Datasheet

cui.com
date 11/07/2014 │ page 22 of 30CUI Inc │ SERIES: NQB-N │ DESCRIPTION: FULLY REGULATED ADVANCED BUS CONVERTERS
Denition of product operating temperature
The product operating temperature is used to monitor the
temperature of the product, and proper thermal conditions
can be veried by measuring the temperature at positions
P1, P2, P3 and P4. The temperature at these positions (T
P1
,
T
P2
, T
P3
, T
P4
) should not exceed the maximum temperatures
in the table below. The number of measurement points
may vary with different thermal design and topology.
Temperatures above maximum T
P1
, measured at the
reference point P1 (T
P3
/
P3
for base plate versions) are not
allowed and may cause permanent damage.
(Best air ow direction is from positive to negative pins.)
Ambient Temperature Calculation
For products with base plate the maximum allowed
ambient temperature can be calculated by using the
thermal resistance.
1. The power loss is calculated by using the formula
((1/η) - 1) × output power = power losses (P
d
).
η = efciency of product. E.g. 95 % = 0.95
2. Find the thermal resistance (R
th
) in the Thermal
Resistance graph found in the Output section for
each model. Note that the thermal resistance can be
signicantly reduced if a heat sink is mounted on the top
of the base plate.
Calculate the temperature increase (ΔT).
ΔT = R
th
x P
d
3. Max allowed ambient temperature is:
Max T
P1
- ΔT.
E.g. NQB-468 at 2m/s:
1. ((1/0.95) - 1) × 468 W = 24.6 W
2. 19.5 W × 2.8°C/W = 69.0°C}
3. 125 °C - 69.0°C = max ambient temperature is 56°C
The actual temperature will be dependent on several
factors such as the PWB size, number of layers and
direction of airow.
Connections (Top view)
Position Description Max temperature
P1
PWB (reference point, open
frame)
T
P1
=125º C
P2 Opto-coupler T
P2
=105º C
P3
PWB (reference point for
base-plate version)
T
P3
=125º C
P4 Primary MOSFET T
P4
=125º C
Top view
Bottom view
Pin Designation Function
1 +In Positive Input
2 RC Remote Control
3 Case Case to GND (optional)
4 -In Negative Input
5 -Out Negative Output
16 +Out Positive Output
For more information, please visit the product page.