KMP_78250C_C02 Page 1 of 3

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78250 Series

MAX250 Compatible Converter Transformers

For full details go to

www.murata-ps.com/rohs

　

FEATURES

RoHS compliant

Maxim MAX250 compatible

Isolation to 4kVrms

Industry-standard pinout

Surface mount option

UL 94 V-0 package materials

Low profile

Toroidal construction

Fully encapsulated

Industrial temperature range

DESCRIPTION

The 78250 series of converter transformers

are specifically designed for use with Maxim

chipsets to provide isolated RS232 interfaces.

Carefully controlled turns ratios ensure consistent

performance whilst a toroidal construction

minimises EMI.

CHARACTERISTICS 78250C/78250MC

Parameter

Conditions

Min.

Typ.

Max.

Units

Primary Inductance, L

P

10kHz, 100mV

1.0

2.0

2.5

mH

Leakage Inductance, L

L

100kHz, 100mV

2.0

3.0

μH

Interwinding Capacitance, C

WW

100kHz, 100mV

69

90

pF

Primary D.C. Resistance, R

DC

<0.1VDC

1.0

2.0

Ω

Volt-time Product, Et

Pins1/2 or 2/3

50

Vμs

CHARACTERISTICS 78250VC/78250MVC

Parameter

Conditions

Min.

Typ.

Max.

Units

Primary Inductance, L

P

10kHz, 100mV

1.0

2.0

2.5

mH

Leakage Inductance, L

L

100kHz, 100mV

35

40

μH

Interwinding Capacitance, C

WW

100kHz, 100mV

9

12

pF

Primary D.C. Resistance, R

DC

<0.1VDC

1.4

1.8

Ω

Volt-time Product, Et

Pins1/2 or 2/3

50

Vμs

ORDER CODE DETAILS

Order Code

Package Type

Packaging Type

Quantity

78250C / 78250VC

6 Pin DIL

Tube

50

78250MC / 78250MVC

6 Pin SM

Tube

50

78250MC-R / 78250MVC-R

6 Pin SM

Tape & Reel

500

ABSOLUTE MAXIMUM RATINGS

Operating free air temperature range

-40°C to 85°C

Storage temperature range

-50°C to 125°C

Lead temperature 1.5mm from case for 10 seconds

300°C

Peak current, I

PK

300mA

Isolation voltage 78250(M)C (flash tested for 1 second)

1.5kVrms

Isolation voltage 78250V(M)C (flash tested for 1 second)

4.0kVrms

All specifications typical at T

A

=25°C

TECHNICAL NOTES

ISOLATION

VOLTAGE

‘Hi Pot Test’, ‘Flash Tested’, ‘Withstand Voltage’, ‘Proof Volt-

age’, ‘Dielectric Withstand Voltage’ & ‘Isolation Test Voltage’

are all terms that relate to the same thing, a test voltage,

applied for a specified time, across a component designed

to provide electrical isolation, to verify the integrity of that

isolation.

All products in this series are 100% production tested at

their stated isolation voltage.

A question commonly asked is, “What is the continuous

voltage that can be applied across the part in normal opera-

tion?”

For a part holding no specific agency approvals both input

and output should normally be maintained within SELV limits

i.e. less than 42.4V peak, or 60VDC. The isolation test volt-

age represents a measure of immunity to transient voltages

and the part should never be used as an element of a safety

isolation system. The part could be expected to function cor-

rectly with several hundred volts offset applied continuously

across the isolation barrier; but then the circuitry on both

sides of the barrier must be regarded as operating at an

unsafe voltage and further isolation/insulation systems must

form a barrier between these circuits and any user-acces-

sible circuitry according to safety standard requirements.

REPEATED HIGH-VOLTAGE ISOLATION TESTING

It is well known that repeated high-voltage isolation

testing of a barrier component can actually degrade

isolation capability, to a lesser or greater degree

depending on materials, construction and environ-

ment. This series has toroidal isolation transformers,

with no additional insulation between primary and

secondary windings of enameled wire. While parts

can be expected to withstand several times the

stated test voltage, the isolation capability does de-

pend on the wire insulation. Any material, including

this enamel (typically polyurethane) is susceptible

to eventual chemical degradation when subject to

very high applied voltages thus implying that the

number of tests should be strictly limited. We there-

fore strongly advise against repeated high voltage

isolation testing, but if it is absolutely required, that

the voltage be reduced by 20% from specified test

voltage.

This consideration equally applies to agency recog-

nized parts rated for better than functional isolation

where the wire enamel insulation is always supple-

mented by a further insulation system of physical

spacing or barriers.