–0.5

Common-Mode Voltage (V)

OFFSET VOLTAGE

vs FULL COMMON-MODE VOLTAGE RANGE

0

V–

0.5

1.5

1

2.5

2

3.5

3

4.5

5

4

5.5

2

1.5

1

0.5

0

–0.5

–1

–1.5

–2

V+

5 kW

10-mA max

V+

V

IN

V

OUT

I

OVERLOAD

Device

OPA348-Q1, OPA2348-Q1, OPA4348-Q1

www.ti.com

SBOS465C – JANUARY 2009 – REVISED JANUARY 2016

Feature Description (continued)

7.3.4 Input and ESD Protection

The OPAx348-Q1 family of devices 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 table. Figure 21

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 should be kept to a minimum in noise-sensitive

applications.

Figure 21. Input Current Protection

7.3.5 Common-Mode Rejection Ratio (CMRR)

CMRR for the OPAx348-Q1 family of devices is specified in several ways so the best match for a given

application may be used; see the Electrical Characteristics table. 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 22).

7.3.6 Common-Mode Voltage Range

The input common-mode voltage range of the OPAx348-Q1 device extends 200 mV beyond the supply rails.

This extended range is achieved with a complementary input stage—an N-channel input differential pair in

parallel with a P-channel differential pair. The N-channel pair is active for input voltages close to the positive rail,

typically (V+) – 1.2 V to 300 mV above the positive supply, while the P-channel pair is on for inputs from 300 mV

below the negative supply to approximately (V+) – 1.4 V. A small transition region exists, typically (V+) – 1.4 V to

(V+) – 1.2 V, in which both pairs are on. This 200-mV transition region, shown in Figure 22, can vary ±300 mV

with process variation. Thus, the transition region (both stages on) can range from (V+) – 1.7 V to (V+) – 1.5 V

on the low end, up to (V+) – 1.1 V to (V+) – 0.9 V on the high end. Within the 200-mV transition region, PSRR,

CMRR, offset voltage, offset drift, and THD may be degraded compared to operation outside this region.

Figure 22. Behavior of Typical Transition Region at Room Temperature

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Product Folder Links: OPA348-Q1 OPA2348-Q1 OPA4348-Q1