EL4430C EL4431C
Video Instrumentation Amplifiers
Applications Information
Power Supplies
The instrumentation amplifiers work well on any
supplies from
g
3V to
g
15 The supplies may be
of different voltages as long as the requirements
of the Gnd pin are observed ( see the Ground Pin
section for a discussion) The supplies should be
bypassed close to the device with short leads
4 7mF tantalum capacitors are very good and no
smaller bypasses need be placed in parallel Ca-
pacitors as low as 0 01mF can be used if small
load currents flow
Single-polarity supplies such as
a
12V with
a
5V can be used where the ground pin is con-
nected to
a
5V and V- to ground The inputs and
outputs will have to have their levels shifted
above ground to accommodate the lack of nega-
tive supply
The dissipation of the amplifiers increases with
power supply voltage and this must be compati-
ble with the package chosen This is a close esti-
mate for the dissipation of a circuit
P
D
e
2
c
V
S
c
I
S
max
a
(V
S
b
V
O
)
c
V
O
R
PAR
where I
S
max is the maximum supply current
V
S
is the
g
supply voltage
(assumed equal)
V
O
is the output voltage
R
PAR
is the parallel of all resistors
loading the output
For instance the EL4431 draws a maximum of
16 mA and we might require a 2V peak output
into 150X and a 270X
a
270X feedback divider
The R
PAR
is 117X The dissipation with
g
5V
supplies is 201 mW The maximum supply volt-
age that the device can run on for a given P
D
and
the other parameter is
V
S
max
e
(P
D
a
V
O
2 R
PAR
)
(2I
S
a
V
O
R
PAR
)
Contd
The maximum dissipation a package can offer is
P
D
max
e
(T
J
max
b
T
A
max)
i
JA
where T
J
max is the maximum die junction
temperature 150 C for reliability less to
retain optimum electrical performance
T
A
max is the ambient temperature 70 C
for commercial and 85 C for industrial
range
i
JA
is the thermal resistance of the
mounted package obtained from data-
sheet dissipation curves
The more difficult case is the SO-8 package With
a maximum die temperature of 150 C and a maxi-
mum ambient temperature of 85 C the 65 C tem-
perature rise and package thermal resistance of
170 C W gives a dissipation of 382 mW at 85 C
This allows a maximum supply voltage of
g
8 5V
for the EL4431 operated in our example If an
%
)
EL4430 were driving a light load (R
PAR
it could operate on
g
15V supplies at a 70 C max-
imum ambient
x
Output Loading
The output stage of the instrumentation amplifi-
ers is very powerful It typically can source
80 mA and sink 120 mA Of course this is too
much current to sustain and the part will eventu-
ally be destroyed by excessive dissipation or by
metal traces on the die opening The metal traces
are completely reliable while delivering the
30 mA continuous output given in the Absolute
Maximum Ratings table in this datasheet or
higher purely transient currents
Gain or gain accuracy degrades only 10% from
no load to 100X load Heavy resistive loading will
degrade frequency response and video distortion
for loads
k
100X
Capacitive loads will cause peaking in the fre-
quency response If capacitive loads must be driv-
en a small-valued series resistor can be used to
isolate it (12X to 51X should suffice) A 22X se-
ries resistor will limit peaking to 2 5 dB with
even a 220 pF load
9
ELANTEC [ ELANTEC SEMICONDUCTOR ]
