78250J Series

MAX250/MAX251 Compatible Converter SM Transformers

KMP_78250JC_A03 Page 1 of 3

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FEATURES

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RoHS compliant

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Maxim MAX250/MAX251 compatible

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Isolation to 4kVrms

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Industry-standard pinout

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Surface mount option

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UL 94 V-0 package materials

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Low profile

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Toroidal construction

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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.

For through hole versions see 78250 datasheet.

CHARACTERISTICS 78250JC

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

0.6

3.0

μH

Interwinding Capacitance, C

WW

100kHz, 100mV

48

90

pF

Primary D.C. Resistance, R

DC

<0.1VDC

0.7

2.0

Ω

Volt-time Product, Et

Pins1/2 or 2/3

50

Vμs

Turns Ratio

1:1

CHARACTERISTICS 78250JVC

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

4

10

pF

Primary D.C. Resistance, R

DC

<0.1VDC

0.9

1.8

Ω

Volt-time Product, Et

Pins1/2 or 2/3

50

Vμs

Turns Ratio

1:1

ORDER CODE DETAILS

Order Code

Package Type

Packaging Type

Quantity

78250JC / 78250JVC

6 Pin SM

Tube

50

78250JC-R / 78250JVC-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(J)C (flash tested for 1 second)

1.5kVrms

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

4.0kVrms

All specifications typical at T

TECHNICAL NOTES

ISOLATION

VOLTAGE

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

‘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 electri-

cal 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 volt-

age that can be applied across the part in normal operation?”

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-accessi-

ble 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 depend on

the wire insulation. Any material, including this enamel

(typically polyurethane) is susceptible to eventual

chemical degradation when subject to very high ap-

plied voltages thus implying that the number of tests

should be strictly limited. We therefore 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.