OPA2832 datasheet(24/37 Pages) NSC

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DESIGN-IN TOOLS

DEMONSTRATION FIXTURES

DRIVING CAPACITIVE LOADS

MACROMODEL AND APPLICATIONS

OPERATING SUGGESTIONS

OUTPUT CURRENT AND VOLTAGES

OPA2832

SBOS327C – FEBRUARY 2005 – REVISED AUGUST 2008 ............................................................................................................................................. www.ti.com

the available output voltage and current will always

be greater than that shown in the over-temperature

specifications,

since

the

output

stage

junction

temperatures will be higher than the minimum

Two printed circuit boards (PCBs) are available to

specified operating ambient.

assist in the initial evaluation of circuit performance

using the OPA2832 in its two package options. Both

To maintain maximum output stage linearity, no

of these are offered free of charge as unpopulated

output short-circuit protection is provided. This will not

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

normally be a problem, since most applications

information for these fixtures is shown in Table 1.

include a series matching resistor at the output that

will limit the internal power dissipation if the output

Table 1. Demonstration Fixtures by Package

side of this resistor is shorted to ground. However,

shorting the output pin directly to the adjacent

ORDERING

LITERATURE

positive power-supply pin (8-pin packages) will, in

PRODUCT

PACKAGE

NUMBER

most cases, destroy the amplifier. If additional

OPA2832ID

SO-8

DEM-OPA-SO-2A

SBOU003

short-circuit protection is required, consider a small

OPA2832IDGK

MSOP-8

DEM-OPA-MSOP-2A

SBOU004

series resistor in the power-supply leads. This will

reduce the available output voltage swing under

The demonstration fixtures can be requested at the

heavy output loads.

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

OPA2832 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

ADC—including additional external capacitance which

SPICE

often

quick

way

analyze

the

may be recommended to improve ADC linearity. A

performance of the OPA2832 and its circuit designs.

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

This is particularly true for video and RF amplifier

OPA2832 can be very susceptible to decreased

circuits where parasitic capacitance and inductance

stability and closed-loop response peaking when a

can play a major role on circuit performance. A

capacitive load is placed directly on the output pin.

SPICE model for the OPA2832 is available through

When the primary considerations are frequency

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

response flatness, pulse response fidelity, and/or

department is also available for design assistance.

distortion, the simplest and most effective solution is

These models predict typical

small

signal

AC,

to isolate the capacitive load from the feedback loop

transient steps, DC performance, and noise under a

by inserting a series isolation resistor between the

wide variety of operating conditions. The models

amplifier output and the capacitive load.

include the noise terms found in the electrical

specifications of the data sheet. These models do not

The

Typical

Characteristic

curves

show

the

attempt to distinguish between the package types in

recommended RS versus capacitive load and the

their small-signal AC performance.

resulting frequency response at the load. Parasitic

capacitive loads greater than 2pF can begin to

degrade the performance of the OPA2832. Long PC

board traces, unmatched cables, and connections to

multiple devices can easily exceed this value. Always

consider

this

effect

carefully,

and

add

the

The OPA2832 provides outstanding output voltage

recommended series resistor as close as possible to

capability.

For

the

+5V

supply,

under

no-load

the output pin (see the Board Layout Guidelines

conditions at +25°C, the output voltage typically

section).

swings closer than 90mV to either supply rail.

The criterion for setting this RS resistor is a maximum

The minimum specified output voltage and current

bandwidth, flat frequency response at the load. For a

specifications over temperature are set by worst-case

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

simulations at the cold temperature extreme. Only at

is already slightly peaked without the capacitive load,

cold startup will the output current and voltage

requiring relatively high values of RS to flatten the

decrease to the numbers shown in the ensured

response at the load. Increasing the noise gain will

tables. As the output transistors deliver power, their

also reduce the peaking (see Figure 24).

junction temperatures will increase, decreasing their

VBEs (increasing the available output voltage swing)

and increasing their current gains (increasing the

available output current). In steady-state operation,

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