Datasheet

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UEE 150W Series
Isolated, High-Density, Eighth-Brick
DOSA Low Profi le DC-DC Converters
MDC_UEE 150W_Series.A02 Page 33 of 35
Please observe Sense inputs tolerance to avoid improper operation:
[Vout(+) −Vout(-)] − [Sense(+) −Sense(-)] ≤ 10% of Vout
Output overvoltage protection is monitored at the output voltage pin, not the
Sense pin. Therefore excessive voltage differences between Vout and Sense
together with trim adjustment of the output can cause the overvoltage protec-
tion circuit to activate and shut down the output.
Power derating of the converter is based on the combination of maximum
output current and the highest output voltage. Therefore the designer must
insure:
(Vout at pins) x (Iout)
≤ (Max. rated output power)
Trimming the Output Voltage
The Trim input to the converter allows the user to adjust the output voltage
over the rated trim range (please refer to the Specifi cations). In the trim equa-
tions and circuit diagrams that follow, trim adjustments use either a trimpot or
a single fi xed resistor connected between the Trim input and either the +Sense
or –Sense terminals. Trimming resistors should have a low temperature coef-
fi cient (±100 ppm/deg.C or less) and be mounted 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 specifi ed 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. Be particularly careful with a trimpot. 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.
Where,
Δ = | (V
NOM − VOUT) / VNOM |
VNOM is the nominal, untrimmed output voltage.
VOUT is the desired new output voltage.
Do not exceed the specified trim range or maximum power ratings when adjusting trim.
Use 1% precision resistors mounted close to the converter on short leads.
If sense is not installed, connect the trim resistor to the respective V
OUT pin.
Trim Down
Connect trim resistor between
trim pin and −Sense
Δ
5.11
R
TrimDn
(k Ω) =
− 10.22
Trim Up
Connect trim resistor between
trim pin and +Sense
1.225 × Δ
5.11 × VNOM × (1+Δ)
R
TrimUp
(k Ω) =
− 10.22
Δ
− 5.11
Figure 8. Trim Connections Using A Trimpot
LOAD
+VOUT
+VIN
–VIN
ON/OFF
CONTROL
TRIM
+SENSE
–VOUT
–SENSE
Trim Equations
Trim Circuits
Figure 9. Trim Connections To Increase Output Voltages
LOAD
R
TRIM UP
+VOUT
+VIN
–VIN
ON/OFF
CONTROL
TRIM
+SENSE
–VOUT
–SENSE
Connect sense to its respective VOUT pin if sense is not used with a remote load.