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page

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DESCRIPTION:

DC/DC converter

3 of 3

08/2007

20050

phone 503.612.2300 fax 503.612.2382

PART NUMBER:

VASD2-SIP series

APPLICATION NOTES:

- Input filtering

To reduce the reflected ripple current and minimize EMI,

especially when the converter input is more than 2” away from

the DC source, it is recommended to connect a low ESR

electrolytic capacitor between Vin and Gnd. The values

suggested are as shown in Table 1. If additional filtering is

required, the capacitance may be increased, or expanded to

an LC network as shown in Figure 1.

Input Voltage

External Input Capacitance

4.7 µF

5 V

12 V

2.2 µF

24 V

1.0 µF

TABLE 1

Vout

External Ouput Capacitance

4.7 µF

5 V

9 V

2.2 µF

12 V

1.0 µF

15 V

0.47 µF

TABLE 2

<Figure 1>

+Vin

-Vin

+Vout

COM

DC

C

L

L

DC

L

C

C

-Vout

+Vin

-Vin

+Vin

-Vin

REG

+Vout

-Vout

COM

+Vout

DC

DC

DC

DC

REG

REG

COM

-Vout

REG

DC DC

DC DC

REG

REG

- Minimum loading

The converter needs a minimum of 10% loading to maintain

output regulation. Operation under no-load conditions will not

cause immediate damages but may reduce reliability, and

cause performance not to meet specifications.

- Regulation

With a semi-regulated design, the converter’s output voltage

varies with load current and will change proportionally to the

input voltage. If regulated output is needed, an external

regulator can be used as shown in Figure 2.

- Protection

The converter has minimal protection against input over-

voltage or output over-load, and may be permanently damaged

if exposed to these conditions. An input clamping device can

be used for input voltage limiting. An input fuse or an output

fuse also be used to protect against over-loading.

- Dual outputs used as a single output

The +Vout and -Vout can be used to obtain a single output

that is the sum of the two outputs. In this case, the COM pin

shouldn’t be used.

- External Regulator

An external 3-terminal regulator can be connected to the

output of the converter to achieve full regulation. Make sure

the converter’s output voltage provides sufficient head room

for the regulator. An additional benefit is that the built-in

protection features in the regulator, such as OCP, OTP, etc,

will protect the converter also. In a complimentory supply, a

negative output regulator must be used to achieve the

negative regulated output.

- Output filtering

An output capacitor is needed to meet output ripple

requirements as shown in Table 2.Output capacitance may be

increased for additional filtering, but should not exeed 10µF or

expanded to an LC network as in Figure 1.