CONTROL FUNCTIONS - SC PIN
Output Voltage Programming
The output voltage of the converter can be adjusted or
programmed via fixed resistors, potentiometers or voltage
DACs. See Figures 7 & 8.
+Out
+Out
R
U
Trim Up
Error
Amp
1kΩ
0.033µF
SC
R
D
Trim Down
Load
Error
Amp
1kΩ
0.033µF
SC
Load
–Out
1.23V
1.23V
–Out
R
D
(ohms) =
1,000 Vout
Vnom - Vout
R
U
(ohms) =
1,000
(Vout-1.23)
Vnom
1.23
(Vout-Vnom)
- 1,000
Figure 7—Output
voltage trim down circuit.
Trim Down
1. This converter is not a constant power device – it has a
constant current limit. Hence, available output power is
reduced by the same percentage that output voltage is
trimmed down. Do not exceed maximum rated output current.
2. The trim down resistor must be connected to the –Out pin.
Figure 8—Output
voltage trim up circuit.
Trim Up
1. The converter is rated for a maximum delivered power. To ensure
that maximum rated power is not exceeded, reduce maximum
output current by the same percentage increase in output voltage.
2. The trim up resistor must be connected to the +Out pin.
3. Do not trim the converter above maximum trim range
(typically +10%) or the output over voltage
protection circuitry may be activated.
Trim values calculated automatically:
Resistor trim calculators are available on Vicor’s
web site at URL: www.vicr.com/tools.html
or by requesting a copy of Vicor’s
Applications Manual on a CD ROM.
Resistor values can be calculated for fixed
trim up, fixed trim down and for variable
trim up or down cases for both 1st and
2nd Generation DC-DC converters.
In addition to trimming information, the
web site and the applications manual on
CD ROM also include design tips,
applications circuits, EMC suggestions,
thermal design guidelines and PDF data
sheets for all available Vicor products.
Vicor Corporation
Tel: 800-735-6200 Fax: 978-475-6715
Data Sheet: V24C28C100A DC-DC Converter Date: 11-00 Rev. 2
Page 5 of 8
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