HSSR-8400 Datasheet, PDF (13/13 Pages) Agilent(Hewlett-Packard) – 400 V/10 Ohm, General Purpose, 1 Form A, Solid State Relay

Applications Information
Thermal Model
The steady state thermal model
for the HSSR-8400 is shown in
Figure 19. The thermal resistance
values given in this model can be
used to calculate the tempera-
tures at each node for a given
operating condition. The thermal
resistances between the LED and
other internal nodes are very
large in comparison with the
other terms and are omitted for
simplicity. The components do,
however, interact indirectly
through θ_CA, the case-to-ambient
thermal resistance. All heat
generated flows through θ_CA,
which raises the case temperature
T_C accordingly. The value of θ_CA
depends on the conditions of the
board design and is, therefore,
determined by the designer.
The typical value for each output
MOSFET junction-to-case thermal
resistance is specified as 55°C/W.
This is the thermal resistance
from one MOSFET junction to the
case when power is dissipated
equally in the MOSFETs. The
power dissipation in the FET
Driver is negligible in comparison
to the MOSFETs.
On-Resistance and Derating
Curves
The output on-resistance, R_ON,
specified in this data sheet, is the
resistance measured across the
output contact when a pulsed
current signal (I_O = 150 mA) is
applied to the output pins. The
use of a pulsed signal (≤ 30 ms)
implies that each junction temper-
ature is equal to the ambient and
case temperatures. The steady-
state resistance, R_SS, on the other
hand, is the value of the
resistance measured across the
output contact when a DC current
signal is applied to the output
pins for a duration sufficient to
reach thermal equilibrium. R_SS
includes the effects of the tem-
perature rise of each element in
the thermal model.
Derating curves are shown in
Figures 3 and 4. Figure 3 speci-
fies the maximum average output
current allowable for a given
ambient or case temperature.
Figure 4 specifies the output
power dissipation allowable for a
given case temperature. Above a
case temperature of 93°C, the
maximum allowable output
current and power dissipation are
related by the expression
R_SS = P_O(max)/(I_O(max))² from
which R_SS can be calculated.
Staying within the safe area
assures that the steady state
junction temperatures remain less
than 125°C. As an example, for a
case temperature of 100°C,
Figure 4 shows that the output
power dissipation should be
limited to less than 0.5 watts. A
check with Figure 3B shows that
the output current should be
limited to less than 150 mA. This
yields an R_SS of 22 Ω.
Turn On Time Variation
For applications which are
sensitive to turn on time, the
designer should refer to Figures
20 and 21. These figures show
that although there is very little
variation in t_ON within most of the
population, a portion of the
distribution will vary with use.
The optional peaking circuit
shown in Figure 2 can be used to
reduce the total turn on time and,
consequently, any associated
variation.
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