OPA2889 datasheet(16/38 Pages) NSC

16 / 38 page

APPLICATIONS INFORMATION

WIDEBAND VOLTAGE-FEEDBACK

1/2

OPA2889

+5V

-VS

DIS

-5V

Load

50W

350W

50W

Source

750W

6.8 F

0.1 F

6.8 F

0.1 F

OPA2889

SBOS373B – JUNE 2007 – REVISED AUGUST 2008 ....................................................................................................................................................... www.ti.com

OPERATION

The OPA2889 provides an exceptional combination

of high output power capability in a dual, wideband,

unity-gain stable, voltage-feedback op amp using a

new high slew rate input stage. Typical differential

input stages used for voltage-feedback op amps are

designed

steer

fixed-bias

current

the

compensation

capacitor,

setting

limit

the

achievable slew rate. The OPA2889 uses a new input

stage that places the transconductance element

between two input buffers, using the output currents

as the forward signal. As the error voltage increases

across the two inputs, an increasing current is

delivered

the

compensation

capacitor.

This

configuration provides high slew rate (250V/

µs) while

consuming very low quiescent current (460

µA/ch).

This exceptional full-power performance comes at the

price of a slightly higher input noise voltage than

alternative architectures. The 8.4nV/

√Hz input voltage

noise for the OPA2889 is exceptionally low for this

Figure 50. DC-Coupled, G = +2, Bipolar Supply,

type of input stage.

Specification and Test Circuit

Figure 50 shows the dc-coupled, gain of +2V/V, dual

power-supply circuit configuration used as the basis

Figure 51 illustrates the ac-coupled, gain of +2V/V,

of the ±5V Electrical Characteristics and ±5V Typical

single-supply circuit configuration used as the basis

Chararacteristics. This illustration is for one channel;

of the +5V Electrical Characteristics and +5V Typical

the other channel is connected similarly. For test

Chararacteristics. Though not a rail-to-rail design, the

purposes, the input impedance is set to 50

Ω with a

OPA2889 requires minimal input and output voltage

resistor to ground and the output impedance is set to

headroom

compared

other

very

wideband

100

Ω. Voltage swings reported in the Electrical

voltage-feedback op amps. It delivers a 2.8VPP output

Characteristics are taken directly at the input and

swing on a single +5V supply with > 50MHz

output pins, while output powers (dBm) are at the

bandwidth.

The

key

requirement

broadband

matched 50

Ω load. For the circuit of Figure 50, the

single-supply operation is to maintain input and

total effective load will be 100

Ω || 1.5kΩ. The disable

output signal swings within the usable voltage ranges

control line (MSOP-10 package only) is typically left

at both the input and the output. The circuit of

open for normal amplifier operation. Two optional

Figure 51 establishes an input midpoint bias using a

components are included in Figure 50. An additional

simple resistive divider from the +5V supply (two

resistor

(350

Ω) is

included

series

with

the

698

Ω resistors). Separate bias networks would be

noninverting input. Combined with the 25

Ω dc source

required at each input. The input signal is then

resistance looking back towards the signal generator,

ac-coupled into the midpoint voltage bias. The input

this resistor gives an input bias current cancelling

voltage can swing to within 1.1V of either supply pin,

resistance that matches the 375

Ω source resistance

giving a 2VPP input signal range centered between

seen at the inverting input (see the DC Accuracy and

the supply pins. The input impedance matching

Offset Control section). In addition to the usual

resistor (59

Ω) used for testing is adjusted to give a

power-supply decoupling capacitors to ground, a

Ω input load when the parallel combination of the

0.1

µF capacitor is included between the two

biasing divider network is included.

power-supply pins. In practical printed circuit board

(PCB) layouts, this optional-added capacitor typically

improves the 2nd-harmonic distortion performance by

3dB to 6dB.

Submit Documentation Feedback

Product Folder Link(s): OPA2889

OPA2889 Datasheet(PDF) 16 Page - National Semiconductor (TI)

OPA2889 Datasheet(HTML) 16 Page - National Semiconductor (TI)

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

Datasheet Download

Link URL