cui.com

date 08/31/2021

│ page 5 of 6

CUI Inc

│ SERIES: VCD40 │ DESCRIPTION: DC-DC CONVERTER

Note:

All specifications measured at 25°C, nominal input voltage, and full load unless otherwise noted.

)

(K

)

1

(

,

Ω

Ω

Ω

-

-

x

=

-

Rt

V

Vo

Vr

R

R

nom

o

up

trim

1. The value of Rtrim-up defined as:

Where: R trim-up is the external resistor in Kohm.

Vo,nom is the nominal output voltage.

Vo is the desired output voltage.

R1 ,Rt and Vr are internal to the unit and are defined in Table 1.

For example, to trim-up the output voltage of 5.0V module

(VCD40-D48-S5) by 5% to 5.25V, R trim-up is calculated as follows:

Vo – Vo,nom = 5.25 – 5.0 = 0.25V

R1 = 2.32 Kohm

Rt = 8.2 Kohm , Vr= 2.5

)

(K

15

2

.

8

25

.

0

5

.

2

32

.

2

=

-

x

=

trim

R

The value of R trim-down defined as:

)

(K

)

(

1

,

-

-

-

x

=

-

Rt

Vo

V

Vr

Vo

R

R

nom

o

down

trim

Where: R trim-down is the external resistor in Kohm.

Vo,nom is the nominal output voltage.

Vo is the desired output voltage.

R1 ,Rt and Vr are internal to the unit and are defined in

Table 1.

For example, to trim-down the output voltage of 5.0V module

(VCD40-D48-S5) by 5% to 4.75V, R trim-down is calculated as follows :

Vo,nom – Vo = 5.0 – 4.75 = 0.25 V

R1 = 2.32 Kohm

R t = 8.2 Kohm , Vr=2.5

)

(K

68

.

12

2

.

8

25

.

0

)

5

.

2

75

.

4

(

32

.

2

=

-

-

x

=

trim

R

Ω

In order to trim the voltage up or down one needs to connect the trim resistor either between the trim pin and -Vo for trim-up and between trim

pin and +Vo for trim-down. The output voltage trim range is ±10%. This is shown in

Figures 1 and 2:

Model Number

Output Voltage(V)

R1 (Kohm)

R2 (Kohm)

R3 (Kohm)

Rt (Kohm)

Vr

3.3V

2.74

1.8

0.27

9.1

1.24

12V

6.8

2.4

2.32

22

2.5

15V

8.06

2.4

3.9

27

2.5

Table 1 - Trim Resistor Values

Model Number

Output Voltage(V)

R1 (Kohm)

Rt (Kohm)

Vr

Table 2 - Trim Resistor Values

VCD40-D24-S5

VCD40-D48-S5

5.02.328.2

2.5

VCD40-D24-S3R3

VCD40-D48-S3R3

VCD40-D24-S12

VCD40-D48-S12

VCD40-D24-S15

VCD40-D48-S15

2. The output Voltage 3.3V,12V and 15V value of Rtrim are

defined as below:

)

(K

)

2

)

(

)

3

2

(

1

(

,

-

x

-

+

x

x

=

-

Rt

R

V

Vo

R

R

R

Vr

R

nom

o

up

trim

)

(K

)

1

2

)

(

1

(

1

,

-

-

x

-

x

x

=

-

Rt

R

Vo

V

R

Vr

R

R

nom

o

down

trim

Where: R trim-up is the external resistor in Kohm.

Vo,nom is the nominal output voltage.

Vo is the desired output voltage.

R1, R2, R3, Rt and Vr are internal to the unit and are defined in

Table 2.

Ω

Ω

Figure 1

Figure 2

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