DCDC
09-Sept-14
Application Notes
QSB150350
Thermal Resistance Information
Voltage trim up
Connect trim resistor Rtrim between Trim pin and -Sense pin.
Where: R trim up/down is the external resistor in kΩ. Vnom is the nominal output voltage. Vdes is the desired output voltage. R1, R2, R3 and Vr
are internal to the unit and are defined in the table below.
Voltage trim down
Connect trim resistor Rtrim between Trim pin and +Sense pin
Voltage trim up - Voltage trim up, Connect trim resistor
Rtrim between Trim pin and +Sense pin.
Voltage trim down - Connect trim resistor Rtrim between Trim pin
and –Sense pin
R trim up =
V
des - Vnom
R2 x R3
(kΩ)
R2 + R3
-
R1 Vr - Vf
R2
R2 + R3
R trim down =
V
nom - Vdes
- R2 (kΩ)
R1 x (V
des - Vr)
R trim down =
kΩ
- 10.22
511
%
Vnom - Vdes
Vnom
Where:
%= x 100
R trim up =
kΩ
--
k x
%
511
10.22
5.11 V
nom (100 +
%)
%
Vdes - Vnom
Vnom
Where:
%= x 100
Output Voltage (V)
R1(kΩ) R2 (kΩ) R3 (kΩ)
Vr (V) Vf (V)
3.3 V 3.00 12.0 4.3 1.24 0.46
5.0 V 2.32 3.3 0.0 2.5 0.0
12.0 V 9.10 51.0 5.1 2.5 0.46
15.0 V 12.0 56.0 8.25 2.5 0.46
24.0 V 20.0 100.0 7.5 2.5 0.46
Output Voltage Trim QSB100, QSB200 & QSB350 Series
Air Flow Rate
Typical R
ca
Natural Convection
20 ft. / min (0.1 ms)
7.12 °C/W
100 ft./min (0.5 ms) 6.21 °C/W
200 ft./min (1.0 ms) 5.17 °C/W
300 ft./min (1.5 ms) 4.29 °C/W
400 ft./min (2.0 ms) 3.64 °C/W
500 ft./min (2.5 ms) 2.96 °C/W
600 ft./min (3.0 ms) 2.53 °C/W
700 ft./min (3.5 ms) 2.37 °C/W
800 ft./min (4.0 ms) 2.19 °C/W
R
ca
=
Thermal resistance case to ambient
0
5
10
1
5
2
0
25
30
35
4
0
45
50
0 10 20 30 40 50 60 70 80 90 100
Power Dissipated ,Pd (W)
N
atural Convection
20 ft./min. (0.1 m/s)
100 ft./min. (0.5 m/s)
200 ft./min. (1.0 m/s)
300 ft./min. (1.5 m/s)
400 ft./min. (2.0 m/s)
500 ft./min. (2.5 m/s)
600 ft./min. (3.0 m/s)
7
00 ft./min. (3.5 m/s)
8
00 ft./min. (4.0 m/s)
Ambient Temperature ,Ta (ºC)
Maximum Power Dissipation vs Ambient Temperature and Air Flow without heatsink
Derating Curve
Output Voltage Trim QSB75 & QSB150 Series
Value QSB100/200 QSB350
k 1.225 1.24
