8.3.2 Lower Input Bias With Super-Beta Inputs

The OPAx205 have a super-beta input transistor architecture. In a transistor, the beta value is the ratio between

the current flowing into the base and the current flowing from the collector to the emitter. A super-beta transistor

is one where the beta value has been increased from several hundred to thousands. In a bipolar amplifier, the

input bias current is the current flowing into the base of the input transistor pair, as well as a small leakage

current that flows through the ESD diodes. A super-beta input reduces the input bias current of the amplifier. In

addition, the super-beta inputs lower the input current noise that is directly related to the input bias current of the

device. A comparison between the input bias current of the OPA2277 and the OPAx205 super-beta input bias

currents can be seen in Figure 8-4 and Figure 8-5.

125

Temperature ( °C)

–75

–50

–25

0

25

50

75

100

5

4

3

2

1

0

–1

–2

–3

–4

–5

Curves represent typical

production units.

Figure 8-4. OPA2277 Input Bias Current

Temperature (°C)

-50

-25

0

25

50

75

100

125

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

IBN

IBP

Figure 8-5. OPAx205 Super-Beta Input Bias Current

8.3.3 Overload Power Limiter

In many bipolar-based amplifiers, the output stage of the amplifier can draw significant (several milliamperes)

of quiescent current if the output voltage becomes clipped (that is, the output voltage becomes limited by the

negative or positive supply voltage). This condition can cause the system to enter a high-power consumption

state, and potentially cause oscillations between the power supply and signal chain. The OPAx205 have an

advanced output stage design that eliminates this problem. When the output voltage reaches either supply (V+

or V–), there is virtually no additional current consumption from the nominal quiescent current. This feature helps

eliminate any potential system problems when the signal chain is disrupted by large external transient voltage.

8.3.4 EMI Rejection

The OPAx205 use integrated electromagnetic interference (EMI) filtering to reduce the effects of EMI from

sources, such as wireless communications and densely populated boards with a mix of analog signal chain and

digital components. EMI immunity can be improved through circuit design techniques that improve the system

performance. Additional information can be found in the EMI Rejection Ratio of Operation Amplifiers application

report.

8.4 Device Functional Modes

The OPAx205 have a single functional mode and are operational with any supply between 4.5 V (±2.25 V) and

36 V (±18 V).

OPA205, OPA2205, OPA4205

SBOS962F – APRIL 2020 – REVISED MARCH 2023

www.ti.com

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