Delta Electronics Series S48SP - Manual (Page 9)

DS_S48SP3R310_05222008 9
FEATURES DESCRIPTIONS (CON.)
Output Voltage Adjustment
To increase or decrease the output voltage set point,
the modules may be connected with an external
resistor between the TRIM pin and either the Vo(+) or
Vo(-). The TRIM pin should be left open if this feature
is not used.
R
Load
Vo (+)
Trim
Vo (-)
R
trim-down
Vi (+)
Vi (-)
ON/OFF
R
Load
Vo (+)
Trim
Vo (-)
R
trim-down
Vi (+)
Vi (-)
ON/OFF
Vo (+)
Trim
Vo (-)
R
trim-down
Vi (+)
Vi (-)
ON/OFF
Figure 17:
Circuit configuration for trim-down (decrease
output voltage)
If the external resistor is connected between the TRIM
and Vo(+) pins, the output voltage set point decreases
(Fig. 17). The external resistor value required to obtain
an output voltage change from 3.3V to the desired
Vo_adj is defined as:
Rtrim_down
Vo_adj 2.5
−
( ) 5110
⋅
3.3 Vo_adj
−
2050
−
Ex. When Trim-down -10%
Vo_adj=3.3V×(1-10%)=2.97V
Rtrim_down
2.97 2.5
−
( ) 5110
⋅
3.3 2.97
−
2050
−
Rtrim_down 5.228 10
3 × =
ohm
Vo (+)
Trim
Vo (-)
R
Load
R
trim-up
Vi (+)
Vi (-)
ON/OFF
Vo (+)
Trim
Vo (-)
R
Load
R
trim-up
Vi (+)
Vi (-)
ON/OFF
Figure 18: Circuit configuration for trim-up (increase output
voltage)
If the external resistor is connected between the TRIM
and Vo(-) the output voltage set point increases (Fig.
18). The external resistor value required to obtain an
output voltage change from 3.3V to the desired Vo_adj
is defined as:
Rtrim_up
2.5 5110
⋅
Vo_adj 3.3
−
2050
−
Ex. When Trim-up +10%
Vo_adj=3.3V×(1+10%)=3.63V
Rtrim_up
2.5 5110
⋅
3.63 3.3
−
2050
−
Rtrim_up 3.666 10
4
× =
ohm
When using trim function, the output voltage of the
module is usually increased, which increases the power
output of the module with the same output current.
Care should be taken to ensure that the maximum
output power of the module remains at or below the
maximum rated power.