313
OPA2313
OPA4313
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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.
V+
IOVERLOAD
10-mA max
VOUT
Device
VIN
5 kW
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
region [VCM < (V+) – 1.3 V] is given. This specification is the best indicator of the capability of the device when
the application requires use of one of the differential input pairs. Second, the CMRR over the entire common-
mode range is specified at (VCM = –0.2 V to 5.7 V). This last value includes the variations seen through the
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 kΩ, 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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