OPA2314-EP Datasheet, PDF (13/23 Pages) Texas Instruments – 3-MHz, LOW-POWER, LOW-NOISE, RRI/O, 1.8-V CMOS OPERATIONAL AMPLIFIER

OPA2314-EP
www.ti.com
SBOS597 – SEPTEMBER 2012
Input and ESD Protection
The OPA2314 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.
I_OVERLOAD
10mA max
V_IN
5kW
V+
OPA2314
V_OUT
Figure 35. Input Current Protection
Common-Mode Rejection Ratio (CMRR)
CMRR for the OPA2314 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 8).
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 OPA2314 operational amplifier incorporates 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 80 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 shows the results of this testing
on the OPAx314. Detailed information can also be found in the application report, EMI Rejection Ratio of
Operational Amplifiers (SBOA128), available for download from the TI website.
Rail-to-Rail Output
Designed as a micro-power, low-noise operational amplifier, the OPA2314 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, as can be seen in the typical characteristic graph, Output Voltage Swing vs Output
Current.
Copyright © 2012, Texas Instruments Incorporated
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