13
FN6838.1
September 8, 2015
ON the outputs by putting them in a low impedance (normal)
operating state.
Driving Capacitive Loads
As load capacitance increases, the -3dB bandwidth will
decrease and peaking can occur. Depending on the
application, it may be necessary to reduce peaking and to
improve device stability. To improve device stability a
snubber circuit or a series resistor may be added to the
output of the EL5420T.
A snubber is a shunt load consisting of a resistor in series
with a capacitor. An optimized snubber can improve the
phase margin and the stability of the EL5420T. The
advantage of a snubber circuit is that it does not draw any
DC load current or reduce the gain.
Another method to reduce peaking is to add a series output
resistor (typically between 1 to 10). Depending on the
capacitive loading, a small value resistor may be the most
appropriate choice to minimize any reduction in gain.
Power Dissipation
With the high-output drive capability of the EL5420T
amplifiers, it is possible to exceed the +150°C absolute
maximum junction temperature under certain load current
conditions. It is important to calculate the maximum power
dissipation of the EL5420T in the application. Proper load
conditions will ensure that the EL5420T junction temperature
stays within a safe operating region.
The maximum power dissipation allowed in a package is
determined according to Equation 1:
where:
•T
JMAX
= Maximum junction temperature
•T
AMAX
= Maximum ambient temperature
•
JA
= Thermal resistance of the package
•P
DMAX
= Maximum power dissipation allowed
The total power dissipation produced by an IC is the total
quiescent supply current times the total power supply
voltage, plus the power dissipation in the IC due to the loads,
or:
when sourcing, and:
when sinking,
where:
• i = 1 to 4
(1, 2, 3, 4 corresponds to Channel A, B, C, D respectively)
•V
S
= Total supply voltage (V
S
+ - V
S
-)
•V
S
+ = Positive supply voltage
•V
S
- = Negative supply voltage
•I
SMAX
= Maximum supply current per amplifier
(I
SMAX
= EL5420T quiescent current ÷ 4)
•V
OUT
= Output voltage
•I
LOAD
= Load current
Device overheating can be avoided by calculating the
minimum resistive load condition, R
LOAD
, resulting in the
highest power dissipation. To find R
LOAD
set the two P
DMAX
equations equal to each other and solve for V
OUT
/I
LOAD
.
Reference the package power dissipation curves, Figures 30
and 31, for further information.
P
DMAX
T
JMAX
T
AMAX
–
JA
---------------------------------------------
=
(EQ. 1)
P
DMAX
iV
S
I
SMAX
V
S
+V
OUT
i I
LOAD
i–+=
(EQ. 2)
P
DMAX
iV
S
I
SMAX
V
OUT
iV
S
- I
LOAD
i–+=
(EQ. 3)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 25 50 75 100 125 150
Ambient Temperature (°C)
Power Dissipation (W)
FIGURE 30. PACKAGE POWER DISSIPATION vs AMBIENT
TEMPERATURE
JEDEC JESD51-3 LOW EFFECTIVE THERMAL
CONDUCTIVITY TEST BOARD
1.04W
962mW
833mW
JA
= 120°C/W
SOIC14
JA
= 150°C/W
TSSOP14
JA
= 130°C/W
QFN16
85
FIGURE 31. PACKAGE POWER DISSIPATION vs AMBIENT
TEMPERATURE
JEDEC JESD51-7 HIGH EFFECTIVE THERMAL
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 25 50 75 100 125 150
Ambient Temperature (°C)
Power Dissipation (W)
2.66W
1.42W
1.25W
JA
= 47°C/W
QFN16
JA
= 100°C/W
TSSOP14
JA
= 88°C/W
SOIC14
85
EL5420T
