Technical
Specification
IQ18-HPC Family
Before time t
0
, when the input voltage is below the UVL threshold,
the unit is disabled by the Input Under-Voltage Lockout feature.
When the input voltage rises above the UVL threshold, the
Input Under-Voltage Lockout is released, and a Startup Inhibit
Period is initiated. At the end of this delay, the ON/OFF pin is
evaluated, and since it is active, the unit turns on.
At time t
1
, the unit is disabled by the ON/OFF pin, and it cannot
be enabled again until the Startup Inhibit Period has elapsed.
When the ON/OFF pin goes high after t
2
, the Startup Inhibit
Period has elapsed, and the output turns on within the typical
Turn-On Time.
thermal Considerations:
The maximum operating base-
plate temperature, T
B
, is 100 ºC. As long as the user’s thermal
system keeps T
B
<
100 ºC, the converter can deliver its full
rated power.
A power derating curve can be calculated for any heatsink that is
attached to the base-plate of the converter. It is only necessary
to determine the thermal resistance, R
TH
BA
, of the chosen heatsink
between the base-plate and the ambient air for a given airflow
rate. This information is usually available from the heatsink
vendor. The following formula can the be used to determine the
maximum power the converter can dissipate for a given thermal
condition if its base-plate is to be no higher than 100 ºC.
100 ºC - T
A
max
P
diss
=
R
TH
BA
This value of power dissipation can then be used in conjunction
with the data shown in Figure 2 to determine the maximum load
current (and power) that the converter can deliver in the given
thermal condition.
For convenience, power derating curves for an encased converter
without a heatsink and with a typical heatsink are provided for
each output voltage.
V
in
Under-Voltage
Lockout Turn-
On Threshold
ON/OFF
(neg logic)
ON
OFF
ON
OFF
ON
9ms
(typical
V
out
(typical start-up
inhibit period)
200ms
turn on time)
200ms
200ms
t
0
t
1
t
2
t
Figure F:
Startup Inhibit Period (turn-on time not to scale)
Product # IQ18xxxHPCxx
Phone 1-888-567-9596
www.synqor.com
Doc.# 005-005029 Rev. B
04/13/09
Page 27
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