UHP28_2_12A Datasheet, PDF (6/9 Pages) Murata Manufacturing Co., Ltd. – Isolated, 12 Amp Half Brick, 48VIN/28.2VOUT DC/DC Converters

UHP-28.2/12-D48
Isolated, 12 Amp Half Brick, 48VIN/28.2VOUT DC/DC Converters
Short Circuit Condition
When a converter is in current-limit mode, the output voltage will drop as
the output current demand increases. If the output voltage drops too low, the
magnetically coupled voltage used to develop primary side voltages will also
drop, thereby shutting down the PWM controller. Following a time-out period,
the PWM will restart causing the output voltage to begin ramping to their
appropriate value. If the short-circuit condition persists, another shutdown
cycle will be initiated. This on/off cycling is referred to as "hiccup" mode. The
hiccup cycling reduces the average output current, thereby preventing internal
temperatures from rising to excessive levels. The UHP Series is capable of
enduring an indefinite short circuit output condition.
Features and Options
Remote Sense
Note: The Sense and VOUT lines are internally connected through resistors
(=<107). Nevertheless, if the sense function is not used for remote regulation
the user should connect the +Sense to +VOUT and –Sense to –VOUT at the DC/
DC converter pins.
UHP Series converters employ a sense feature to provide point of use regula-
tion, thereby overcoming moderate IR drops in pcb conductors or cabling.
The remote sense lines carry very little current and therefore require minimal
cross-sectional-area conductors. The sense lines, which are capacitively
coupled to their respective output lines, are used by the feedback control-loop
to regulate the output. As such, they are not low impedance points and must
be treated with care in layouts and cabling. Sense lines on a pcb should be
run adjacent to dc signals, preferably ground. In cables and discrete wiring
applications, twisted pair or other techniques should be implemented.
1 _–INPUT
3 _ON/OFF
CONTROL
4
+INPUT
+OUTPUT
Contact and PCB resistance
losses due to IR drops
5
6
+SENSE
TRIM 7
8
–SENSE
9
–OUTPUT
IOUT
Sense Current
Sense Return
IOUT Return
LOAD
Contact and PCB resistance
losses due to IR drops
Figure 4. Remote Sense Circuit Configuration
UHP Series converters will compensate for drops between the output voltage
at the DC/DC and the sense voltage at the DC/DC provided that:
[VOUT (+) –VOUT (–)] –[Sense(+) –Sense (–)] =< 10% VOUT
Output overvoltage protection is monitored at the output voltage pin, not the
Sense pin. Therefore, excessive voltage differences between VOUT and Sense
in conjunction with trim adjustment of the output voltage can cause the
overvoltage protection circuitry to activate (see Performance Specifications for
overvoltage limits). Power derating is based on maximum output current and
voltage at the converter's output pins. Use of trim and sense functions can
cause output voltages to increase, thereby increasing output power beyond
the conveter's specified rating, or cause output voltages to climb into the
output overvoltage region. Therefore, the designer must ensure:
(VOUT at pins) x (IOUT ) =< rated output power
On/Off Control
The primary-side, Remote On/Off Control function (pin 3) can be specified to
operate with either positive or negative polarity. Positive-polarity devices ("P"
suffix) are enabled when pin 3 is left open or is pulled high. Positive-polarity
devices are disabled when pin 3 is pulled low (0-0.8V with respect to –Input).
Negative-polarity devices are off when pin 3 is high/open and on when pin 3
is pulled low or grounded. See Figure 5.
4 +INPUT
+
3
ON/OFF
CONTROL
EQUIVALENT CIRCUIT FOR
POSITIVE AND NEGATIVE
LOGIC MODELS
CONTROL
1 _–INPUT
REF
Figure 5. Driving the On/Off Control Pin
Dynamic control of the remote on/off function is best accomplished with
a mechanical relay or an open-collector/open-drain drive circuit (optically
isolated if appropriate). The drive circuit should be able to sink appropri-
ate current (see Performance Specifications) when activated and withstand
appropriate voltage when deactivated.
Trimming Output Voltage
UHP converters have a trim capability (pin 7) that allows users to adjust the
output voltage within the specified range. Adjustments to the output voltages
can be accomplished via a trim pot (Figure 6) or a single fixed resistor, shown
in Figures 7 and 8. A single fixed resistor can increase or decrease the output
voltage depending on its connection. The resistor should be located close to
the converter and have a TCR less than 100ppm/°C to minimize sensitivity to
temperature changes. If the trim function is not used, leave the trim pin floating.
A single resistor connected from the Trim (pin 7) to the +Sense (pin 6), will
increase the output voltage (Figure 8). A resistor connected from the Trim (pin
9) to the –Sense (pin 8), will decrease the output voltage (Figure 9).
Trim adjustments greater than the specified range can have an adverse affect
on the converter's performance and are not recommended. Excessive voltage
differences between VOUT and Sense, in conjunction with trim adjustment of
the output voltage, can cause the overvoltage protection circuitry to activate
(see Performance Specifications for overvoltage limits). Power derating is
based on maximum output current and voltage at the converter's output
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