Technical Reference Note
Trim Characteristics
Rev.10.13.14_#1.1
AVE240C-48S12
Page 20
Connecting an external resistor between Trim pin and Vo- pin will decrease the output voltage. While connecting it between
Trim and Vo+ will increase the output voltage. The following equations determine the external resistance to obtain the
trimmedoutput voltage.
1
Radj−down
=
− 2(kΩ)
∆
Vnom
×
1+ ∆
1+ 2∆
Radj−up
=
−
(kΩ)
1.225×∆
Vnom −Vdesired
∆
∆ =
Vnom
Vnom
: Nominal output voltage.
For example, to get 13.2V output, the trimmingresistor is
12 ×
1.225×0.1
1+ 2 ×0.1
Radj−up
=
−
(kΩ) = 95.75kΩ
0.1
The output voltage can also be trimmed by potential applied at the Trim pin.
VO = (Vtrim +1.225)×9.8
Where Vtim is the potential applied at the Trim pin, and Vo is the desired output voltage.
Vo+
S+
Vo+
S+
Load
Load
R trim _down
Trim
Trim
R trim _up
Cout
Cout
S-
S-
Vo-
Vo-
Figure 17 Trim up
Figure 18 Trim down
When trimmingup, the output current should be decreased accordingly so as not to exceed the maximum output power
and the minimum input voltage should be increased as shown in Figure 19.
13.2
12.9
36
38
48
Input voltage(V)
Figure 19 Output trim voltagevs. input voltage
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