OPA310 datasheet(27/55 Pages) TI

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8.3 Feature Description

8.3.1 Operating Voltage

The OPAx310 series of operational amplifiers is fully specified from 1.8 V to 5.5 V and is tested for amplifier

operation from 1.5 V to 1.8 V. In addition, many specifications apply from –40°C to 125°C. Parameters that

vary significantly with operating voltages or temperature are provided in the Typical Characteristics. TI highly

recommends to bypass power-supply pins with at least 0.01-μF ceramic capacitors.

8.3.2 Rail-to-Rail Input

The input common-mode voltage range of the OPAx310 series extends to either supply rails. This is true even

when operating at the ultra-low supply voltage of 1.5 V, all the way up to the standard supply voltage of 5.5 V.

This performance is achieved with a complementary input stage: an N-channel input differential pair in parallel

with a P-channel differential pair. Refer to the Functional Block Diagram for more details.

For most amplifiers with a complementary input stage, one of the input pairs, usually the P-channel input pair,

is designed to deliver slightly better performance in terms of input offset voltage, offset drift over the N-channel

pair. Consequently, the P-channel pair is designed to cover the majority of the common mode range with the

N-channel pair slated to slowly take over at a certain threshold voltage from the positive rail. Just after the

threshold voltage, both the input pairs are in operation for a small range referred to as the transition region.

Beyond this region, the N-channel pair completely takes over. Within the transition region, PSRR, CMRR, offset

voltage, offset drift, and THD can be degraded compared to device operation outside this region. Hence, most

applications generally prefer operating in the P-channel input range where the performance is slightly better.

For the OPAx310, the P-channel pair is typically active for input voltages from (V–) to (V+) – 0.4 V and the

N-channel pair is typically active for input voltages from the positive supply to (V+) – 0.4 V. The transition region

occurs typically from (V+) – 0.5 V to (V+) – 0.3 V, in which both pairs are on. These voltage levels mentioned

above can vary with process variations associated with threshold voltage of transistors. In the OPAx310, 200-mV

transition region mentioned above can vary up to 200 mV in either direction. Thus, the transition region (both

stages on) can range from (V+) – 0.7 V to (V+) – 0.5 V on the low end, up to (V+) – 0.3 V to (V+) – 0.1 V on the

high end.

Recollecting the fact that a P-channel input pair usually offers better performance over a N-channel input

pair, the OPAx310 is designed to offer a much wider P-channel input pair range, in comparison to most

complimentary input amplifiers in the industry. A side-by-side comparison of the OPAx310 and the TLV900x

is provided below. Note that the TLV900x is designed for P-channel pair operation only until 1.4 V from the

positive rail, while the OPAx310 is designed for P-channel pair operation until 0.7 V from the positive rail. This

additional 700 mV of P-channel input pair range for the OPAx310 is particularly useful when operating at lower

supply voltages (1.5 V, 1.8 V, and so forth) where the P-channel input range usually gets limited to a great

extent.

Thus the wide common mode swing of input signal can be accommodated more easily within the P-channel

input pair of the OPAx310, while likely avoiding the transition region, thereby maintaining linearity.

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OPA310, OPA2310, OPA4310

SBOSAA1C – APRIL 2022 – REVISED SEPTEMBER 2022

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