AN441 Si8232/5/6 UL1577 Si8230/1/3/4

U SING T H E S i 8 2 3 2 / 5 / 6 D UAL I S O D R I V E R S IN P O W E R D E L I V E R Y S Y S T E M S 1. Introduction The

AN441 AN441 U SING T H E S i 8 2 3 2 / 5 / 6 D UAL I S O D R I V E R S IN P O W E R D E L I V E R Y S Y S T E M S 1. Introduction The Si8232/5/6 Si8232/5/6 are isolated dual 0.5 A and 4.0 A MOSFET/IGBT gate drivers based on Silicon Labs' proprietary CMOS isolation technology. These devices provide up to 5 kVRMS withstand voltage per UL1577 UL1577, and fast 60 ns propagation delay time. Their high integration, flexibility, and performance allow these drivers to be used in a number of circuit applications and are the focus of this application note. Unlike Silicon Labs' dedicated high-side/low-side ISOdrivers (Si8230/1/3/4 Si8230/1/3/4), the Si8232/5/6 Si8232/5/6 Dual ISOdrivers have no built-in overlap protection or dead time setting; so, the state of each driver output unconditionally follows that of its input as long as the device is powered. For more information on ISOdrivers, please see the Si823x datasheet. Figure 1. Si8232/5/6 Si8232/5/6 Block Diagram A block diagram of the Si8232/5/6 Si8232/5/6 Dual ISOdriver is shown in Figure 1. Each isolated driver output is controlled by its own input pin (VIA, VIB), both of which are gated by the input-side UVLO and DISABLE signals. The two driver output circuits are isolated from each other and from the input, allowing the common-mode voltage of one driver to reverse polarity with respect to the other without damage (i.e. latch-up) or output errors. Rev. 0.2 4/10 Copyright © 2010 by Silicon Laboratories AN441 AN441 AN441 AN441 For example, in a given application, GNDA might have a common-mode voltage of 100 V while GNDB has a common-mode voltage of 200 V. These two common-mode voltages can reverse (i.e. GNDA change to 200 V, and GNDB can change to 100 V as in Figure 2) without damaging or upsetting the driver. The Si8232/5/6 Si8232/5/6 drivers can, therefore, be used in dual-low-side, dual-high-side, or high-side/low-side configurations in systems where common-mode voltages vary greatly. VDDI VDDA Si8232/5/6 Si8232/5/6 VDDA GNDI OUT A GNDA GNDA From Controller VDDB VIA VDDB VIB OUT B VOB GNDB DISABLE VOB Output Signal VOA Output Signal VOA GNDB Common Mode Voltage (V) VDDI Common Mode Voltage V1 VOB Output Signal VOA Output Signal Common Mode Voltage V2 Time Figure 2. Common-Mode Voltage Inversion 2 Rev. 0.2 AN441 AN441 2. Application Examples 2.1. Increased Peak Output Current In many power applications, such as UPS systems and inverters, switches must be paralleled for the system to deliver rated power at high operating efficiencies. The combined capacitive loading of these switches requires either a higher peak current driver or a less desirable method of distributing the switches over multiple gate driver ICs. VDDA LOAD VDDI 5V Si8232/5/6 Si8232/5/6 VDDI VDDA VOA GNDA GNDI From Controller VIA VDDB GNDB VIB VOB DISABLE Figure 3. Paralleled Outputs for Increased Peak Output Current The circuit of Figure 3 shows each Si8232/5/6 Si8232/5/6 output driving several common ground switches in parallel. When connected in this way, the dual ISOdriver can provide an equivalent peak drive current of 8 A. Tight 60 ns propagation delay time (across the operating voltage and temperature range) ensures that all switches are driven off and on simultaneously. Rev. 0.2 3 AN441 AN441 2.2. Isolated Dual Buck Converter Power circuits in high-voltage systems, such as imaging systems and plasma flat panels, have split ground systems to isolate higher voltages from lower voltages. In many cases, local supply regulators are built using a dedicated controller for each regulator or, in other cases, a transformer-coupled multi-output design (using flyback or other transformer-coupled topology). These designs tend to consume excessive space and add cost. VDDA (24V) VDDI 5V HV Si8232/5/6 Si8232/5/6 VDDI VDDA VOA VOUT 1 GNDA GNDI VDDB (24V) TWO-LOOP CONTROLLER OUT1 LV VIA VDDB OUT2 VIB VOB GNDB I/O VFB1 VOUT 2 DISABLE ANALOG SIGNAL ISOLATION VFB2 Figure 4. Isolated Dual Buck Converter Figure 4 shows a dual output isolated buck converter using the Si8232/5/6 Si8232/5/6 dual ISOdriver. As shown, a single twoloop controller is used with the ISOdriver to generate two stepped-down output voltages. The ISOdriver operates as an isolated dual high-side driver where each output is isolated from both the adjacent output and from the primary side. While this circuit uses a low-cost Shottkey free-wheeling diode; a second dual ISOdriver can be added to control output synchronous rectifiers for higher efficiency. 4 Rev. 0.2 AN441 AN441 2.3. Synchronous Rectifier High-efficiency isolated power systems use output-side synchronous rectifier FETs instead of Shottkey diodes. These FETs are driven by isolated low-side gate drivers, usually implemented with combinations of gate drive transformers or optocouplers and non-isolated drivers. The resulting circuits tend to be bulky, inefficient, and slow. L1 C1 Cn VOUT Q1 T1 Q2 L2 PRIMARY (HV) VDDI 5V SECONDARY (LV) SYNCHRONOUS CURRENT DOUBLER Si8232/5/6 Si8232/5/6 VDDI VDDA VOA GNDA GNDI CONTROLLER OUT1 VIA OUT2 VIB VDDB VOB VDDA (24Vmax) GNDB I/O DISABLE Figure 5. Synchronous Rectifier Control As shown in Figure 5, the Si8232/5/6 Si8232/5/6 provides both primary/secondary side isolation and switch gate drive for the secondary-side synchronous current doubler. Even a simple optocoupler plus non-isolated driver plus passives can occupy nearly 130 square millimeters and have overall propagation times of more than 100 ns. By comparison, the Si8232/5/6 Si8232/5/6 is a single-chip solution for the isolated low-side driver required by this application. In addition, the Si8232/5/6 Si8232/5/6 offers over 50% faster propagation delays and occupies only 40% of the space required by the optocoupler solution when using the Si823x packaged in the 5 mm x 5 mm QFN. Rev. 0.2 5 AN441 AN441 3. Summary The Si8232/5/6 Si8232/5/6 Dual ISOdriver can be used as an isolated high-side/low-side, dual-high-side, or dual-low-side driver. Its high integration limits external BOM count to a maximum of four passive components. Its high commonmode rejection allows it to be used in high common-mode voltage environments without device damage or upset, even when the common-mode voltage excursions are severe. 6 Rev. 0.2 AN441 AN441 DOCUMENT CHANGE LIST Revision 0.1 to Revision 0.2 Updated title from "Using the Si8232/5/6 Si8232/5/6 Dual ISODrivers" to "Using the Si8232/5/6 Si8232/5/6 Dual ISODrivers in Power Deliver Systems". Rev. 0.2 7 AN441 AN441 CONTACT INFORMATION Silicon Laboratories Inc. 400 West Cesar Chavez Austin, Texas 78701 Tel: 1+(512) 416-8500 Fax: 1+(512) 416-9669 Toll Free: 1+(877) 444-3032 Please visit the Silicon Labs Technical Support web page: and register to submit a technical support request. The information in this document is believed to be accurate in all respects at the time of publication but is subject to change without notice. Silicon Laboratories assumes no responsibility for errors and omissions, and disclaims responsibility for any consequences resulting from the use of information included herein. Additionally, Silicon Laboratories assumes no responsibility for the functioning of undescribed features or parameters. Silicon Laboratories reserves the right to make changes without further notice. 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Silicon Laboratories and Silicon Labs are trademarks of Silicon Laboratories Inc. Other products or brandnames mentioned herein are trademarks or registered trademarks of their respective holders. 8 Rev. 0.2