Specifications

OUTPUT MODULE V
ref
R
TH
VI-200/VI-J00 ≥3.3V 2.50V 10.0 kΩ
VI-200/VI-J00 <3.3V 0.97V 3.88kΩ
2
nd
Generation (Pre-Defined) 1.23V 1.0 kΩ
2
nd
Generation (User Defined) 1.23V Consult Factory
Table 1. Module Internal Reference Voltages and Thevenin Resistances.
Example:
±±
10% Trim adjust on a 12V nominal output.
Figure 11 shows a typical variable Trim circuit. Using a 10k trimpot (R7), the resistor values for R6 and R8 can be calculat-
ed as follows:
V
1
= V
ref
+ 10% = 2.75V Given: V
ref
= 2.5V (see Table 1)
I
R5
= (2.75V - V
ref
)/R
TH
= (2.75V - 2.5V)/10kΩ = 25µA
Setting the bottom limit:
V
R6
= 2.5V - 10% = 2.25V
And since I
R5
= I
R6
= 25µA,
R6 = V
R6
/I
R6
= 2.25V/25µA = 90kΩ
V
2
= V
1
+ V
R6
= 2.75V + 2.25V = 5V
I
R7
= V
2
/R7 = 5V/10kΩ = 500µA
I
R8
= I
R7
+ I
R6
= 525µA
V
R8
= (V
nom
+10%) - V
2
= 13.2V - 5V = 8.2V Given: V
nom
= 12V
R8 = V
R8
/I
R8
= 8.2V/525µA = 15.62kΩ
Using the above resistor combination, a 12V output can be trimmed externally up to 13.2V and down to 10.8V. For further
information on external trimming, refer to Chapter 5 of the Applications Design Guide or consult the factory for assistance.
CONSULT APPLICATIONS ENGINEERING WHEN TRIMMING OUTPUTS BELOW 5V
Rev. 6/2004 Vicor 800-735-6200 Westcor Division 408-522-5280 Applications Engineering 800-927-9474 Pg. 17
PFC MegaPAC-EL/PFC MegaPAC-High Power Low Noise
(Remote Sense)
Load
+P +Out
J2-2 +Sense
J2-3 -Sense
-P -Out
Use 22-24 AWG Twisted Pa
ir Wires
R5
V
Ref
J2-1
R6
R8
R7
To Error
Amplifier
R4
R3
R2
R1
+
+
V
2
V1
-
-
RTH
Use 22-24 AWG
Twisted Pair Wires
Figure 11. External Trim