OPA3695_14 Datasheet, PDF (17/39 Pages) Texas Instruments – Triple, Ultra-Wideband, Current-Feedback OPERATIONAL AMPLIFIER with Disable

OPA3695
www.ti.com ............................................................................................................................................... SBOS355A – APRIL 2008 – REVISED SEPTEMBER 2008
DESIGN-IN TOOLS
DEMONSTRATION BOARDS
A printed circuit board (PCB) is available to assist in
the initial evaluation of circuit performance using the
OPA3695. The fixture is offered free of charge as an
unpopulated PCB, delivered with a user's guide. The
summary information for this fixture is shown in
Table 1.
Table 1. Demonstration Fixture
PRODUCT
OPA3695IDBQ,
noninverting
OPA3695IDBQ,
inverting
PACKAGE
SSOP-16
SSOP-16
ORDERING
NUMBER
DEM-OPA-SSOP-3C
DEM-OPA-SSOP-3D
LITERATURE
NUMBER
SBOU047
SBOU046
The demonstration fixture can be requested at the
Texas Instruments web site (www.ti.com) through the
OPA3695 product folder.
OPERATING SUGGESTIONS
GAIN SETTING
Similar to other current-feedback amplifiers, the
OPA3695 compensation is dictated by the feedback
resistor—R_F. As the resistance increases, more
compensation is added to the amplifier. It is important
to realize that increasing the resistance too far is not
recommended because this increase causes a zero
to form on the inverting input as a result of stray
capacitance. In general, R_F should not exceed 1.5kΩ
to 2kΩ, or else stability is a concern. Table 2 shows
the recommended feedback values for common gain
settings. These values are a good starting point; fine
tuning of the resistor value(s) should be done to
account for individual PCB designs and other factors.
Table 2. Recommended Feedback Resistor—R_F
GAIN (V/V)
±5V OR 10V
SUPPLY
±2.5V OR 5V
SUPPLY
+1
909Ω
750Ω
+2, –1
604Ω
499Ω
+4
511Ω
453Ω
+8
402Ω
348Ω
+16
249Ω
162Ω
OUTPUT CURRENT AND VOLTAGE
The OPA3695 provides output voltage and current
capabilities that can easily support multiple video
loads and/or 100Ω loads with very low distortion.
Under no-load conditions at +25°C, the output voltage
typically swings to 1V of either supply rail. Into a 15Ω
load (the minimum tested load), it is tested to deliver
±120mA.
The specifications described above, though familiar in
the industry, consider voltage and current limits
separately. In many applications, it is the voltage ×
current, or V-I product, which is more relevant to
circuit operation. Refer to the Output Voltage and
Current Limitations plot (Figure 18) in the Typical
Characteristics. The X- and Y-axes of this graph
show the zero-voltage output current limit and the
zero-current output voltage limit, respectively. The
four quadrants give a more detailed view of the
OPA3695 output drive capabilities, noting that the
graph is bounded by a Safe Operating Area of 1W
maximum internal power dissipation. Superimposing
resistor load lines onto the plot shows that the
OPA3695 can drive ±3.4V into 20Ω or ±3.7V into 50Ω
without exceeding either the output capabilities or the
1W dissipation limit. A 100Ω load line (the standard
test-circuit load) shows full ±3.8V output swing
capability, as shown in the Typical Characteristics.
The minimum specified output voltage and current
specifications over temperature are set by worst-case
simulations at the cold temperature extreme. Only at
cold startup do the output current and voltage
decrease to the numbers shown in the
over-temperature min/max specifications. As the
output transistors deliver power, the junction
temperatures increase, which decreases the V_BEs
(increasing the available output voltage swing) and
increases the current gains (increasing the available
output current). In steady-state operation, the
available output voltage and current are always
greater than that shown in the over-temperature
characteristics since the output stage junction
temperatures are higher than the minimum specified
operating ambient.
To maintain maximum output stage linearity, no
output short-circuit protection is provided. This
configuration is not normally a problem, because
most applications include a series matching resistor
at the output that limits the internal power dissipation
if the output side of this resistor is shorted to ground.
However, shorting the output pin directly to an
adjacent positive power-supply pin, in most cases,
destroys the amplifier. If additional protection to a
power-supply short is required, consider a small
series resistor in the power-supply leads. Under
heavy output loads, this resistor reduces the available
output voltage swing. A 5Ω series resistor in each
supply lead, for example, limits the internal power
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): OPA3695
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