Datasheet
PAE Series
Up to 100W 29.8V Nom Output Eighth-Brick Isolated
DC-DC Converter with 2:1 Wide Input Range
MDC_PAE Series.A01 Page 15 of 17
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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 PAE’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.
Remote Sense Input
Use the Sense inputs with caution. Sense is normally connected at the load.
Sense inputs compensate for output voltage inaccuracy delivered at the load.
This is done by correcting IR voltage drops along the output wiring and the
current carrying capacity of PC board etch. This output drop (the difference
between Sense and Vout when measured at the converter) should not exceed
0.5V. Consider using heavier wire if this drop is excessive. Sense inputs also
improve the stability of the converter and load system by optimizing the control
loop phase margin.
Note: The Sense input and power Vout lines are internally connected through
low value resistors to their respective polarities so that the converter can
operate without external connection to the Sense. Nevertheless, if the Sense
function is not used for remote regulation, the user should connect +Sense to
+Vout and –Sense to –Vout at the converter pins.
The remote Sense lines carry very little current. They are also capacitively
coupled to the output lines and therefore are in the feedback control loop to
regulate and stabilize the output. As such, they are not low impedance inputs
and must be treated with care in PC board layouts. Sense lines on the PCB
should run adjacent to DC signals, preferably Ground. In cables and discrete
wiring, use twisted pair, shielded tubing or similar techniques.
Any long, distributed wiring and/or signifi cant inductance introduced into the
Sense control loop can adversely affect overall system stability. If in doubt, test
Figure 6. Remote Sense Circuit Confi guration
LOAD
Contact and PCB resistance
losses due to IR drops
Contact and PCB resistance
losses due to IR drops
+Vout
+SENSE
TRIM
−
SENSE
-Vout
+
Vin
ON/OFF
CONTROL
–Vin
Sense Current
I OUT
Sense Return
I OUT Return
LOAD
R
TRIM UP
+Vout
+Vin
–Vin
ON/OFF
CONTROL
TRIM
+SENSE
–Vout
–SENSE
Figure 4. Trim Connections To Increase Output Voltages Using Fixed Resistors
LOAD
R
TRIM DOWN
+Vout
+Vin
–Vin
ON/OFF
CONTROL
TRIM
+SENSE
–Vout
–SENSE
Figure 5. Trim Connections To Decrease Output Voltages Using Fixed Resistors
Trim Equations
Where,
' _VNOM − VOUT) / VNOM _
VNOM is the nominal, untrimmed output voltage.
V
OUT 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.
Trim Down
Connect trim resistor between
trim pin and −Sense
'
5.11
R
TrimDn
(k Ω) =
− 10.22
Trim Up
Connect trim resistor between
trim pin and +Sense
1.225 × '
5.11 × VNOM × (1+'
R
TrimUp
(k Ω) =
− 10.22
'
− 5.11