 SMM4F Product
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The new SMM4F series of planar Transils can withstand a maximum junction temperature of 175 °C to meet the severe working conditions required by SMPS for portable equipment. Housed in the flat 3.8 x 1.9 mm STmite package, the new SMM4F Transil series is able to protect against 400 W 10/1000 μs surges, providing an excellent power capability / size ratio.
The SMM4F easily meets the IEC61000-4-5 surge and environmental requirements.
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The SMM4F is the first 400 W Transil series packaged in a flat STmite while one of our main competitors is proposing 200 W max in SMF or 400 W in SMA, cutting back on space saving or on efficiency.
Only ST can offer 400 W protection in such a small package
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Thanks to their ST Planar technology, maximum leakage currents have been decreased from 1 or 5 μA to 0.2 μA at 25 °C, and are now also specified at 1 μA max at 85 °C (telecom range).
Maximum junction temperature |
Requirements on maximum junction temperature depend on the final target application. Despite the fact that the ambient temperature range is often limited to -20 °C to + 70 °C in SMPS applications, it is by far the most stressful.
The SMM4F is specified at Tjmax = 175 °C to be 100% compatible with ST rectifiers already rated at 175 °C.
IEC61000-4-5 standard requires the surge capability to state the application is correctly protected.
IEC61000-4-2 specifies 8/20μs surges with various levels depending on environment and applications. Consequently the SMM4F series are specified with a maximum clamping voltage (VCL) at 8/20 μs as well as the usual 10/1000 μs. Temperature coefficient ( T) and dynamic resistance (RD) are also available, to calculate VCL max whatever surge and temperature are, together with the formula in the datasheet. Below is an example with a given maximum VCL for a system on a 12 V dataline working from -40 °C to 85 °C with a serial resistance of 6.8 Ω. A surge of 1 kV/42 Ω is applied, as per the IEC requirement.
SMM4F13A (VRM = 13 V)
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VBRmin
[V]
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VBRmax
[V]
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VCL
[V]
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VPP
[A] |
RD
[Ω] |
αT |
Datasheet
at 25 °C |
14.3 |
15.8 |
27.2 |
85 |
0.35 |
8.4 x 10-4 |
Value
at 25 °C |
14.3 |
15.8 |
22.8 |
20 |
- |
- |
Value
at 40 °C |
13.5 |
14.9
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21.9
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20 |
- |
- |
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15 |
16.6 |
23.6 |
20 |
- |
-
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VCL and VBR versus Tj and IPP
The option to obtain the exact VCL versus Tj and surge in the application allows the designer to be sure VCL is not higher than the maximum voltage of the integrated circuit to be protected. Also when the junction temperature is low, it is important to be sure VBR min is higher than the rated signal.
With a VRM voltage range from 5 to 33 V, it can fit most applications of any segment. The low leakage current (0.2 μA and 1 μA max respectively at 25 and 85 °C) make it suitable for portable equipment where power consumption is a key issue.
Developed according to RoHS standards, ST is going one step beyond with a halogen free molding compound. |
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