Silicon Laboratories SI2493/57/34/15/04, SI2494/39 manual Safety, Surges

AN93

10.4.2. Safety

Designs using the ISOmodem pass all overcurrent and overvoltage tests for UL1950 3rd Edition with the addition of a 1.25 A Fuse or PTC, as shown in Figure 48. In a cost-optimized design, compliance to UL1950 does not always require overvoltage tests. In the design cycle, it is important to plan ahead and know which overvoltage tests will apply. System-level elements in the construction, such as fire enclosure or spacing requirements, need to be considered during the design stages. Consult with a testing agency during product design to determine which tests will apply.

1000 Ω @ 100 MHz, 200 mA

C8

FB1

RV1

1000 Ω @ 100 MHz, 200 mA

FB2

C9

1.25 A

TIP Fuse/PTC

RING

Figure 48. Circuits that Pass All UL1950 Overvoltage Tests

10.4.3. Surges

Use the reference design described in "4. Hardware Design Reference" on page 43 with through-hole Y1 capacitors for C1, C2, C8, and C9. Use spacing between the capacitor leads, between any line-side (high voltage) component or trace and system side (low voltage) component or trace greater than 8 mm. Also, the spacing between any line-side component or trace (or through-hole lead extending through the PCB) and the chassis (or anything connected to the chassis or low voltage circuitry) must be greater than 8 mm or protected with insulating material capable of withstanding a voltage greater than 8 kV. Additionally, slots cut through the PCB are recommended between the leads of C1, C2, C8, and C9 for increased creepage. The PCB and components should be clean and free of contamination, such as solder flux or other residue. The design engineer must verify the spacing indicated above meets or exceeds any specifications with which they wish to comply. The ISOmodem, used with the components and techniques described above, offers the highest reliability and lowest cost of any available solution. The use of supplemental surge-suppression components is not recommended.

254 Rev. 1.3