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TSS521: question about the additional mosfet

Expert 6280 points
Part Number: TSS521

Team,

Using the device per Figure 9 from the datasheet (Basic Optocoupler Application). C_STC  = 150uF, R_RIDD = 20kR.

In the datasheet, the example with Figure 6. (Basic Application Circuit With Support Capacitor C_STC > 50uF) adds a P-FET, BSS84 type, parallel between pin 3 and C_STC.

A few questions:

  1. What’s the function of BSS84 here?
  2. In which situations is it required?
  3. How does the presence of this FET influence the regeneration time (recovery to full communication ability) after a voltage drop (below 12V for longer than 0.1s)?

Thank you.

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