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LTM8068

8068fb

For more information www.linear.com/LTM8068

LTM8068 Table 1b. Recommended Component Values and Configuration for Specific VOUT2 Voltages (TA = 25°C)

VIN

VOUT1

VOUT2

CIN

COUT1

COUT2

RFB1

RFB2

2.8V to 40V

1.7V

1.2V

2.2µF, 50V, 1206

100µF, 6.3V, 1210

10µF, 6.3V, 1206

20.5k

open

2.8V to 40V

1.5V

2.2µF, 50V, 1206

100µF, 6.3V, 1210

10µF, 6.3V, 1206

18.2k

2.32M

2.8V to 40V

2.4V

1.8V

2.2µF, 50V, 1206

100µF, 6.3V, 1210

10µF, 6.3V, 1206

15.8k

1.07M

2.8V to 40V

3.1V

2.5V

2.2µF, 50V, 1206

100µF, 6.3V, 1210

10µF, 6.3V, 1206

12.7k

487k

2.8V to 40V

3.9V

3.3V

2.2µF, 50V, 1206

47µF, 6.3V, 1210

10µF, 6.3V, 1206

10.5k

294k

2.8V to 38V

5.6V

2.2µF, 50V, 1206

22µF, 16V, 1210

10µF, 6.3V, 1206

7.32k

162k

2.8V to 36V

8.6V

2.2µF, 50V, 1206

22µF, 16V, 1210

10µF, 10V, 1206

4.89k

88.7k

2.8V to 32V

12.7V

12V

4.7µF, 50V, 1206

10µF, 50V, 1210

22µF, 16V, 1206

3.32k

56.2k

2.8V to 29V

15.8V

15V

4.7µF, 50V, 1206

4.7µF, 25V, 1210

22µF, 16V, 1206

2.67k

44.2k

2.8V to 26V

18.8V

18V

4.7µF, 50V, 1206

4.7µF, 25V, 1210

22µF, 25V, 1206

2.26k

36.5k

Note: An input bulk capacitor is required.

APPLICATIONS INFORMATION

Isolation, Working Voltage and Safety Compliance

The LTM8068 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 LTM8068 component.

The isolation rating of the LTM8068 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

requirements such as the gap between copper planes,

traces and component pins on the printed circuit board, as

well as the type of connector that may be used. To maxi-

mize the allowable working voltage, the LTM8068 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 0.78mm. 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 3.03mm. 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 LTM8068 internal circuitry is

required, the minimum metal to metal separation of the

primary and secondary is 0.75mm.

To reiterate, the manufacturer’s isolation voltage rating

and the required working or operational voltage are often

different numbers. In the case of the LTM8068, the iso-

lation voltage rating is established by 100% hi-pot test-

ing. 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 LTM8068 is a UL recognized component under

UL 60950, file number E464570. The UL 60950 insula-

tion category of the LTM8068 transformer is Functional.

Considering UL 60950 Table 2N and the gap distances

stated above, 3.03mm external and 0.75mm internal,

the LTM8068 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 LTM8068 is suitable for the intended application.

VOUT2 Post Regulator

VOUT2 is produced by a high performance low dropout

300mA regulator. At full load, its dropout is less than

430mV. Its output is set by applying a resistor from the

RFB2 pin to GND; the value of RFB2 can be calculated by

the equation:

RFB2 =

608.78

VOUT2 –1.22

kΩ

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