VICOR DC MegaPAC, User Manual

Page: 16 / 19

UG:123 Page 16
Output Module V
REF
R
TH
VI-200/VI-J00
≥
3.3V 2.50V 10.0k
Ω
VI-200/VI-J00 <3.3V 0.97V 3.88k
Ω
Example:
±10% Trim adjust on a 12V nominal output.
Figure 9 shows a typical variable Trim circuit. Using a 10k
Ω
trimpot (R7), the resistor values for R6 and
R8 can be calculated as follows:
V
1
= V
REF
+ 10% = 2.75V Given: V
REF
= 2.5V (see Table above)
I
R5
= (2.75V – V
REF
)/R
TH
= (2.75V - 2.5V) / 10k
Ω
= 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 = 90k
Ω
V
2
= V
1
+ V
R6
= 2.75V + 2.25V = 5V
I
R7
= V
2
/ R7 = 5V / 10k
Ω
= 500µA
I
R8
= I
R7
+ I
R6
= 525µA
V
R8
= (V
NOM
+ 10%) – V
2
= 13.2V – 5V = 8.2V Given: V
NOM
= 12V
R
8
= V
R8
/ I
R8
= 8.2V / 525µA = 15.62k
Ω
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 Manual or
consult the factory for assistance.
CONSULT APPLICATIONS ENGINEERING WHEN TRIMMING OUTPUTS BELOW 5V.
Figure 9
External Trim
(Remote Sense)
Load
+P +OUT
J2-2 +Sense
J2-3 –Sense
–P –OUT
Use 22-24AWG Twisted Pair Wires
R5
V
REF
J2-1
R6
R8
R7
To Error
Amplifier
R4
R3
R2
R1
+
+
V
2
V
1
-
-
R
TH
Use 22-24AWG
Twisted Pair Wires