Datasheet

I =
RG
V
OUT
A R´
V
MAX G
VCA820
SBOS395C –OCTOBER 2007–REVISED OCTOBER 2009............................................................................................................................................ www.ti.com
MAXIMUM GAIN OF OPERATION OUTPUT CURRENT AND VOLTAGE
This section describes the use of the VCA820 in a The VCA820 provides output voltage and current
fixed-gain application in which the V
G
control pin is capabilities that are unsurpassed in a low-cost
set at V
G
= +2V. The tradeoffs described here are monolithic VCA. Under no-load conditions at +25°C,
with bandwidth, gain, and output voltage range. the output voltage typically swings closer than 1V to
either supply rails; the +25°C swing limit is within
1.2V of either rails. Into a 15Ω load (the minimum
tested load), it is tested to deliver more than ±160mA.
In the case of an application that does not make use
of the V
GAIN
, but requires some other characteristic of
The specifications described above, though familiar in
the VCA820, the R
G
resistor must be set such that
the industry, consider voltage and current limits
the maximum current flowing through the resistance
separately. In many applications, it is the voltage ×
I
RG
is less than ±2.6mA typical, or 5.2mA
PP
as
current, or V-I product, that is more relevant to circuit
defined in the Electrical Characteristics table, and
operation. Refer to the Output Voltage and Current
must follow Equation 2.
Limitations plot (Figure 50) in the Typical
Characteristics. The X- and Y-axes of this graph
show the zero-voltage output current limit and the
(2)
zero-current output voltage limit, respectively. The
four quadrants give a more detailed view of the
As illustrated in Equation 2, once the output dynamic
VCA820 output drive capabilities, noting that the
range and maximum gain are defined, the gain
graph is bounded by a Safe Operating Area of 1W
resistor is set. This gain setting in turn affects the
maximum internal power dissipation. Superimposing
bandwidth, because in order to achieve the gain (and
resistor load lines onto the plot shows that the
with a set gain element), the feedback element of the
VCA820 can drive ±2.5V into 25Ω or ±3.5V into 50Ω
output stage amplifier is set as well. Keeping in mind
without exceeding the output capabilities or the 1W
that the output amplifier of the VCA820 is a
dissipation limit. A 100Ω load line (the standard test
current-feedback amplifier, the larger the feedback
circuit load) shows the full ±3.9V output swing
element, the lower the bandwidth as the feedback
capability, as shown in the Typical Characteristics.
resistor is the compensation element.
Limiting the discussion to the input voltage only and
ignoring the output voltage and gain, Figure 3
illustrates the tradeoff between the input voltage and
the current flowing through the gain resistor.
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