OPA2674 Datasheet, PDF (16/33 Pages) Burr-Brown (TI) – Dual Wideband, High Output Current Operational Amplifier with Current Limit

OPA2674
SBOS270A − AUGUST 2003 − REVISED MAY 2006
APPLICATION INFORMATION
WIDEBAND CURRENT-FEEDBACK OPERATION
The OPA2674 gives the exceptional AC performance of a
wideband current-feedback op amp with a highly linear,
high-power output stage. Requiring only 9mA/ch
quiescent current, the OPA2674 swings to within 1V of
either supply rail and delivers in excess of 380mA at room
temperature. This low output headroom requirement,
along with supply voltage independent biasing, gives
remarkable single (+5V) supply operation. The OPA2674
delivers greater than 150MHz bandwidth driving a 2V_PP
output into 100Ω on a single +5V supply. Previous boosted
output stage amplifiers typically suffer from very poor
crossover distortion as the output current goes through
zero. The OPA2674 achieves a comparable power gain
with much better linearity. The primary advantage of a
current-feedback op amp over a voltage-feedback op amp
is that AC performance (bandwidth and distortion) is
relatively independent of signal gain. Figure 1 shows the
DC-coupled, gain of +4, dual power-supply circuit
configuration used as the basis of the ±6V Electrical 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 whereas load powers (dBm) are defined at a matched
50Ω load. For the circuit of Figure 1, the total effective load
is 100Ω || 535Ω = 84Ω.
+6V
0.1µF
+V_S
6.8µF
+
50Ω Source
V_I
50Ω
1/2
OPA2674
50Ω Load
V_O 50Ω
R_F
402Ω
R_G
133Ω
−V_S
−6V
6.8µF
0.1µF
Figure 1. DC-Coupled, G = +4, Bipolar Supply,
Specification and Test Circuit
16
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Figure 2 shows the DC-coupled, bipolar supply circuit
inverting gain configuration used as the basis for the ±6V
Electrical and Typical Characteristics. Key design
considerations of the inverting configuration are
developed in the Inverting Amplifier Operation discussion.
+6V _{Power−supply}
decoupling
not shown.
1/2
V_O
OPA2674
50Ω Load
50Ω
50Ω
Source
V_I
R_G
100Ω
R_M
100Ω
−6V _RF
402Ω
Figure 2. DC-Coupled, G = −4, Bipolar Supply,
Specification and Test Circuit
Figure 3 shows the AC-coupled, gain of +4, single-supply
circuit configuration used as the basis of the +5V Electrical
and Typical Characteristics. Though not a rail-to-rail
design, the OPA2674 requires minimal input and output
voltage headroom compared to other wideband
current-feedback op amps. It will deliver a 3V_PP output
swing on a single +5V supply with greater than 100MHz
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 3 establishes an input
midpoint bias using a simple resistive divider from the +5V
supply (two 806Ω resistors). The input signal is then
AC-coupled into this midpoint voltage bias. The input
voltage can swing to within 1.3V of either supply pin, giving
a 2.4V_PP input signal range centered between the supply
pins. The input impedance matching resistor (57.6Ω) used
for testing is adjusted to give a 50Ω input match when the
parallel combination of the biasing divider network is
included. The gain resistor (R_G) is AC-coupled, giving the
circuit a DC gain of +1which puts the input DC bias
voltage (2.5V) on the output as well. The feedback resistor
value is adjusted from the bipolar supply condition to
re-optimize for a flat frequency response in +5V, gain of +4,
operation. Again, on a single +5V supply, the output
voltage can swing to within 1V of either supply pin while
delivering more than 200mA output current. A demanding
100Ω load to a midpoint bias is used in this
characterization circuit. The new output stage used in the
OPA2674 can deliver large bipolar output currents into this
midpoint load with minimal crossover distortion, as shown
by the +5V supply, harmonic distortion plots in the Typical
Characteristics charts.