Datasheet
*
*
e
nOUTPUT
i
niOUTPUT
i
inOUTPUT
I
CORE
e
nINPUT
i
nINPUT
R
F
4kTR
F
*
R
S2
4kTR
S2
*
R
F
4kTR
F
e
O
FB
GND
V
OUT
V
REF
V
G
V
G
x1
*
e
nINPUT
i
nINPUT
*
x1
R
G
(Noiseless)
+R
G
-R
G
V-
-V
IN
+V
IN
*
R
S1
4kTR
S1
i
nINPUT
V+
T =T +P ´ q
J D JA
A
P =10V(38mA)+5 /(4 100 )=442.5mW´ W
D
2
MaximumT =+85 C+(0.449W 80 C/W)=120.5 C° ´ ° °
J
VCA820
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............................................................................................................................................ SBOS395C –OCTOBER 2007–REVISED OCTOBER 2009
Figure 89. Full Noise Model
however, it is at a maximum when the output is fixed
THERMAL ANALYSIS
at a voltage equal to one-half of either supply voltage
(for equal bipolar supplies). Under this worst-case
The VCA820 does not require heatsinking or airflow
condition, P
DL
= V
S
2
/(4 × R
L
), where R
L
is the
in most applications. The maximum desired junction
resistive load.
temperature sets the maximum allowed internal
power dissipation as described in this section. In no
Note that it is the power in the output stage and not in
case should the maximum junction temperature be
the load that determines internal power dissipation.
allowed to exceed +150°C.
As a worst-case example, compute the maximum T
J
using a VCA820ID (SO-14 package) in the circuit of
Operating junction temperature (T
J
) is given by
Figure 76 operating at maximum gain and at the
Equation 6:
maximum specified ambient temperature of +85°C.
(6)
(7)
The total internal power dissipation (P
D
) is the sum of
quiescent power (P
DQ
) and additional power
(8)
dissipated in the output stage (P
DL
) to deliver load
power. Quiescent power is simply the specified
This maximum operating junction temperature is well
no-load supply current times the total supply voltage
below most system level targets. Most applications
across the part. P
DL
depends on the required output
should be lower because an absolute worst-case
signal and load; for a grounded resistive load,
output stage power was assumed in this calculation
of V
CC
/2, which is beyond the output voltage range for
the VCA820.
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