EL5221C
Dual 12MHz Rail-to-Rail Input-Output Buffer
determine if load conditions need to be modified for the
buffer to remain in the safe operating area.
the device’s power derating curves. To ensure proper
operation, it is important to observe the recommended
derating curves shown in Figure 3 and Figure 4.
The maximum power dissipation allowed in a package is
determined according to:
Package Mounted on a JEDEC JESD51-7 High
Effective Thermal Conductivity Test Board
T
– T
AMAX
1
JMAX
P
= --------------------------------------------
DMAX
870mW
Θ
MAX T =125°C
J
JA
0.8
where:
TJMAX = Maximum Junction Temperature
AMAX= Maximum Ambient Temperature
JA = Thermal Resistance of the Package
DMAX = Maximum Power Dissipation in the
0.6
435mW
0.4
T
Θ
0.2
0
P
Package
0
25
50
75 85 100
125
150
Ambient Temperature (°C)
The maximum power dissipation actually produced by
an IC is the total quiescent supply current times the total
power supply voltage, plus the power in the IC due to the
loads, or:
Figure 3. Package Power Dissipation vs
Ambient Temperature
P
= Σi[V × I
+ (V + – V
i) × I
i]
DMAX
S
SMAX
S
OUT
LOAD
Package Mounted on a JEDEC JESD51-3 Low
Effective Thermal Conductivity Test Board
when sourcing, and
0.6
P
= Σi[V × I
+ (V
i – V -) × I
OUT S
i]
DMAX
S
SMAX
LOAD
MAX T =125°C
J
486mW
391mW
0.5
0.4
0.3
0.2
0.1
0
when sinking.
where:
i = 1 to 2 for Dual Buffer
VS = Total Supply Voltage
I
SMAX = Maximum Supply Current Per Channel
VOUTi = Maximum Output Voltage of the
0
25
50
75 85 100
125
150
Application
Ambient Temperature (°C)
ILOADi = Load Current
Figure 4. Package Power Dissipation vs
Ambient Temperature
If we set the two PDMAX equations equal to each other,
we can solve for RLOADi to avoid device overheat. Fig-
ure 3 and Figure 4 provide a convenient way to see if the
device will overheat. The maximum safe power dissipa-
tion can be found graphically, based on the package type
and the ambient temperature. By using the previous
equation, it is a simple matter to see if PDMAX exceeds
Unused Buffers
It is recommended that any unused buffer have the input
tied to the ground plane.
11
ELANTEC [ ELANTEC SEMICONDUCTOR ]
