OPA3690ID Datasheet, PDF (14/39 Pages) Texas Instruments – Triple, Wideband, Voltage-Feedback OPERATIONAL AMPLIFIER with Disable

OPA3690
SBOS237G – MARCH 2002 – REVISED MARCH 2010
www.ti.com
APPLICATION INFORMATION
WIDEBAND VOLTAGE-FEEDBACK
OPERATION
The OPA3690 provides an exceptional combination
of high output power capability in a 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 OPA3690 uses a new input
stage that places the transconductance element
between two input buffers, using their 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
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 OPA3690 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
Electrical Characteristics 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 total effective load will be 100Ω || 804Ω. The
disable control line is typically left open for normal
amplifier operation. Two optional components are
included in Figure 36. An additional resistor (100Ω) 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
125Ω 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.
bandwidth. The key requirement of broadband
single-supply operation is to maintain input and
output signal swings within the usable voltage ranges
at both the input and the output. The circuit of
Figure 37 establishes an input midpoint bias using a
simple resistive divider from the +5V supply (two
698Ω resistors). The input signal is then ac-coupled
into the midpoint voltage bias. The input voltage can
swing to within 1.5V of either supply pin, giving a
2V_PP input signal range centered between the supply
pins. The input impedance matching resistor (59Ω)
used for testing is adjusted to give a 50Ω input load
when the parallel combination of the biasing divider
network is included.
+5V
+V_S
0.1mF
6.8mF
+
50W Source
175W
V_I
50W
1/3
OPA3690
DIS
V_O 50W
50W Load
0.1mF
R_F
402W
R_G
402W
-V_S
-5V
6.8mF
0.1mF
Figure 36. DC-Coupled, G = +2, Bipolar-Supply
Specification and Test Circuit
+5V
+V_S
0.1mF
698W
50W
0.1mF
6.8mF
DIS
V_I
59W
698W
1/3
OPA3690
V_O 100W
V_S/2
R_F
402W
Figure 37 shows the ac-coupled, gain of +2,
single-supply circuit configuration used as the basis
of the +5V Electrical Characteristics and Typical
Characteristics. Though not a rail-to-rail design, the
OPA3690 requires minimal input and output voltage
headroom compared to other very wideband
voltage-feedback op amps. It will deliver a 3V_PP
output swing on a single +5V supply with > 150MHz
R_G
402W
0.1mF
Figure 37. AC-Coupled, G = +2, Single-Supply
Specification and Test Circuit
14
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