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 and 8.
+OUT
+OUT
R
U
Trim Up
Error
Amp
1 kΩ
0.033
μF
SC
R
D
Trim Down
Load
Error
Amp
1 kΩ
0.033
μF
SC
Load
–OUT
1.23 V
1.23 V
–OUT
R
D
(ohms) =
1,000 Vout
Vnom – Vout
R
U
(ohms) = 1,000 (Vout –1.23) Vnom – 1,000
1.23 (Vout – Vnom)
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 resistor values calculated automatically:
On-line calculators for trim resistor values are available
on the vicor website at:
Resistor values can be calculated for fixed trim up,
fixed trim down and for variable trim up or down.
In addition to trimming information, the web site and
the Applications Manual also include design tips,
applications circuits, EMC suggestions, thermal design
guidelines and PDF data sheets for all available Vicor
products.
Vicor Corp.
Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
48V Micro Family
Rev. 7.5
Page 9 of 13
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