OPA690IDBVT datasheet(14/37 Pages) TI1

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OPA690

+5V

DIS

-5V

Load

50W

Source

402W

6.8 F

0.1 F

6.8 F

0.1 F

175W

OPA690

+5V

DIS

S/2

698W

100W

50W

59W

698W

0.1 F

6.8 F

0.1 F

402W

Source

OPA690

SBOS223F – DECEMBER 2001 – REVISED FEBRUARY 2010

www.ti.com

APPLICATION INFORMATION

WIDEBAND VOLTAGE-FEEDBACK

bandwidth.

The

key

requirement

broadband

OPERATION

single-supply operation is to maintain input and

output signal swings within the useable voltage

The OPA690 provides an exceptional combination of

ranges at both the input and the output. The circuit of

high output power capability with a wideband,

Figure 37 establishes an input midpoint bias using a

unity-gain stable voltage-feedback op amp using a

simple resistive divider from the +5V supply (two

new high slew rate input stage. Typical differential

698

Ω resistors). The input signal is then ac-coupled

input stages used for voltage feedback op amps are

into the midpoint voltage bias. The input voltage can

designed

steer

fixed-bias

current

the

swing to within 1.5V of either supply pin, giving a

compensation

capacitor,

setting

limit

the

2VPP input signal range centered between the supply

achievable slew rate. The OPA690 uses a new input

pins. The input impedance matching resistor (59

Ω)

stage which places the transconductance element

used for testing is adjusted to give a 50

Ω input load

between two input buffers, using their output currents

when the parallel combination of the biasing divider

as the forward signal. As the error voltage increases

network is included.

across the two inputs, an increasing current is

delivered

the

compensation

capacitor.

This

provides very high slew rate (1800V/ms) while

consuming relatively low quiescent current (5.5mA).

This exceptional full-power performance comes at the

price of a slightly higher input noise voltage than

alternative architectures. The 5.5nV/

√Hz input voltage

noise for the OPA690 is exceptionally low for this

type of input stage.

Figure 36 shows the dc-coupled, gain of +2, dual

power supply circuit configuration used as the basis

of the ±5V Electrical Characteristics and Typical

Characteristics.

For

test

purposes,

the

input

impedance is set to 50

Ω with a resistor to ground and

the output impedance is set to 50

Ω with a series

output resistor. Voltage swings reported in the

specifications are taken directly at the input and

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

matched 50

Ω load. For the circuit of Figure 36, the

Figure 36. DC-Coupled, G = +2, Bipolar-Supply

total effective load will be 100

Ω || 804Ω. The disable

Specification and Test Circuit

control line is typically left open to ensure normal

amplifier operation. Two optional components are

included in Figure 36. An additional resistor (175

Ω) is

included

series

with

the

noninverting

input.

Combined with the 25

Ω dc source resistance looking

back towards the signal generator, this gives an input

bias current cancelling resistance that matches the

200

Ω source resistance seen at the inverting input

(see the DC Accuracy and Offset Control section). In

addition

the

usual

power-supply

decoupling

capacitors to ground, a 0.1mF capacitor is included

between the two power-supply pins. In practical

printed

circuit

board

(PCB)

layouts,

this

optional-added capacitor will typically improve the

2nd-harmonic distortion performance by 3dB to 6dB.

Figure

37 shows

the

ac-coupled,

gain

+2,

single-supply circuit configuration which is the basis

of the +5V Electrical Characteristics and Typical

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

OPA690 requires minimal input and output voltage

headroom

compared

other

very

wideband

Figure 37. AC-Coupled, G = +2, Single-Supply

voltage-feedback op amps. It will deliver a 3VPP

Specification and Test Circuit

output swing on a single +5V supply with > 150MHz

Product Folder Link(s): OPA690

OPA690IDBVT Datasheet(PDF) 14 Page - Texas Instruments

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