EL5421_07 Datasheet, PDF (10/12 Pages) Intersil Corporation – Quad 12MHz Rail-to-Rail Input-Output Buffer

EL5421
dissipation could easily increase such that the device may
be damaged. Maximum reliability is maintained if the output
continuous current never exceeds ±30mA. This limit is set by
the design of the internal metal interconnects.
Output Phase Reversal
The EL5421 is immune to phase reversal as long as the
input voltage is limited from V_S- -0.5V to V_S+ +0.5V. Figure
24 shows a photo of the output of the device with the input
voltage driven beyond the supply rails. Although the device's
output will not change phase, the input's overvoltage should
be avoided. If an input voltage exceeds supply voltage by
more than 0.6V, electrostatic protection diodes placed in the
input stage of the device begin to conduct and overvoltage
damage could occur.
1V
10µs
V_S=±2.5V
T_A=25°C
1V
V_IN=6V_P-P
FIGURE 24. OPERATION WITH BEYOND-THE-RAILS INPUT
Power Dissipation
With the high-output drive capability of the EL5421 buffer, it
is possible to exceed the +125°C 'absolute-maximum
junction temperature' under certain load current conditions.
Therefore, it is important to calculate the maximum junction
temperature for the application to determine if load
conditions need to be modified for the buffer to remain in the
safe operating area.
The maximum power dissipation allowed in a package is
determined according to:
P_DMAX
=
T_{----J---M-----A----X-----–-----}T_{----A---M-----A----X--}
Θ_JA
(EQ. 1)
where:
T_JMAX = Maximum junction temperature
T_AMAX = Maximum ambient temperature
θ_JA = Thermal resistance of the package
P_DMAX = Maximum power dissipation in the package
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:
P_DMAX = Σi[V _S × I_SMAX + (V _S+ – V_OUTi ) × I_LOADi ] (EQ. 2)
when sourcing, and:
P_DMAX = Σi[V_S × I_SMAX + (V_OUTi – V_S- ) × I_LOADi ]
(EQ. 3)
when sinking.
Where:
i = 1 to 4 for quad
V_S = Total supply voltage
I_SMAX = Maximum supply current per channel
V_OUTi = Maximum output voltage of the application
I_LOADi = Load current
If we set the two P_DMAX equations equal to each other, we
can solve for R_LOADi to avoid device overheat. Figures 25
and 26 provide a convenient way to see if the device will
overheat. The maximum safe power dissipation 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 P_DMAX exceeds the device's power
derating curves. To ensure proper operation, it is important
to observe the recommended derating curves shown in
Figures 25 and 26.
JEDEC JESD51-7 HIGH EFFECTIVE THERMAL
CONDUCTIVITY TEST BOARD
1
0.9
0.8 ^870mW
0.7
0.6
0.5
θ_{JA =1M15S°OCP/W10}
0.4
0.3
0.2
0.1
0
0
25
50
75 85 100
125
AMBIENT TEMPERATURE (°C)
FIGURE 25. PACKAGE POWER DISSIPATION vs AMBIENT
TEMPERATURE
10
FN7198.2
August 2, 2007