AN731 Datasheet, PDF (1/8 Pages) Silicon Laboratories – REPLACING TRADITIONAL OPTO-DRIVERS

AN731
REPLACING TRADITIONAL OPTO-DRIVERS WITH THE
Si826X DRIVER FAMILY
1. Introduction
Optocoupler-based gate drivers (“opto-drivers”) have been around for decades and favored over other gate drive
solutions because they provide safety isolation and level shifting in a single package. Typical opto-driver
applications include motor and motion control, switch-mode power delivery, and test and medical systems.
Opto-drivers are, however, not without their problems; they exhibit weaknesses in critical areas making them less-
than-optimal for some applications and forcing designers to compromise circuit performance and/or add external
components. Until recently, replacing a legacy opto-driver with a modern CMOS isolated gate driver required
significant design and PCB changes that increased costs and design risks. The Si826x family changes this
dynamic by offering pin- and package-compatible opto-driver replacements that retrofit opto-driver sockets without
PCB modification and provide significant gains in performance and reliability. This application note examines these
twenty-first century opto-driver upgrades.
2. Si826x Operation
The input-side diode emulator mimics the behavior of an opto-driver LED to ensure compatibility with existing opto-
driver input circuits. The diode emulator enables the high-frequency transmitter when input current I_F is at or above
its threshold value, sending a high-frequency carrier across the isolation barrier to the receiver. This high-selectivity
receiver forces the output driver high when sufficient in-band energy is detected. Input current below the I_F
threshold disables the transmitter, causing the receiver to force the output driver low.
NC
IF _ANODE
RF
VF _CATHODE
NC
Si826x Isolated Gate Driver
VDDI
VDD
e EN XMIT
LED
Emulator
GNDI
RECV
GND
30VDC(max)
VDD
Vo
Vo
GND
IF ANODE
RF
VF
NC
CATHODE
Si826x Isolated Gate Driver
VDDI
VDD
e ^{EN XMIT}
LED
Emulator
GNDI
RECV
GND
30VDC(max)
VDD
Vo
GND
Rev. 0.2 4/13
Figure 1. Si826x 4 and 6-Pin Block Diagrams
Copyright © 2013 by Silicon Laboratories
AN731