HPQ-12/25-D48 Series
Isolated 300-Watt Quarter Brick DC/DC Converters
close to the converter. Keep leads short. If the trim function is not used, leave
the trim unconnected. With no trim, the converter will exhibit its specified output
voltage accuracy.
There are two CAUTIONs to observe for the Trim input:
CAUTION: To avoid unplanned power down cycles, do not exceed EITHER the
maximum output voltage OR the maximum output power when setting the trim.
If the output voltage is excessive, the OVP circuit may inadvertantly shut down
the converter. If the maximum power is exceeded, the converter may enter
current limiting. If the power is exceeded for an extended period, the converter
may overheat and encounter overtemperature shut down.
CAUTION: Be careful of external electrical noise. The Trim input is a senstive
input to the converter’s feedback control loop. Excessive electrical noise may
cause instability or oscillation. Keep external connections short to the Trim
input. Use shielding if needed.
Trim Equations
R
adj_up
(in kΩ) =
V
nominal
x (1+Δ) - 1 - 2
1.225 x Δ
Δ
where Δ =
V
out
-V
nominal
V
nominal
ON/OFF
CONTROL
+OUTPUT
-INPUT
+SENSE
TRIM
R
TRIM DOWN
-SENSE
LOAD
+INPUT
-OUTPUT
Figure 5. Trim adjustments to Decrease Output Voltage using a Fixed Resistor
Remote On/Off Control
On the input side, a remote On/Off Control can be specified with either positive
or negative logic as follows:
Positive: Models equipped with Positive Logic are enabled when the On/Off
pin is left open or is pulled high to +15V
DC
with respect to –V
IN
. An internal
bias current causes the open pin to rise to +V
IN
. Positive-polarity devices are
disabled when the On/Off is grounded or brought to within a low voltage (see
Specifications) with respect to –V
IN
.
Negative: Models with negative polarity are on (enabled) when the On/Off is
grounded or brought to within a low voltage (see Specifications) with respect to
–V
IN
. The device is off (disabled) when the On/Off is left open or is pulled high
to +15V
DC
Max. with respect to –V
IN
.
Dynamic control of the On/Off function should be able to sink the specified
signal current when brought low and withstand specified voltage when brought
high. Be aware too that there is a finite time in milliseconds (see Specifications)
between the time of On/Off Control activation and stable, regulated output. This
time will vary slightly with output load type and current and input conditions.
There are two CAUTIONs for the On/Off Control:
1
R
adj_down
(in kΩ) = - 2
Δ
V
nominal
-V
out
where Δ =
V
nominal
Where Vo = Desired output voltage. Adjustment accuracy is subject to resistor
tolerances and factory-adjusted output accuracy. Mount trim resistor close
to converter. Use short leads. Note that “Δ” is given as a small fraction, not a
percentage.
+OUTPUT
-INPUT
+SENSE
ON/OFF
CONTROL
TRIM
R
TRIM UP
-SENSE
LOAD
CAUTION: While it is possible to control the On/Off with external logic if you
carefully observe the voltage levels, the preferred circuit is either an open
drain/open collector transistor or a relay (which can thereupon be controlled by
logic). The On/Off prefers to be set at approx. +15V (open pin) for the ON state,
assuming positive logic.
CAUTION: Do not apply voltages to the On/Off pin when there is no input power
voltage. Otherwise the converter may be permanently damaged.
+INPUT
-OUTPUT
Figure 4. Trim adjustments to Increase Output Voltage using a Fixed Resistor
www.murata-ps.com
26 Jul 2010
email: sales@murata-ps.com
MDC_HPQ-12/25-D48 Series.A02
Page 11 of 12
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