OPA3693 Datasheet, PDF (21/29 Pages) Burr-Brown (TI) – Triple, Ultra-Wideband, Fixed-Gain, VIDEO BUFFER with Disable

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DESIGN-IN TOOLS
DEMONSTRATION BOARDS
A printed circuit board (PCB) is available to assist in
the initial evaluation of circuit performance using the
OPA3693. 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 2.
Table 2. Demonstration Fixture
PRODUCT
OPA3693IDBQ,
Noninverting
OPA3693IDBQ,
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
OPA3693 product folder.
OPERATING SUGGESTIONS
GAIN SETTING
Setting the gain for the OPA3693 is very easy. For a
gain of +2, ground the –IN pin and drive the +IN pin
with the signal. For a gain of +1, either leave the –IN
pin open and drive the +IN pin or drive both the +IN
and –IN pins (see Figure 47). For a gain of –1,
ground the +IN pin and drive the –IN pin with the
input signal. An external resistor may be used in
series with the –IN pin to reduce the gain. However,
because the internal resistors (R_F and R_G) have a
tolerance and temperature drift different than the
external resistor, the absolute gain accuracy and
gain drift over temperature are relatively poor
compared to the previously described standard gain
connections using no external resistor.
OUTPUT CURRENT AND VOLTAGE
The OPA3693 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;
the tested swing limit is within 1.2V of either rail. Into
a 15Ω load (the minimum tested load), it is tested to
deliver more than ±90mA.
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 21) in the Typical
Characteristics. The X- and Y-axes of this graph
OPA3693
SBOS353 – DECEMBER 2006
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
OPA3693 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
OPA3693 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 will the output current
and voltage decrease to the numbers shown in the
over-temperature min/max specifications. As the
output transistors deliver power, their junction
temperatures increase, which decreases their V_BEs
(increasing the available output voltage swing) and
increases their current gains (increasing the
available output current). In steady-state operation,
the available output voltage and current is 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, since 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 reduces the available output
voltage swing. A 5Ω series resistor in each supply
lead limits the internal power dissipation to < 1W for
an output short while decreasing the available output
voltage swing only 0.5V, for up to 100mA desired
load currents. Always place the 0.1µF power-supply
decoupling capacitors after these supply-current
limiting resistors directly on the device supply pins.
DRIVING CAPACITIVE LOADS
One of the most demanding, and yet very common,
load conditions for an op amp is capacitive loading.
Often, the capacitive load is the input of an
analog-to-digital converter (ADC), including
additional external capacitance, which may be
recommended to improve ADC linearity. A
high-speed, high open-loop gain amplifier like the
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