AN901 Datasheet, PDF (1/25 Pages) STMicroelectronics – Electromagnetic compatibility

AN901
DESIGN GUIDE FOR ISOLATED DC/DC USING THE SI884XX/886XX
1. Introduction
The Si884xx/Si886xx product families integrate digital isolator channels with an isolated dc-dc controller. This
application note provides guidance for selecting external components necessary for the operation of the dc-dc
controller.
Digital isolation applications with primary side supply voltage V_IN > 5.5 V or load power requirements of >2 W can
use Si884xx/Si886xx products. These product’s dc-dc controller uses the isolated flyback circuit topology. The
advantage of this topology when compared with the Si882xx/Si883xx is that it can be tailored to work in higher
voltage and higher power applications.
Figure 1 shows the minimum external components required for the isolated flyback, including optional support
circuitry. The components shown in Figure 1 are input capacitor C2, transformer T1, power switching FET Q1,
current sense resistor R12, primary snubber R16 and C19, secondary diode D1, output capacitor C10, secondary
snubber R8 and C8, voltage sense resistors R5 and R6, and compensation network components R7 and C11. Q2,
R14, and C14 create a regulator circuit to power VDDA from V_IN. C6 and R13 set the switching frequency and soft
start characteristics for product variants that use external frequency and soft start control.
Rev. 0.1 7/15
Figure 1. Required External Components
Copyright © 2015 by Silicon Laboratories
AN901