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OPA380

OPA2380

SBOS291G − NOVEMBER 2003 − REVISED SEPTEMBER 2007

www.ti.com

APPLICATIONS INFORMATION

BASIC OPERATION

The OPA380 is a high-performance transimpedance

amplifier with very low 1/f noise. As a result of its unique

architecture, the OPA380 has excellent long-term input

voltage offset stability—a 300-hour life test at 150

°C

demonstrated

randomly

distributed

variation

approximately equal to measurement repeatability of

µV.

The OPA380 performance results from an internal

auto-zero amplifier combined with a high-speed

amplifier. The OPA380 has been designed with circuitry

to improve overload recovery and settling time over a

traditional composite approach. It has been specifically

designed and characterized to accommodate circuit

options to allow 0V output operation (see Figure 3).

The OPA380 is used in inverting configurations, with the

noninverting input used as a fixed biasing point.

Figure 1 shows the OPA380 in a typical configuration.

Power-supply pins should be bypassed with 1

µF ceramic

or tantalum capacitors. Electrolytic capacitors are not

recommended.

OPA380

OUT

(1)

(0.5V to 4.4V)

BIAS =0.5V

+5V

µF

NOTE: (1) V

OUT = 0.5V in dark conditions.

Figure 1. OPA380 Typical Configuration

OPERATING VOLTAGE

The OPA380 series op amps are fully specified from

2.7V to 5.5V over a temperature range of −40

°C to

+125

°C. Parameters that vary significantly with operat-

ing voltages or temperature are shown in the Typical

Characteristics.

INTERNAL OFFSET CORRECTION

The OPA380 series op amps use an auto-zero topology

with a time-continuous 90MHz op amp in the signal

path. This amplifier is zero-corrected every 100

µs using

a proprietary technique. Upon power-up, the amplifier

requires approximately 400

µs to achieve specified VOS

accuracy, which includes one full auto-zero cycle of

approximately 100

µs and the start-up time for the bias

circuitry. Prior to this time, the amplifier will function

properly but with unspecified offset voltage.

This design has virtually no aliasing and very low noise.

Zero correction occurs at a 10kHz rate, but there is very

little fundamental noise energy present at that

frequency due to internal filtering.

For all practical

purposes, any glitches have energy at 20MHz or higher

and are easily filtered, if required. Most applications are

not sensitive to such high-frequency noise, and no

filtering is required.

INPUT VOLTAGE

The input common-mode voltage range of the OPA380

series extends from V− to (V+) – 1.8V. With input

signals above this common-mode range, the amplifier

will no longer provide a valid output value, but it will not

latch or invert.

INPUT OVERVOLTAGE PROTECTION

Device inputs are protected by ESD diodes that will

conduct if the input voltages exceed the power supplies

by more than approximately 500mV. Momentary

voltages greater than 500mV beyond the power supply

can be tolerated if the current is limited to 10mA. The

OPA380 series feature no phase inversion when the

inputs extend beyond supplies if the input is current

limited.

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