Technical
Specification
IQ18xxxSKxxx
Application Section
OUTPUT VOLTAGE TRIM (Pin 6): The TRIM input permits the
user to adjust the output voltage across the sense leads up or
down according to the trim range specifications.
PROTECTION FEATURES
Input Under-Voltage Lockout: The converter is designed
to turn off when the input voltage is too low, helping avoid an
input system instability problem, described in more detail in
the application note titled “Input System Instability” on our
website. The lockout circuitry is a comparator with dc hysteresis.
When the input voltage is rising, it must exceed the typical Turn-
On Voltage Threshold value (listed on the specifications page)
before the converter will turn on. Once the converter is on,
the input voltage must fall below the typical Turn-Off Voltage
Threshold value before the converter will turn off.
To decrease the output voltage, the user should connect a
resistor between Pin 6 and Pin 5 (SENSE(-) input). For a desired
decrease of the nominal output voltage, the value of the resistor
should be
511
R
=
- 10.22 (kW)
trim-down
(D%)
where
Vnominal – Vdesired
Vnominal
Output Current Limit: The maximum current limit remains
constant as the output voltage drops. However, once the
impedance of the load across the output is small enough to make
the output voltage drop below the specified Output DC Current-
Limit Shutdown Voltage, the converter turns off.
=
x 100%
D%
To increase the output voltage, the user should connect a
resistor between Pin 6 and Pin 7 (SENSE(+) input). For a desired
increase of the nominal output voltage, the value of the resistor
should be
The converter then enters a “hiccup mode” where it repeatedly
turns on and off at a 5 Hz (nominal) frequency with a 5% duty
cycle until the short circuit condition is removed. This prevents
excessive heating of the converter or the load board.
5.11VOUT (100+D%)
x
511
_
R
_
=
(kW)
trim-up
10.22
)
(
1.225D%
D%
Output Over-Voltage Limit: If the voltage across the output
pins exceeds the Output Over-Voltage Protection threshold, the
converter will immediately stop switching. This prevents damage
to the load circuit due to 1) excessive series resistance in output
current path from converter output pins to sense point, 2) a
release of a short-circuit condition, or 3) a release of a current
limit condition. Load capacitance determines exactly how high
the output voltage will rise in response to these conditions. After
200 ms the converter will automatically restart.
where
V
= Nominal Output Voltage
out
Trim graphs show the relationship between the trim resistor
value and Rtrim-up and Rtrim-down, showing the total range the
output voltage can be trimmed up or down.
Note: the TRIM feature does not affect the voltage at which the
output over-voltage protection circuit is triggered. Trimming the
output voltage too high may cause the over-voltage protection
circuit to engage, particularly during transients.
Over-Temperature Shutdown: A temperature sensor on
the converter senses the average temperature of the module.
The thermal shutdown circuit is designed to turn the converter
off when the temperature at the sensed location reaches the
Over-Temperature Shutdown value. It will allow the converter
to turn on again when the temperature of the sensed location
falls by the amount of the Over-Temperature Shutdown Restart
Hysteresis value.
It is not necessary for the user to add capacitance at the Trim
pin. The node is internally bypassed to eliminate noise.
Total DC Variation of V
specifications, the maximum variation of the dc value of V
: For the converter to meet its full
OUT
,
OUT
due to both trimming and remote load voltage drops, should not
be greater than that specified for the output voltage trim range.
Product # IQ18xxxSKxxx
Phone 1-888-567-9596
www.synqor.com
Doc.# 005-0005462 Rev. C
05/27/10
Page 23
SYNQOR [ SYNQOR WORLDWIDE HEADQUARTERS ]
