Datasheet

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UQQ Series
Wide Input Range Single Output DC-DC Converters
MDC_UQQ.D05 Page 15 of 18
Input Reverse-Polarity Protection
If the input-voltage polarity is accidentally reversed, an internal diode will
become forward biased and likely draw excessive current from the power
source. If the source is not current limited or the circuit appropriately fused, it
could cause permanent damage to the converter.
Pre-Bias Protection
For applications where a pre-bias potential can be present at the output of the
power module it is recommended that either blocking diodes are added in series
with the Vout power lines or, a preferred solution is to use an OR-ing FET control-
ler like the LM5050-1 High-Side & LM5051 Low-Side OR-ing FET Controller from
TI. Starting the module into a pre-bias condition can cause permanent damage
to the module.
Input Fusing
Certain applications and/or safety agencies may require the installation of
fuses at the inputs of power conversion components. Fuses should also be
used if the possibility of a sustained, non-current-limited, input-voltage polarity
reversal exists. For MPS UQQ Series DC-DC Converters, fast-blow fuses are
recommended with values no greater than twice the maximum input current.
Trimming Output Voltage
UQQ converters have a trim capability (pin 6) that enables users to adjust the
output voltage from +10% to –20% (refer to the trim equations). Adjustments
to the output voltage can be accomplished with a single fi xed resistor as shown
in Figures 5 and 6. A single fi xed resistor can increase or decrease the output
voltage depending on its connection. Resistors should be located close to
the converter and have TCR’s less than 100ppm/°C to minimize sensitivity to
changes in temperature. If the trim function is not used, leave the trim pin open.
Standard UQQ’s have a "positive trim" where a single resistor connected from
the Trim pin (pin 6) to the +Sense (pin 7) will increase the output voltage. A
resistor connected from the Trim Pin (pin 6) to the –Sense (pin 5) will decrease
the output voltage.
Trim adjustments greater than the specifi ed +10%/–20% can have an adverse
affect on the converter’s performance and are not recommended. Excessive
voltage differences between V
OUT and Sense, in conjunction with trim adjust-
ment of the output voltage, can cause the overvoltage protection circuitry to
activate (see Performance Specifi cations for overvoltage limits).
Temperature/power derating is based on maximum output current and voltage
at the converter’s output pins. Use of the trim and sense functions can cause
output voltages to increase, thereby increasing output power beyond the UQQ’s
specifi ed rating, or cause output voltages to climb into the output overvoltage
region. Therefore:
(V
OUT at pins) x (IOUT)  rated output power
The Trim pin (pin 6) is a relatively high impedance node that can be susceptible
to noise pickup when connected to long conductors in noisy environments.
LOAD
R
TRIM DOWN
+VOUT
+VIN
–VIN
ON/OFF
CONTROL
TRIM
+SENSE
–VOUT
–SENSE
LOAD
R
TRIM UP
+VOUT
+VIN
–VIN
ON/OFF
CONTROL
TRIM
+SENSE
–VOUT
–SENSE
Figure 5. Trim Connections To Increase Output Voltages Using Fixed Resistors
Figure 6. Trim Connections To Decrease Output Voltages Using Fixed Resistors
UP
VO – 3.3
R
T (k7) =
–10.2
13.3(VO – 1.226)
3.3 – V
O
RT (k7) =
–10.2
16.31
DOWN
UP
VO – 5
R
T (k7) =
–10.2
20.4(VO – 1.226)
5 – VO
RT (k7) =
–10.2
25.01
DOWN
UP
VO – 12
R
T (k7) =
–10.2
49.6(VO – 1.226)
12 – V
O
RT (k7) =
–10.2
60.45
DOWN
UP
VO – 15
R
T (k7) =
–10.2
62.9(VO – 1.226)
15 – V
O
RT (k7) =
–10.2
76.56
DOWN
UQQ-3.3/25-Q12, UQQ-3.3/25-Q48
UQQ-5/17-Q12, UQQ-5/20-Q48
UQQ-12/8-Q12, UQQ-12/8-Q48
UQQ-15/7-Q12
UP
VO – 24
R
T (k7) =
–10.2
101 × (VO – 1.226)
24 – V
O
RT (k7) =
–10.2
124.2
DOWN
UQQ-24/4-Q12
Trim Up Trim Down