OPA2832 datasheet(23/32 Pages) BURR-BROWN

23 / 32 page

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DESIGN-IN TOOLS

DEMONSTRATION FIXTURES

DRIVING CAPACITIVE LOADS

MACROMODEL AND APPLICATIONS

OPERATING SUGGESTIONS

OUTPUT CURRENT AND VOLTAGES

OPA3832

SBOS370 – DECEMBER 2006

steady-state operation, the available output voltage

and current will always be greater than that shown in

the over-temperature specifications, because the

output stage junction temperatures will be higher

Two printed circuit boards (PCBs) are available to

than the minimum specified operating ambient.

assist in the initial evaluation of circuit performance

To maintain maximum output stage linearity, no

using the OPA3832 in its two package options. Both

output

short-circuit

protection

provided.

This

of these are offered free of charge as unpopulated

configuration will not normally be a problem, since

PCBs, delivered with a user's guide. The summary

most applications include a series matching resistor

information for these fixtures is shown in Table 1.

at the output that will limit the internal power

dissipation if the output side of this resistor is shorted

Table 1. Demonstration Fixtures by Package

to ground. However, shorting the output pin directly

ORDERING

LITERATURE

to the adjacent positive power-supply pin (8-pin

PRODUCT

PACKAGE

NUMBER

packages) will, in most cases, destroy the amplifier.

OPA3832ID

SO-14

DEM-OPA-SO-3B

SBOU018

additional

short-circuit

protection

required,

OPA3832IPW

TSSOP-14

DEM-OPA-SSOP-3B

SBOU019

consider a small series resistor in the power-supply

leads. This resistor will reduce the available output

The demonstration fixtures can be requested at the

voltage swing under heavy output loads.

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

OPA3832 product folder.

One of the most demanding and yet very common

SUPPORT

load conditions for an op amp is capacitive loading.

Often, the capacitive load is the input of an

Computer simulation of circuit performance using

Analog-to-Digital

Converter

(ADC)—including

SPICE

often

quick

way

analyze

the

additional

external

capacitance

which

may

performance of the OPA3832 and its circuit designs.

recommended

improve

ADC

linearity.

This is particularly true for video and RF amplifier

high-speed, high open-loop gain amplifier like the

circuits where parasitic capacitance and inductance

OPA3832 can be very susceptible to decreased

can play a major role on circuit performance. A

stability and closed-loop response peaking when a

SPICE model for the OPA3832 is available through

capacitive load is placed directly on the output pin.

the TI web page (www.ti.com). The applications

When the primary considerations are frequency

department is also available for design assistance.

response flatness, pulse response fidelity, and/or

These

models

predict

typical

small

signal

ac,

distortion, the simplest and most effective solution is

transient steps, dc performance, and noise under a

to isolate the capacitive load from the feedback loop

wide variety of operating conditions. The models

by inserting a series isolation resistor between the

include the noise terms found in the electrical

amplifier output and the capacitive load.

specifications of the data sheet. These models do

not attempt to distinguish between the package types

The

Typical

Characteristic

curves

show

the

in their small-signal ac performance.

recommended RS versus capacitive load and the

resulting frequency response at the load. Parasitic

capacitive loads greater than 2pF can begin to

degrade the performance of the OPA3832. Long

PCB traces, unmatched cables, and connections to

multiple devices can easily exceed this value. Always

The OPA3832 provides outstanding output voltage

consider

this

effect

carefully,

and

add

the

capability. For the +5V supply, under

no-load

recommended series resistor as close as possible to

conditions at +25

°C, the output voltage typically

the output pin (see the Board Layout Guidelines

swings closer than 90mV to either supply rail.

section).

The minimum specified output voltage and current

The criterion for setting this RS resistor is a maximum

specifications

over

temperature

are

set

bandwidth, flat frequency response at the load. For a

worst-case simulations at the cold temperature

gain of +2, the frequency response at the output pin

extreme. Only at cold startup will the output current

is already slightly peaked without the capacitive load,

and voltage decrease to the numbers shown in the

requiring relatively high values of RS to flatten the

ensured tables. As the output transistors deliver

response at the load. Increasing the noise gain will

power, the junction temperatures will increase,

also reduce the peaking.

decreasing the VBEs (increasing the available output

voltage swing) and increasing the current gains

(increasing

the

available

output

current).

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