Technical Specification
Quarter
48V 3.3/1.8V
77W
out
in
Brick Dual
Resistor values in Kohms for the desired increase/decrease
(typical) in output voltage (%)
excessive heating of the converter or the load board.
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 dam-
age 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 cur-
rent 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.
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.
Total DC Variation of Vout: For the converter to meet its
full specifications, the maximum variation of the DC value of
Vout, due to both trimming and remote load voltage drops,
should not be greater than that specified for the output voltage
trim range.
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.
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”. The lockout cir-
cuitry is a comparator with DC hysteresis. When the input volt-
age is rising, it must exceed the typical Turn-On Voltage
Threshold value (listed on the specification page) before the
converter will turn on. Once the converter is on, the input volt-
age must fall below the typical Turn-Off Voltage Threshold value
before the converter will turn off.
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 web site
(www.synqor.com) which provides an understanding of why
this instability arises, and shows the preferred solution for cor-
recting it.
Output Current Limit: The maximum current limit remains
constant as the output voltage drops. However, once the imped-
ance of the short 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.
Application Circuits: Figure D below provides a typical cir-
cuit diagram which details the input filtering and voltage trim-
ming.
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
Vin(+)
3.3 Vout(+)
Iload
Rtrim-up
Electrolytic
Capacitor
Trim
Cload
33µF
External
Input
ESR
1Ω
Vin
OP RTN
ON/OFF
Filter
or
Rtrim-down
Cload
_
Iload
1.8 Vout(+)
Vin( )
Figure D: Typical application circuit (negative logic unit, permanently enabled).
Product # DQ63318QGL08
Phone 1-888-567-9596
Doc.# 005-2DQ638D Rev. B
10/7/03
Page 12
SYNQOR [ SYNQOR WORLDWIDE HEADQUARTERS ]
