Datasheet

1/2
OPA2890
+5V
+V
S
-V
S
+
DIS
-5V
100 LoadW
50W
350W
100WV
O
V
D
V
I
50 SourceW
R
G
750W
R
F
750W
+
6.8 Fm
0.1 Fm 6.8 Fm
0.1 Fm
0.1 Fm
OPA2890
SBOS364C –DECEMBER 2007–REVISED DECEMBER 2009 www.ti.com
APPLICATIONS INFORMATION
WIDEBAND VOLTAGE-FEEDBACK
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 to steer a fixed-bias current to the
compensation capacitor, setting a limit to 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 to 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 50Ω with a
OPA2890 requires minimal input and output voltage
resistor to ground and the output impedance is set to
headroom compared to other very wideband
200Ω. Voltage swings reported in the Electrical
voltage-feedback op amps. It delivers a 3V
PP
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 of
matched 50Ω load. For the circuit of Figure 49, the
broadband single-supply operation is to maintain
total effective load is 200Ω || 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 (350Ω) is included in series with
(two 698Ω resistors). Separate bias networks would
the noninverting input. Combined with the 25Ω 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 750Ω source
giving a 2V
PP
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 (59Ω) used for testing is adjusted to give a
the usual power-supply decoupling capacitors to
50Ω input load when the parallel combination of the
ground, a 0.1μF 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.
16 Submit Documentation Feedback Copyright © 2007–2009, Texas Instruments Incorporated
Product Folder Link(s): OPA2890