Output Voltage Trim - TDK-Lambda CPFE500 Application Note

OUTPUT VOLTAGE TRIM

Output voltage can be adjusted within the normal range by connecting a resistance or applying external voltage
to the TRIM terminal (J2,J3 pin 8)
Take care not to exceed the normal voltage adjustment range as Overvoltage protection (OVP) may activate
and shutdown the PSU.
When increasing or decreasing the output voltage, observe the PSU maximum output power and current.
If required, remote sense can be used in conjunction with the output voltage trim function.
Internally, the TRIM terminal is connected to the voltage reference of the output voltage control amplifier – see
figure 1 below :-
Figure 1 – CPFE500 TRIM terminal Internal Circuit
The output voltage can be decreased from the adjusted set-point by connecting an external resistance between
TRIM and –S.
Do not connect external resistance between TRIM and +S, this will cause output instability.
Alternatively the trim terminal maybe driven by an external voltage, see figure 2 below.
Typically when left unconnected, the TRIM terminal voltage is 0.75V.
When applying an external voltage to the TRIM terminal, the main output voltage follows the formula :-
VOUT = VOUT x (V
NOM
Figure 2 – Adjusting the output voltage using an external voltage source
CPFE500F Application Note
/ 0.75)
TRIM
(where VOUT is the output voltage setting with
NOM
TRIM terminal unconnected)
Document Number : 61066 iss 2 Page 4 of 17