Datasheet

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ULS 30-Watt Series
Sixteenth-brick DOSA-Compatible,
Isolated DC/DC Converters
MDC_ULS-30W_C07 Page 27 of 30
DOWN
RT (k:) =
Where ∆%  _(  × 100 )_
– 10.22
∆%
511
Trim Down
Trim Equations
Trim Up
UP
RT (k:) =
–
1.225 × ∆%
5.11 × VNOM × (100 + ∆%)
∆%
511
– 10.22
VNOM – VDES
VNOM
Note: “∆%” is always a positive value.
“V
NOM” is the nominal, rated output voltage.
“V
DES” is the desired, changed output voltage.
Remote Sense (ULS-3.3/8-D48 and ULS-5/6-D48 models only)
Note: The Sense and VOUT lines are internally connected through low-value
resistors. Nevertheless, if the sense function is not used for remote regula-
tion the user should connect the +Sense to +V
OUT and –Sense to –VOUT at
the DC/DC converter pins. ULS series converters employ a sense feature to
provide point of use regulation, 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.
[V
OUT(+)-VOUT(–)] – [Sense(+)-Sense(–)]  10%VOUT
In cables and discrete wiring applications, twisted pair or other techniques
should be used. Output over-voltage protection is monitored at the output volt-
age pin, not the Sense pin. Therefore, excessive voltage differences between
V
OUT and Sense in conjunction with trim adjustment of the output voltage can
cause the over-voltage protection circuitry to activate (see Performance Speci-
fi cations for over-voltage limits). Power derating is based on maximum output
current and voltage at the converter’s output pins. Use of trim and sense func-
tions can cause output voltages to increase, thereby increasing output power
beyond the converter’s specifi ed rating, or cause output voltages to climb into
the output over-voltage region. Therefore, the designer must ensure:
(V
OUT at pins) x (IOUT)  rated output power
LOAD
+VOUT
+VIN
Sense Current
Contact and PCB resistance
losses due to IR drops
Contact and PCB resistance
losses due to IR drops
Sense Return
–VIN
ON/OFF
CONTROL
TRIM
+SENSE
–VOUT
–SENSE
I
OUT Return
I
OUT
Figure 7. Remote Sense Circuit Confi guration