PCH2

PCH1

IS1

VIN+

VIN±

e-trim

TM

Charge Pump

±Vsupply

-0.5

3

2

1

0

-1

-2

-3

InputCommon-ModeVoltage(V)

6.0

0

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

+V

-V

22

OPA325, OPA2325, OPA4325

SBOS637D – OCTOBER 2016 – REVISED JUNE 2019

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Product Folder Links: OPA325 OPA2325 OPA4325

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Copyright © 2016–2019, Texas Instruments Incorporated

Typical Application (continued)

The N-channel pair is active for input voltages close to the positive rail, typically (V+) – 1 V to 200 mV above the

positive supply, and the P-channel pair is on for inputs from 200 mV below the negative supply to approximately

(V+) – 1 V. There is a small transition region, typically (V+) – 1.1 V to (V+) – 0.9 V, in which both pairs are on.

This transition region is shown in Figure 48 for a traditional rail-to-rail input CMOS amplifier. Within this transition

region, PSRR, CMRR, offset voltage, offset drift, and THD can be degraded when compared to device operation

outside of this region.

Figure 48. Input Offset Voltage vs Common-Mode Voltage

(For Traditional Rail-to-Rail Input CMOS Amplifiers)

The OPAx325 amplifiers include an internal charge pump that powers the amplifier input stage with an internal

supply rail that is higher than the external power supply. The internal supply rail allows a single differential pair to

operate and to be linear across the entire input common-mode voltage range, as shown in Table 1.

Figure 49. Single Differential Input Pair with a Charge Pump (Zero-Crossover)