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78250 Series
MAX250/MAX251 Compatible Converter Transformers
FEATURES RoHS compliant Maxim MAX250/MAX251 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.
Surface-mount parts
The surface-mount (M suffix) products are not recommended for new designs. For existing designs, however, Murata Power Solutions will continue to manufacture and fully support these parts. For recommended alternatives please refer to the 78250J Series datasheet.
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For full details go to www.murata-ps.com/rohs
CHARACTERISTICS 78250C/78250MC
Parameter
Conditions
Primary Inductance, LP Leakage Inductance, L
L
Interwinding Capacitance, C WW
Primary D.C. Resistance, R DC
Volt-time Product, Et
10kHz, 100mV 100kHz, 100mV 100kHz, 100mV <0.1VDC Pins1/2 or 2/3
Min.
Typ.
Max.
Units
1.0
2.0
2.5
mH
2.0
3.0
μH
69
90
pF
1.0
2.0
Ω
50
Vμs
CHARACTERISTICS 78250VC/78250MVC
Parameter
Conditions
Primary Inductance, L P
Leakage Inductance, L L
Interwinding Capacitance, C WW
Primary D.C. Resistance, R DC
Volt-time Product, Et
10kHz, 100mV 100kHz, 100mV 100kHz, 100mV <0.1VDC Pins1/2 or 2/3
Min.
Typ.
Max.
Units
1.0
2.0
2.5
mH
35
40
μH
9
12
pF
1.4
1.8
Ω
50
Vμs
ORDER CODE DETAILS Order Code
78250C / 78250VC 78250MC / 78250MVC 78250MC-R / 78250MVC-R
Package Type 6 Pin DIL 6 Pin SM 6 Pin SM
Packaging Type Tube Tube
Tape & Reel
Quantity 50 50 500
ABSOLUTE MAXIMUM RATINGS Operating free air temperature range Storage temperature range Lead temperature 1.5mm from case for 10 seconds Peak current, I
PK
Isolation voltage 78250(M)C (flash tested for 1 second) Isolation voltage 78250(M)VC (flash tested for 1 second)
-40°C to 85°C -50°C to 125°C 300°C 300mA 1.5kVrms 4.0kVrms
All specifications typical at T =25°C A
TECHNICAL NOTES
ISOLATION VOLTAGE
REPEATED HIGH-VOLTAGE ISOLATION TESTING
‘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 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 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 voltage 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 correctly 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-accessible circuitry according to safety standard requirements.
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 environment. 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 applied 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 recognised parts rated for better than functional isolation where the wire enamel insulation is always supplemented by a further insulation system of physical spacing or barriers.
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PACKAGE SPECIFICATIONS
MECHANICAL DIMENSIONS 6 Pin DIL
0.375 (9.52) MAX
0.354 (9.0) Max.
78250C
XYYWW
Primary Secondary
1
6
2
3
4
78250 Series
MAX250/MAX251 Compatible Converter Transformers
6 Pin SM
0.354 (9.0) Max.
0.5 (12.70) 0.375 (9.52) Max.
78250MC
XYYWW
Primary Se.