LOG112 datasheet(10/26 Pages) TI2

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OPA380

OPA2380

SBOS291G − NOVEMBER 2003 − REVISED SEPTEMBER 2007

www.ti.com

OUTPUT RANGE

The OPA380 is specified to swing within at least 600mV

of the positive rail and 100mV of the negative rail with

a 2k

Ω load with excellent linearity. Swing to the negative

rail while maintaining good linearity can be extended to

0V—see the section, Achieving Output Swing to

Ground. See the Typical Characteristic curve, Output

Voltage Swing vs Output Current.

The OPA380 can swing slightly closer than specified to

the positive rail; however, linearity will decrease and a

high-speed overload recovery clamp limits the amount

of positive output voltage swing available, as shown in

Figure 2.

−5

−10

−15

−20

OFFSET VOLTAGE vs OUTPUT VOLTAGE

OUT (V)

123

S =5V

P =2kΩ connected to −5V

L =2kΩ connected to VS /2

Effect of clamp

Figure 2. Effect of High-Speed Overload

Recovery Clamp on Output Voltage

OVERLOAD RECOVERY

The OPA380 has been designed to prevent output

saturation. After being overdriven to the positive rail, it

will typically require only 100ns to return to linear

operation. The time required for negative overload

recovery is greater, unless a pull-down resistor

connected to a more negative supply is used to extend

the output swing all the way to the negative rail—see the

following section, Achieving Output Swing to Ground.

ACHIEVING OUTPUT SWING TO GROUND

Some applications require output voltage swing from

0V to a positive full-scale voltage (such as +4.096V)

with excellent accuracy. With most single-supply op

amps,

problems

arise

when

the

output

signal

approaches 0V, near the lower output swing limit of a

single-supply op amp. A good single-supply op amp

may swing close to single-supply ground, but will not

reach 0V.

The output of the OPA380 can be made to swing to

ground, or slightly below, on a single-supply power

source. This extended output swing requires the use of

another resistor and an additional negative power

supply. A pull-down resistor may be connected between

the output and the negative supply to pull the output

down to 0V. See Figure 3.

OPA380

OUT

P =2kΩ

V+ = +5V

− =Gnd

P = −5V

Negative Supply

Figure 3. Amplifier with Optional Pull-Down

Resistor to Achieve VOUT = 0V

The OPA380 has an output stage that allows the output

voltage to be pulled to its negative supply rail using this

technique. However, this technique only works with

some types of output stages. The OPA380 has been

designed to perform well with this method. Accuracy is

excellent down to 0V. Reliable operation is assured over

the specified temperature range.

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