rev. 0.2 4/13 copyright ? 2013 by silicon laboratories AN731 AN731 r eplacing t raditional o pto -d rivers with the si826 x d river f amily 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, swit ch-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 designer s to compromise circuit performance and/or add external components. until recently, replacing a legacy opto-drive r 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-drive r replacements that retrofit opto-driver sockets without pcb modification and provide significant gains in performance and reliability. this application no te examines these twenty-first century opto-driver upgrades. 2. si826x operation the input-side diod e emulator mimics the behavior of an opto-driver led to ensu re 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 th e 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. figure 1. si826x 4 and 6-pin block diagrams si826x ? isolated ? gate ? driver anode cathode v dd vo gnd e en xmit isolation isolation v ddi gndi recv r f 30v dc (max) v dd gnd v f nc si826x ? isolated ? gate ? driver anode nc cathode nc vo v dd vo gnd e en xmit isolation isolation v ddi gndi recv r f 30v dc (max) v dd gnd v f led ? emulator led ? emulator i f i f
AN731 2 rev. 0.2 this architecture provides numero us advantages over opto-drivers: ?? pin and package drop-in opto-coupler upgrade faster propagation time an d better parametric stab ility over voltage and temp erature compar ed to opto- drivers. ?? standard cmos process technology cmos is a well-understood process technology with 40+ years of development and offers 5.5 times lower fit rate (failures-in-time) than legacy opto-drivers as well as an expanded operating temperature range of C40 to +125 c (compared to C40 to +85 c for opto-dr ivers). the si826x isolation barrier lifetime is 10 times higher than that of opto-drivers. part-to-part matching is 14 times tight er than the gallium arsenide (gaas) process technologies used by opto-drivers. ?? precise current thresholds with hysteresis the si826x output is either low or high, with none of the ambiguous output states found in opto-drivers, and excellent threshold stability over voltage a nd temperature. ?? improved performance faster and more precise timing, lo wer-power operation, hi gher reliability, reduced internal parasitic coupling for better cmti, and gr eater parametric stability over temperature than opto-drivers. ?? silicon dioxide based capacitive isolation barrier silicon dioxide is an ultra-stable ma terial enabling an unparalleled lifetim e of over 60 years, compared to less than 15 years for the mold compound and polyimide tape used in opto-drivers. ?? superior surge tolerance withstands 10 kv surge per iec 60065. ?? wide product range the si826x digital isolators are available in so ic-8, dip8, lga8, and sdip6 packages. (for more information, see the si826x is olated driver data sheet.)
AN731 rev. 0.2 3 3. applications 3.1. replacing an existing opto-driver with the si826x ?? use the si826x data sheet or online guide to select the correct pin- and package-compatible si826x version for the end application. ?? desolder and discard the existing opto-driver from the board. ?? solder the selected si826x device into the si te previously occupied by the opto-driver. ?? if necessary, adjust the value of r f to achieve a maximum anode current of 6 ma. ?? connect power and verify proper system operation. note that the si826x is compatible with typical opto-d river circuits commonly used to improve opto-driver cmti performance (typical components include shorting switch es and reverse diode clamps). components of this type can be left in place or removed at the user's option. 4. evaluation board the si826x package and pin-compatibilit y make upgrading existing opto-drive r circuits quick and easy. simply look-up the closest replacement to the incumbent opto-drive r and replace it with th e si826x. the evb shown in figure 2 exercises the si826xa or b is olated gate driver and competing opto-driver simultaneously. an external digital input signal is buffered by an onboard driver and f ed into the inputs of both devices while the output signals are observed on an oscilloscope. figure 3 shows the output s of both devices at 25 c , while figure 4 shows the outputs at 85 c. note the faster propagation delay rise times provided by the si826x. figure 2. si826x isolated gate driver vs. opto-driver comparison board ?
AN731 4 rev. 0.2 figure 4 uses the same set up as figure 2 but, operating at an elev ated temperature of 85 c. the channel 1 waveform is the si826x output, and the channel 2 wavefo rm is the hcpl-4506 output. as operating temperature increases, the hcpl 4506 output falling edge is substant ially slower, and the propagation delay worsens compared to figure 3. note that the si826x output performa nce is essentially the same, as shown in figure 3. figure 3. propagation delays at 25 c figure 4. propagation delays at 85 c ? ? ? ?
AN731 rev. 0.2 5 5. summary the si826x isolated gate driver upgrad e is the first and only enhanced opto -driver replacement technology. this device family offers higher perfo rmance and grea ter reliability and ease-of-use t han legacy opto-drivers. the si826x easily retrofits into existing opto-driver sites and requires no pcb changes. these devices are ideal for retrofit or new designs.
AN731 6 rev. 0.2 d ocument c hange l ist revision 0.1 to revision 0.2 ? extensive rewrite of document.
AN731 rev. 0.2 7 n otes :
disclaimer silicon laboratories intends to provide customers with the latest, accurate, and in-depth documentation of all peripherals and modules available for system and software implementers using or intending to use the silicon laboratories products. characterization data, available modules and peripherals, memory sizes and memory addresses refer to each specific device, and "typical" parameters provided can and do vary in different applications. application examples described herein are for illustrative purposes only. silicon laboratories reserves the right to make changes without further notice and limitation to product information, specifications, and descriptions herein, and does not give warranties as to the accuracy or completeness of the included information. silicon laboratories shall have no liability for the consequences of use of the information supplied herein. this document does not imply or express copyright licenses granted hereunder to design or fabricate any integrated circuits. the products must not be used within any life support system without the specific written consent of silicon laboratories. a "life support system" is any product or system intended to support or sustain life and/or health, which, if it fails, can be reasonably expected to result in significant personal injury or death. silicon laboratories products are generally not intended for military applications. silicon laboratories products shall under no circumstances be used in weapons of mass destruction including (but not limited to) nuclear , biological or chemical weapons, or missiles capable of delivering such weapons. trademark information silicon laboratories inc., silicon laboratories, silicon labs, silabs and the silicon labs logo, cmems?, efm, efm32, efr, energy micro, energy micro logo and combinations thereof, "the worlds most energy friendly microcontrollers", ember?, ezlink?, ezmac?, ezradio?, ezradiopro?, dspll?, isomodem ?, precision32?, proslic?, siphy?, usbxpress? and others are trademarks or registered trademarks of silicon laboratories inc. arm, cortex, cortex-m3 and thumb are trademarks or registered trademarks of arm holdings. keil is a registered trademark of arm limited. all other products or brand names mentioned herein are trademarks of their respective holders. http://www.silabs.com silicon laboratories inc. 400 west cesar chavez austin, tx 78701 usa smart. connected. energy-friendly products www.silabs.com/products quality www.silabs.com/quality support and community community.silabs.com
|
