OPA1641 datasheet(13/22 Pages) TI

13 / 22 page

OPA164x

IfR >2k

orR ||R >2k

R =R ||R

VIN

VOUT

OPA1641

OPA1642

OPA1644

www.ti.com

SBOS484A – DECEMBER 2009 – REVISED APRIL 2010

SOURCE IMPEDANCE AND DISTORTION

PHASE-REVERSAL PROTECTION

For lowest distortion with a source or feedback

The OPA1641, OPA1642, and OPA1644 family has

network, the impedance seen by the positive and

internal phase-reversal protection. Many FET- and

negative inputs in noninverting applications should be

bipolar-input op amps exhibit a phase reversal when

matched. The n-channel JFETs in the FET input

the input is driven beyond its linear common-mode

stage exhibit a varying input capacitance with applied

range. This condition is most often encountered in

common-mode

input

voltage.

inverting

noninverting circuits when the input is driven beyond

configurations, the input does not vary with input

the specified common-mode voltage range, causing

voltage because the inverting input is held at virtual

the output to reverse into the opposite rail. The input

ground. However, in noninverting applications, the

circuitry of the OPA1641, OPA1642, and OPA1644

inputs do vary, and the gate-to-source voltage is not

prevents

phase

reversal

with

excessive

constant. This effect produces increased distortion as

common-mode voltage; instead, the output limits into

a result of the varying capacitance for unmatched

the appropriate rail (see Figure 14).

source impedances.

OUTPUT CURRENT LIMIT

To maintain low distortion, match unbalanced source

impedance with appropriate values in the feedback

The output current of the OPA164x series is limited

network as shown in Figure 34. Of course, the

internal

circuitry

+36mA/–30mA

unbalanced impedance may be from gain-setting

(sourcing/sinking), to protect the device if the output

resistors

the

feedback

path.

the

parallel

is accidentally shorted. This short-circuit current

combination of R1 and R2 is greater than 2kΩ, a

depends on temperature, as shown in Figure 28.

matching impedance on the noninverting input should

Although it is uncommon for most modern audio

be used. As always, resistor values should be

applications to require 600

Ω load drive capability,

minimized to reduce the effects of thermal noise.

many audio op amp applications continue to specify

the total harmonic distortion (THD+N) at 600

Ω load

for comparative purposes. Figure 7 and Figure 9

provide typical THD+N measurement curves for the

OPA164x series, where the output drives a 3VRMS

signal into a 600

Ω load. However, it should be noted

that correct device operation cannot be ensured when

driving 600

Ω loads at full supply. Depending on

supply voltage and temperature, it may well trigger

the output current limit circuitry of the device.

POWER DISSIPATION AND THERMAL

Figure 34. Impedance Matching for Maintaining

PROTECTION

Low Distortion in Noninverting Circuits

The OPA164x series of op amps are capable of

driving 2k

Ω loads with power-supply voltages of up to

±18V over the specified temperature range. In a

CAPACITIVE LOAD AND STABILITY

single-supply

configuration,

where

the

load

The dynamic characteristics of the OPA164x have

connected

the

negative

supply

voltage,

the

been optimized for commonly encountered gains,

minimum load resistance is 2.8k

Ω at a supply voltage

loads, and operating conditions. The combination of

+36V.

For

lower

supply

voltages

(either

low closed-loop gain and high capacitive loads

single-supply or symmetrical supplies), a lower load

decreases the phase margin of the amplifier and can

resistance may be used, as long as the output current

lead to gain peaking or oscillations. As a result,

does not exceed 13mA; otherwise, the device

heavier capacitive loads must be isolated from the

short-circuit current protection circuit may activate.

output. The simplest way to achieve this isolation is to

Internal power dissipation increases when operating

add a small resistor (ROUT equal to 50Ω, for example)

high

supply

voltages.

Copper

leadframe

in series with the output.

construction used in the OPA1641, OPA1642, and

Figure

and

Figure

illustrate

graphs

OPA1644 series devices improves heat dissipation

Small-Signal

Overshoot

Capacitive

Load

for

compared to conventional materials. PCB layout can

several values of ROUT. Also, refer to Applications

also help reduce a possible increase in junction

Bulletin

AB-028

(literature

number

SBOA015,

available for download from the TI web site) for

details of analysis techniques and application circuits.

Product Folder Link(s): OPA1641 OPA1642 OPA1644

OPA1641 Datasheet(PDF) 13 Page - Texas Instruments

OPA1641 Datasheet(HTML) 13 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

Datasheet Download

Link URL