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2 Rev. 0.1 This simple architecture provides numerous advantages over optocouplers: Pin and Package Drop-In Opto-Coupler Upgrade Faster propagation time, better parametric stability over voltage and temperature, 2x to 3x lower internal parasitic coupling compared to optocouplers. Standard CMOS Process Technology CMOS is a well understood process technology with 40+ years of learning and offers 5.5 times lower failures-in-time (FIT) rate than GaAs-based optocouplers, a time dependent dielectric breakdown (TDDB) of 60 years, and a mean time-to-failure (MTTF) of 87 years. CMOS also provides an operating temperature range of –40 to +125 °C compared to –40 to +85 °C for optocouplers, greater parametric stability over voltage and temperature, and lower operating power versus optocouplers. Precise Current Thresholds with Hysteresis The Si826x output is either low or high, with no ambiguous output states and excellent threshold stability over voltage and temperature. There are no current transfer ratio (CTR) issues to address. Improved Performance Shorter propagation delay time and PWD, wider operating temperature range, and greater parametric operating stability than optocouplers. Silicon Dioxide Based Capacitive Isolation Barrier Silicon dioxide is an ultra-stable material enabling an unparalleled lifetime of over 60 years, compared to less than 15 years in optocouplers. Superior Surge Tolerance Withstands 10 kV surge per IEC 60065 Wide Product Range The Si87xx digital isolators are available in gull-wing PDIP8, SOIC8, LGA8, and SDIP6 packages and offer optional internal pull-up resistor and external enable. (For more information, see the Si87xx Digital isolator data sheet.)
Rev. 0.1 3 3. Applications 3.1. Replacing an Existing Optocoupler with the Si87xx Use the Si87xx data sheet or online guide to select the correct, pin-compatible Si87xx product for the application at hand. Desolder the existing optocoupler from the board and discard it. Solder the selected Si87xx device into the site previously occupied by the optocoupler. Adjust the value of RF to achieve a maximum current of 3 mA for the Si87xx A-grade and Si87xx C-grade devices or 6 mA for the B-Grade device (see Equation 1 below). Connect power and verify proper system operation. Note that the Si87xx is also compatible with typical ex ternal devices that improve optocoupler CMTI performance, such as shorting switches, reverse diode clamps, and ot hers. Components of this type can be left in place or removed at the user's option. 3.2. Using the Si87xx in New Designs Typically, the only calculated value is that of the current limiting resistor, R F. The first step is deciding if the application benefits more from low anode current (A-Grade or C-Grade) or from high common-mode transient immunity (B-Grade). Once this decision is made and the anode current threshold and optimum ON current values are known, values for calculating RF (see Equation 1) are straightforward. Equation 1. Note that it is best to keep the values of both V F and RF low because this offers greater resistance against CMT events. For example, a B-Grade Si87xx with V F = 5 V and RF =8 3 3 exhibits higher CMTI than the same device with VF = 10 V and RF =1 . 6k. RF VF 2.0– IF Where: RF is the value of the anode current limit resistor ( VF is the input-side forward voltage (V) IF is the Anode forward input current (mA)
6 Rev. 0.1 5. Summary The Si87xx digital optocoupler upgrade is the first and only enhanced optocoupler replacement technology available. This device family offe rs higher performance, greater reliability, increas ed ease-of-use, and more intuitive design than traditional optocouplers. The Si87xx easily retrofits into existi ng optocoupler circuits and requires no PCB changes. These devices are ideal for retrofit or new designs.
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8 Rev. 0.1 CONTACT INFORMATION Silicon Laboratories Inc.
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