Technical
Specification
IQ12-HPx Family
APPLICATION CONSIDERATIONS
Input system Instability:
This condition can occur because
any dc-dc converter appears incrementally as a negative
resistance load. A detailed application note titled “Input
System Instability” is available on the SynQor website
which
provides an understanding of why this instability arises, and
shows the preferred solution for correcting it.
Application Circuits:
Figure D provides a typical circuit
diagram which details the input filtering and voltage trimming.
Input Filtering and external Capacitance:
Figure E
provides
a diagram showing the internal input filter components. This filter
dramatically reduces input terminal ripple current, which otherwise
could exceed the rating of an external electrolytic input capacitor.
The recommended external input capacitance is specified in the
Input Characteristics section on the Electrical Characteristics
page.
More detailed information is available in the application
note titled “EMI Characteristics” on the SynQor website.
startup Inhibit Period: The Startup Inhibit Period ensures that
the converter will remain off for approximately 200 ms when it is
shut down for any reason. When an output short is present, this
generates a 5 Hz “hiccup mode,” which prevents the converter
from overheating. In all, there are seven ways that the converter
can be shut down, initiating a Startup Inhibit Period:
• Input Under-Voltage Lockout
• Input Over-Voltage Shutdown
• Output Over-Voltage Protection
• Over Temperature Shutdown
• Current Limit
• Short Circuit Protection
• Turned off by the ON/OFF input
Figure F shows three turn-on scenarios, where a Startup Inhibit
Period is initiated at t
0
, t
1
, and t
2
:
V
in(+)
External
Input
Filter
Electrolytic
Capacitor
V
out(+)
V
sense(+)
R
trim-up
or
V
in
ON/OFF
Trim
V
sense(
_
)
V
in(
_
)
V
out(
_
)
R
trim-down
C
load
I
load
Figure D:
Typical application circuit (negative logic unit, permanently enabled).
L
V
in(+)
C
V
in(
_
)
Figure E:
Internal Input Filter Diagram
(component values listed on the specifications page)
.
Product # IQ12xxxHPXxx
Phone 1-888-567-9596
www.synqor.com
Doc.# 005-IQ12HPX Rev. B
04/10/09
Page 26
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