Datasheet

OPA690
+5V
+
DIS
-5V
50 LoadW
50W
50WV
O
V
I
50 SourceW
R
G
402W
R
F
402W
+
6.8 Fm
0.1 Fm 6.8 Fm
0.1 Fm
0.1 Fm
175W
OPA690
+5V
+V
S
DIS
V
S
/2
698W
100WV
O
V
I
50W
59W
698W
0.1 Fm
0.1 Fm
+
6.8 Fm0.1 Fm
R
G
402W
R
F
402W
50 SourceW
OPA690
SBOS223F –DECEMBER 2001–REVISED FEBRUARY 2010 www.ti.com
APPLICATION INFORMATION
WIDEBAND VOLTAGE-FEEDBACK bandwidth. The key requirement of 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
698Ω 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 to steer a fixed-bias current to the
swing to within 1.5V of either supply pin, giving a
compensation capacitor, setting a limit to the
2V
PP
input signal range centered between the supply
achievable slew rate. The OPA690 uses a new input
pins. The input impedance matching resistor (59Ω)
stage which places the transconductance element
used for testing is adjusted to give a 50Ω 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 to 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 50Ω with a resistor to ground and
the output impedance is set to 50Ω 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 50Ω load. For the circuit of Figure 36, the
Figure 36. DC-Coupled, G = +2, Bipolar-Supply
total effective load will be 100Ω || 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 (175Ω) is
included in series with the noninverting input.
Combined with the 25Ω dc source resistance looking
back towards the signal generator, this gives an input
bias current cancelling resistance that matches the
200Ω source resistance seen at the inverting input
(see the DC Accuracy and Offset Control section). In
addition to 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 of +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 to other very wideband
Figure 37. AC-Coupled, G = +2, Single-Supply
voltage-feedback op amps. It will deliver a 3V
PP
Specification and Test Circuit
output swing on a single +5V supply with > 150MHz
14 Copyright © 2001–2010, Texas Instruments Incorporated
Product Folder Link(s): OPA690