OPA690 datasheet(31/45 Pages) TI

31 / 45 page

OPERATING SUGGESTIONS

OPTIMIZING RESISTOR VALUES

GBP

4 R C

p F D

2 R C

p F F

GBP

2 R C

p F D

-3dB

DESIGN-IN TOOLS

DEMONSTRATION FIXTURES

MACROMODELS AND APPLICATIONS

OPA4830

www.ti.com.................................................................................................................................................... SBOS350A – DECEMBER 2006 – REVISED MAY 2008

The dc gain for this circuit is equal to RF. At high

frequencies,

the

DAC

output

capacitance

(CD)

produces a zero in the noise gain for the OPA4830

that may cause peaking in the closed-loop frequency

response. CF is added across RF to compensate for

Because

the

OPA4830

unity-gain

stable,

this

noise-gain

peaking.

achieve

flat

voltage-feedback op amp, a wide range of resistor

transimpedance frequency response, this pole in the

values may be used for the feedback and gain setting

feedback network should be set to:

resistors. The primary limits on these values are set

by dynamic range (noise and distortion) and parasitic

capacitance

considerations.

For

noninverting

unity-gain

follower

application,

the

feedback

which

gives

corner

frequency

f–3dB

connection should be made with a direct short.

approximately:

Below

200

Ω,

the

feedback

network

presents

additional output loading that can degrade the

harmonic distortion performance of the OPA4830.

Above

Ω,

the

typical

parasitic

capacitance

(approximately 0.2pF) across the feedback resistor

may cause unintentional band limiting in the amplifier

response.

A good rule of thumb is to target the parallel

A printed circuit board (PCB) is available to assist in

combination of RF and RG (see Figure 74) to be less

the initial evaluation of circuit performance using the

than about 400

Ω. The combined impedance RF || RG

OPA4830. The fixture is offered free of charge as

interacts with the inverting input capacitance, placing

unpopulated PCB, delivered with a user’s guide. The

an additional pole in the feedback network, and thus

summary information for this fixture is shown in

a zero in the forward response. Assuming a 2pF total

Table 2.

parasitic on the inverting node, holding RF || RG <

400

Ω keeps this pole above 200MHz. By itself, this

Table 2. Demonstration Fixture

constraint implies that the feedback resistor RF can

increase to several k

Ω at high gains. This increase is

LITERATURE

PRODUCT

PACKAGE

ORDERING NUMBER

NUMBER

acceptable as long as the pole formed by RF and any

OPA4830IPW

TSSOP-14

DEM-OPA-TSSOP-4A

SBOU017

parasitic capacitance appearing in parallel is kept out

of the frequency range of interest.

The demonstration fixture can be requested at the

In the inverting configuration, an additional design

Texas Instruments web site (www.ti.com) through the

consideration must be noted. RG becomes the input

OPA4830 product folder.

resistor and therefore the load impedance to the

driving source. If impedance matching is desired, RG

may be set equal to the required termination value.

SUPPORT

However,

low

inverting

gains,

the

resulting

Computer simulation of circuit performance using

feedback resistor value can present a significant load

SPICE

often

quick

way

analyze

the

to the amplifier output. For example, an inverting gain

performance of the OPA4830 and its circuit designs.

of 2 with a 50

Ω input matching resistor (= RG) would

This approach is particularly true for video and RF

require a 100

Ω feedback resistor, which would

amplifier circuits where parasitic capacitance and

contribute to output loading in parallel with the

inductance

can

play

major

role

circuit

external load. In such a case, it would be preferable

performance. A SPICE model for the OPA4830 is

to increase both the RF and RG values, and then

available through the TI web page (www.ti.com). Note

achieve the input matching impedance with a third

that this model is the OPA830 model applied to the

resistor to ground (see Figure 88). The total input

OPA4830 quad version. The applications department

impedance becomes the parallel combination of RG

is also available for design assistance. These models

and the additional shunt resistor.

predict typical small-signal ac, transient steps, dc

performance, and noise under a wide variety of

operating conditions. The models include the noise

terms found in the electrical specifications of the data

sheet. This model does not attempt to distinguish

between the package types in their small-signal ac

performance.

Submit Documentation Feedback

Product Folder Link(s): OPA4830

OPA690 Datasheet(PDF) 31 Page - Texas Instruments

OPA690 Datasheet(HTML) 31 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 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

Datasheet Download

Link URL