Data Sheet
The effective load resistor (Rload ) will need to include
the effect of the feedback network. For instance,
eff
2
2
R
R
R
R
2
2
2
2
2
2
f
f
f
e = e 1+
+ in R
1+
+ i R
i
o
n
s
Rload in figure 3 would be calculated as:
eff
g
g
op amp noise terms e , i and i
R || (R + R )
n
n
i
L
f
g
2
2
These measurements are basic and are relatively easy to
perform with standard lab equipment. For design purposes
however, prior knowledge of actual signal levels and load
impedance is needed to determine the dissipated power.
Rf
Rf
+ eR2s 1 +
+ e2Rg
+ e2Rf
Rg
Rg
external resistor noise terms for R , R and R
f
S
g
Here, P can be found from
D
P = P
+ P
- P
D
Quiescent
Dynamic Load
High source impedances are sometimes unavoidable, but
they increase noise from the source impedance and also
make the circuit more sensitive to the op amp current
noise. Analyze all noise sources in the circuit, not just the
op amp itself, to achieve low noise in your application.
Quiescent power can be derived from the specified I val-
S
ues along with known supply voltage, V
. Load power
Supply
can be calculated as above with the desired signal ampli-
tudes using:
(V
)
= V
/ √2
LOAD RMS
PEAK
Power Dissipation
( I
)
= ( V
)
/ Rload
LOAD RMS
LOAD RMS eff
Power dissipation should not be a factor when operat-
ing under the stated 500Ω load condition. However, ap-
plications with low impedance, DC coupled loads should
be analyzed to ensure that maximum allowed junction
temperature is not exceeded. Guidelines listed below can
be used to verify that the particular application will not
cause the device to operate beyond it’s intended operat-
ing range.
The dynamic power is focused primarily within the output
stage driving the load. This value can be calculated as:
P
= (V - V
)
× ( I )
LOAD RMS
DYNAMIC
S+
LOAD RMS
Assuming the load is referenced in the middle of the pow-
er rails or V /2.
supply
Maximum power levels are set by the absolute maximum
junction rating of 150°C. To calculate the junction tem-
Figure 4 shows the maximum safe power dissipation in
the package vs. the ambient temperature for the pack-
ages available.
perature, the package thermal resistance value Theta
JA
(Ө ) is used along with the total die power dissipation.
JA
T
= T + (Ө × P )
Ambient JA D
Junction
2.5
Where T
is the temperature of the working environment.
Ambient
2
In order to determine P , the power dissipated in the load
D
SOIC-8
needs to be subtracted from the total power delivered by
the supplies.
1.5
SOT23-6
P = P
- P
load
D
supply
1
0.5
0
Supply power is calculated by the standard power equa-
tion.
P
= V
× I
supply
supply RMS supply
V
= V - V
S+ S-
-40
-20
0
20
40
60
80
100
120
supply
Ambient Temperature (°C)
Power delivered to a purely resistive load is:
Figure 4. Maximum Power Derating
2
P
= ((V
)
)/Rload
eff
load
LOAD RMS
©2007-2008 CADEKA Microcircuits LLC
www.cadeka.com
14
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
