OPA316-Q1 Datasheet, PDF (19/39 Pages) Texas Instruments – 10-MHz, Rail-to-Rail Input/Output, Low-Voltage, 1.8-V CMOS Operational Amplifier

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OPA316-Q1, OPA2316-Q1, OPA4316-Q1
SBOS841A – NOVEMBER 2016 – REVISED JANUARY 2017
Feature Description (continued)
7.3.2 Rail-to-Rail Input
The input common-mode voltage range of the OPAx316-Q1 series extends 200 mV beyond the supply rails for
supply voltages greater than 2.5 V. This performance is achieved with a complementary input stage: an N-
channel input differential pair in parallel with a P-channel differential pair, as shown in the Functional Block
Diagram. The N-channel pair is active for input voltages close to the positive rail, typically (V+) – 1.4 V to 200 mV
above the positive supply, whereas the P-channel pair is active for inputs from 200 mV below the negative
supply to approximately (V+) – 1.4 V. There is a small transition region, typically (V+) – 1.2 V to (V+) – 1 V, in
which both pairs are on. This 200-mV transition region can vary up to 200 mV with process variation. Thus, the
transition region (both stages on) can range from (V+) – 1.4 V to (V+) – 1.2 V on the low end, up to (V+) – 1 V to
(V+) – 0.8 V on the high end. Within this transition region, PSRR, CMRR, offset voltage, offset drift, and THD can
degrade compared to device operation outside this region.
7.3.3 Input and ESD Protection
The OPAx316-Q1 incorporates internal 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 provide in-circuit, input overdrive protection, as long as the current is limited to 10
mA, as stated in Absolute Maximum Ratings table. Figure 37 shows how a series input resistor can be added to
the driven input to limit the input current. The added resistor contributes thermal noise at the amplifier input and
the value must be kept to a minimum in noise-sensitive applications.
I_OVERLOAD
10-mA max
V_IN
5 kW
V+
Device
V_OUT
Figure 37. Input Current Protection
7.3.4 Common-Mode Rejection Ratio (CMRR)
CMRR for the OPAx316-Q1 is specified in several ways so the user can select the best match for a given
application, as shown in the Electrical Characteristics table. First, the data sheet gives the CMRR of the device in
the common-mode range below the transition region [V_CM < (V+) – 1.4 V]. This specification is the best indicator
of device capability when the application requires use of one of the differential input pairs. Second, the CMRR
over the entire common-mode range is specified at V_CM = –0.2 V to 5.7 V for V_S = 5.5 V. This last value includes
the variations shown in Figure 4 through the transition region.
7.3.5 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 operational amplifier, the dc offset observed at the amplifier output can shift from the
nominal value when EMI is present. This shift is a result of signal rectification associated with the internal
semiconductor junctions. Although EMI can affect all operational amplifier pin functions, the signal input pins are
likely to be the most susceptible. The OPA316-Q1 operational amplifier family incorporates an internal input low-
pass filter that reduces the amplifier response to EMI. This filter provides both common-mode and differential-
mode filtering. The filter is designed for a cutoff frequency of approximately 80 MHz (–3 dB), with a roll-off of 20
dB per decade.
TI 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 operational
amplifiers to be directly compared by the EMI immunity. Figure 35 illustrates the testing results on the OPAx316-
Q1. For more information, see EMI Rejection Ratio of Operational Amplifiers.
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