Technical Specification
Quarter
Brick
Note: the output over-voltage protection circuit senses the volt-
age across the output (pins 8 and 4) to determine when it
should trigger, not the voltage across the converter’s sense
leads (pins 7 and 5). Therefore, the resistive drop on the board
should be small enough so that output OVP does not trigger,
even during load transients.
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.
To decrease the output voltage, the user should connect a resis-
tor between Pin 6 and Pin 5 (SENSE(-) input). For a desired
decrease of the nominal output voltage, the value of the resis-
tor should be
48Vin 15Vout 6.7A
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.
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 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.
511
R
trim-down
=
- 10.22 (kΩ)
∆%
( )
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.
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.
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.
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.
where
∆%
=
(
Vnominal – Vdesired
)
x
100%
Vnominal
To increase the output voltage, the user should connect a resis-
tor between Pin 6 and Pin 7 (SENSE(+) input). For a desired
increase of the nominal output voltage, the value of the resistor
should be
R
trim-up
=
where
(
5.11V
OUT
(
100+
∆
%
)
_
511
_
10.22
1.225
∆
%
∆
%
V
OUT
= Nominal Output Voltage
)
(kΩ)
Figure C graphs the relationship between the trim resistor value
and Rtrim-up and Rtrim-down, showing the total range the out-
put voltage can be trimmed up or down.
100,000
Trim Resistance
(kOhms)
10,000
1,000
100
10
0
2
4
6
8
10
12
14
16
18
20
% increase Vout
% decrease Vout
Figure C: Trim Graph for 15Vout module
Product # PQ48150QGA07
Phone 1-888-567-9596
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
Doc.# 005-2QG415D Rev. D
8/16/02
Page 10
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