SI8220 Datasheet, PDF (17/31 Pages) Silicon Laboratories – 0.5 AND 2.5 AMP ISODRIVERS WITH OPTO INPUT (2.5, 3.75, AND 5.0 KVRMS)

Si8220/21
C_{Lmax}
=
1---.--3---5-----_{----1---0----}^–_--³_{- – 1.85  10}–10
F
where:
C_{Lmax} is the maximum load (pF) allowable at switching frequency F
Equation 3.
A graph of Equation 3 is shown in Figure 13. Each point along the load line in this graph represents the package
dissipation-limited value of C_L for the corresponding switching frequency.
10,000
1,000
100
0
500
1,000
1,500
2,000
2,500
Frequency (KHz)
Figure 13. Maximum Load vs. Switching Frequency
6.4. Input Circuit Design
Opto driver manufacturers typically recommend the circuits shown in Figures 14 and 15. These circuits are
specifically designed to improve opto-coupler input common-mode rejection and increase noise immunity.
Vext
R1
OPTO DRIVER
1 N/C
2 ANODE
Control
Input
Open Drain or
Collector
3 CATHODE
4 N/C
Figure 14. Opto Driver Input Circuit
Rev. 1.5
17