Delta Electronics Q48SR - Manual (Page 10)

FEATURES DESCRIPTIONS (CON.)
Output Voltage Adjustment (TRIM)
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
SENSE(+) or SENSE(-). The TRIM pin should be left
open if this feature is not used.
Figure 20:
Circuit configuration for trim-up (increase output
voltage)
If the external resistor is connected between the TRIM
and SENSE (+) pins, the output voltage set point
increases (Fig. 24). The external resistor value
required to obtain a percentage of output voltage
change % is defined as:
( )
Ω − Ω
⎥
⎦
⎤
⎢
⎣
⎡
∆
− ∆ +
=
k k
ref
ref onom
11 10
V
V 1 V
) Rtrim_up(∆
where
Vonom = nominal Vout (3.3V or 1.8V)
Vref = 1.225V
∆ = trim expressed as decimal fraction, i.e. 10% is written
as 0.1
Ex. When trim up to 3.6V from 3.3V
Vonom = 3.3V
Vref = 1.225V
∆ = (3.6-3.3)/3.3 = 0.0909
⇒
( )
Ω = Ω −
Ω Ч
− Ч
= −
K K
K up Rtrim
283 . 202 11
10
0909 . 0 * 225 . 1
225 . 1 0909 . 1 3 . 3
Figure 21: Circuit configuration for trim-down (decrease
output voltage)
If the external resistor is connected between the TRIM
and SENSE (-) the output voltage set point decreases
(Fig. 21). The external resistor value required to obtain
a percentage output voltage change % is defined
as:
( )
Ω −
∆
ΚΩ
= ∆
k
11
10
Rtrim_down
where
Vonom = nominal Vout (3.3V or 1.8V)
∆ = trim expressed as decimal fraction, i.e. 40% is
written as 0.4
Ex. When trim down to 1.7V from 3.3V
Vonom = 3.3V
∆ = (3.3-1.7)/3.3 = 0.4848
Ω = Ω − = −
K K
K
down Rtrim
627 . 9 11
4848 . 0
10
The output voltage can be increased by both the remote
sense and the trim, however the maximum increase
allowed is the larger of either the remote sense spec or
the trim spec, not the sum of both.
When using remote sense and trim, 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.
Output voltage
Resistor value (
Ω
k
)
2.5V 30.25
2.0V 14.38
Figure 22:
Trim resistor value example for popular output
voltages. Connect the resistor between the TRIM and
SENSE (-) pins.
11