OPA690 datasheet(16/35 Pages) TI

16 / 35 page

www.ti.com

APPLICATIONS INFORMATION

WIDEBAND VOLTAGE-FEEDBACK

1/2

OPA2890

+5V

-VS

DIS

-5V

100

Load

50W

350W

100W

Source

750W

6.8 F

0.1 F

6.8 F

0.1 F

OPA2890

SBOS364A – DECEMBER 2007 – REVISED DECEMBER 2007

OPERATION

The OPA2890 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 OPA2890 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 (400V/

µs) while

consuming

relatively

low

quiescent

current

(1.12mA/ch). This exceptional full-power performance

comes at the price of a slightly higher input noise

voltage than alternative architectures; however, the

8nV/

√Hz input voltage noise for the OPA2890 is

Figure 49. DC-Coupled, G = +2V/V, Bipolar

exceptionally low for this type of input stage.

Supply, Specification and Test Circuit

Figure 49 shows the DC-coupled, gain of +2V/V, dual

power-supply circuit configuration used as the basis

Figure 50 illustrates the ac-coupled, gain of +2V/V,

of the ±5V Electrical Characteristics and Typical

single-supply circuit configuration used as the basis

Characteristics. This illustration is for one channel;

of the +5V Electrical Characteristics and Typical

the other channel is connected similarly. For test

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

purposes, the input impedance is set to 50

Ω with a

OPA2890 requires minimal input and output voltage

resistor to ground and the output impedance is set to

headroom

compared

other

very

wideband

200

Ω. Voltage swings reported in the Electrical

voltage-feedback op amps. It delivers a 3VPP output

Characteristics are taken directly at the input and

swing on a single +5V supply with greater than

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

80MHz

bandwidth.

The

key

requirement

matched 50

Ω load. For the circuit of Figure 49, the

broadband single-supply operation is to maintain

total effective load is 200

Ω || 1.5kΩ. The disable

input and output signal swings within the usable

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

voltage ranges at both the input and the output. The

open for normal amplifier operation. Two optional

circuit of Figure 50 establishes an input midpoint bias

components are included in Figure 49. First, an

using a simple resistive divider from the +5V supply

additional resistor (350

Ω) is included in series with

(two 698

Ω resistors). Separate bias networks would

the noninverting input. Combined with the 25

Ω dc

be required at each input. The input signal is then

source resistance looking back towards the signal

ac-coupled into the midpoint voltage bias. The input

generator, this resistor gives an input bias current

voltage can swing to within 1.5V of either supply pin,

cancelling resistance that matches the 750

Ω source

giving a 2VPP input signal range centered between

resistance seen at the inverting input (see the DC

the supply pins. The input impedance matching

Accuracy and Offset Control section). In addition to

resistor (59

Ω) used for testing is adjusted to give a

the usual power-supply decoupling capacitors to

Ω input load when the parallel combination of the

ground, a 0.1

µF capacitor is also included between

biasing divider network is included.

the two power-supply pins. In practical printed circuit

board (PCB) layouts, this optional capacitor typically

improves the 2nd-harmonic distortion performance by

3dB to 6dB.

Submit Documentation Feedback

Product Folder Link(s): OPA2890

OPA690 Datasheet(PDF) 16 Page - Texas Instruments

OPA690 Datasheet(HTML) 16 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

Datasheet Download

Link URL