Datasheet

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