LTM8049 datasheet(12/20 Pages) LINER

12 / 20 page

LTM8067

8067fc

For more information www.linear.com/LTM8067

APPLICATIONS INFORMATION

Isolation, Working Voltage and Safety Compliance

The LTM8067 isolation is 100% hi-pot tested by tying

all of the primary pins together, all of the secondary pins

together and subjecting the two resultant circuits to a

high voltage differential for one second. This establishes

the isolation voltage rating of the LTM8067 component.

The isolation rating of the LTM8067 is not the same as

the working or operational voltage that the application

will experience. This is subject to the application’s power

source, operating conditions, the industry where the end

product is used and other factors that dictate design re-

quirementssuchasthegapbetweencopperplanes,traces

and component pins on the printed circuit board, as well

as the type of connector that may be used. To maximize

the allowable working voltage, the LTM8067 has two

columns of solder balls removed to facilitate the printed

circuit board design. The ball to ball pitch is 1.27mm, and

the typical ball diameter is 0.75mm. Accounting for the

missing columns and the ball diameter, the printed circuit

board may be designed for a metal-to-metal separation of

up to 3.06mm. This may have to be reduced somewhat to

allow for tolerances in solder mask or other printed circuit

board design rules. For those situations where informa-

tion about the spacing of LTM8067 internal circuitry is

required, the minimum metal to metal separation of the

primary and secondary is 1mm.

To reiterate, the manufacturer’s isolation voltage rating

and the required working or operational voltage are of-

ten different numbers. In the case of the LTM8067, the

isolation voltage rating is established by 100% hi-pot

testing. The working or operational voltage is a function

of the end product and its system level specifications. The

actual required operational voltage is often smaller than

the manufacturer’s isolation rating.

The LTM8067 is a UL recognized component under

UL 60950, file number 464570. The UL 60950 insula-

tion category of the LTM8067 transformer is Functional.

Considering UL 60950 Table 2N and the gap distances

stated above, 3.06mm external and 1mm internal, the

LTM8067 may be operated with up to 250V working

voltage in a pollution degree 2 environment. The actual

working voltage, insulation category, pollution degree and

other critical parameters for the specific end application

depend upon the actual environmental, application and

safety compliance requirements. It is therefore up to the

user to perform a safety and compliance review to ensure

that the LTM8067 is suitable for the intended application.

Safety Rated Capacitors

Some applications require safety rated capacitors, which

are high voltage capacitors that are specifically designed

and rated for AC operation and high voltage surges. These

capacitorsareoftencertifiedtosafetystandardssuchasUL

60950, IEC 60950 and others. In the case of the LTM8067,

a common application of a safety rated capacitor would

be to connect it from GND to VOUTN. To provide maximum

flexibility, the LTM8067 does not include any components

between GND and VOUTN. Any safety capacitors must be

added externally.

The specific capacitor and circuit configuration for any

application depends upon the safety requirements of

the system into which the LTM8067 is being designed.

Table 2 provides a list of possible capacitors and their

manufacturers. The application of a capacitor from GND

to VOUTN may also reduce the high frequency output noise

on the output.

Table 2. Safety Rated Capacitors

MANUFACTURER PART NUMBER

DESCRIPTION

Murata

Electronics

GA343DR7GD472KW01L

4700pF, 250V AC, X7R,

4.5mm × 3.2mm

Capacitor

Johanson

Dielectrics

302R29W471KV3E-****-SC 470pF, 250V AC, X7R,

4.5mm × 2mm

Capacitor

Syfer Technology 1808JA250102JCTSP

100pF, 250V AC, C0G,

1808 Capacitor

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