OPA690 datasheet(22/27 Pages) TI

22 / 27 page

OPA2613

SBOS249D − JUNE 2003− REVISED APRIL 2004

www.ti.com

Figure 12 shows a comparison of 2

• Input voltage to the

capacitor voltage. The transition time is set by the 70V/

µs

slew rate for the OPA2613. For this controlled dV/dT, the

charging current into the 5000pF load will be given by:

Slew Rate = IP/C

Solving for IP gives:

+ 5000pF

70V

ms + 350mA peak current

Time (100ns/div)

Capacitor Voltage

2X Input Voltage

70V/

µsSlew Rate

−1

−2

−3

−4

−5

−6

Figure 12. Large-Signal Capacitive Load Drive

At these larger capacitive loads, very low series R will

maintain stability

but some R is always required.

DISTORTION PERFORMANCE

The OPA2613 provides good distortion performance into

a 100

Ω load on ±6V supplies. Generally, until the

fundamental signal reaches high frequency or power

levels, the 2nd-harmonic dominates the distortion with a

negligible 3rd-harmonic component. Focusing then on the

2nd-harmonic, increasing the load impedance improves

distortion directly. Remember that the total load includes

the feedback network

in the noninverting configuration

(see Figure 1), this is the sum of RF + RG, whereas in the

inverting configuration, it is just RF. Also, providing an

additional supply decoupling capacitor (0.01

µF) between

the supply pins (for bipolar operation) improves the

2nd-order distortion slightly (3dB to 6dB).

In most op amps, increasing the output voltage swing

increases harmonic distortion directly. The Typical

Characteristics show the 2nd-harmonic increasing at a

little less than the expected 2x rate whereas the

3rd-harmonic increases at a little less than the expected 3x

rate. Where the test power doubles, the difference

between it and the 2nd-harmonic decreases less than the

expected 6dB, whereas the difference between it and the

3rd-harmonic decreases by less than the expected 12dB.

Operating differentially will suppress the 2nd-order

harmonics below the 3rd.

Operating as a differential I/O stage will also suppress the

2nd-harmonic distortion.

NOISE PERFORMANCE

Wideband voltage-feedback op amps generally have a

lower output noise than comparable current-feedback op

amps. The OPA2613 offers an excellent balance between

voltage and current noise terms to achieve low output

noise. The input voltage noise (1.8nV/

√Hz) is lower than

most unity-gain stable, wideband voltage-feedback op

amps. The op amp input voltage noise and the two input

current noise terms combine to give low output noise

under a wide variety of operating conditions. Figure 13

shows the op amp noise analysis model with all the noise

terms included. In this model, all noise terms are taken to

be noise voltage or current density terms in either nV/

√Hz

or pA/

√Hz.

4kT

1/2

OPA2613

IBI

4kT = 1.6E

−20J

at 290

√4kTR

Figure 13. Op Amp Noise Analysis Model

The total output spot noise voltage can be computed as the

square root of the sum of all squared output noise voltage

contributors. Equation 17 shows the general form for the

output noise voltage using the terms given in Figure 13.

O +

ENI

2 ) I

) 4kTR

NG2

) I

) 4kTR

FNG

Dividing this expression by the noise gain (NG = (1 + RF/RG))

gives the equivalent input-referred spot noise voltage at the

noninverting input, as shown in Equation 18.

N +

2 ) I

) 4kTR

S )

)

4kTR

Evaluating these two equations for the OPA2613 circuit

and component values (see Figure 1) gives a total output

spot noise voltage of 6.34nV/

√Hz and a total equivalent

input spot noise voltage of 3.2nV/

√Hz. This total input

referred spot noise voltage is higher than the 1.8nV/

√Hz

specification for the op amp voltage noise alone. This

reflects the noise added to the output by the inverting

current noise times the feedback resistor.

(16)

(17)

(18)

OPA690 Datasheet(PDF) 22 Page - Texas Instruments

OPA690 Datasheet(HTML) 22 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Datasheet Download

Link URL