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Rev. 0.2 4/13 Copyright © 2013 by Silicon Laboratories AN520 AN520 CMOS A DVANCED G ALVANIC I SOLATORS FOR M EDICAL E LECTRONICS 1. Introduction Safety standards for ac line-powered medical electronic systems require galvanic isolation to protect patients and operators from electrically-induced trauma. The direct connection between machine and patient together with the presence of conductive body fluids and gels increase the risk of injury; therefore, isolators used in these systems must be robust and reliable. Optocouplers and transformers are commonly used within medical system isolation circuits, and their deficiencies are well known to the design community. Optocouplers are notoriously slow and exhibit wide performance variations over temperature and device lifetime. They are single-ended devices, which exhibit poor common-mode transient immunity (CMTI). In additi on, optocouplers are fabr icated in Gallium Arsenide (GaAs) processes with intrinsic wear-out mechanisms that cause permanent reduct ions in LED emission at elevated temperatures and/or LED currents. This degradatio n reduces optocoupler reliability, performance, and se rvice life. While transformers offer higher speed and better reliabilit y than optocouplers, they cannot pass dc and low-frequency signals, thus imposing limits on system timing (e.g ., ON-time and duty cycle). Transformers also tend to be large and power- inefficient and often require additional external components for core reset. 2. CMOS Isolator Overview Unlike optocouplers, complementary metal oxide semiconductor (CMOS) isolators offer substantial advantages in performance, reliability, operating stability, power savings, and functional in tegration. Unlike transformers, CMOS isolators operate from dc to 150 Mbps, require less space (up to six isolation channels per package), and are more power-efficient. These advantages are made possible by the following fundamental technologies underlying CMOS isolators.  Standard CMOS Process Technology Silicon Dioxide Based Capacitive Isolation Barrier instead of GaAs Process Technology CMOS is a well understood process technology with 40+ years of learning and offers 5.5 times lower failures-in- time (FIT) rate than GaAs-based optocouplers. The silicon dioxide isolation barrier offers a time dependent dielectric breakdown (TDDB) of 60 years compared to less than 15 years in optocouplers. It also offers a mean time-to-failure (MTTF) of 87 years. The operating temperature range is –40 to +125 °C as compared to –40 to +85 °C for optocouplers. This wide operating temperature range leads to greater parametric stability over voltage and temperature, and lower operating power versus optocouplers.  Improved Performance  Shorter propagation delay time and PWD, wider operating temperature range and greater parametric operating permit greater system stability than when using optocouplers.  High Frequency Carrier instead of Light RF technology further reduces isolator operating power and adds the benefits of precise frequency discrimination for superior noise rejection. Device packaging is also simpler compared to optocouplers.  Fully Differential instead of Single-Ended Isolation Path The differential signal path and high receiver selectivity enable CMTI above 25 kV/µs, excellent external RF field immunity to 300 V/m, and magnetic field immunity greater than 1000 A/m for error-free operation. These attributes make CMOS isolators well-suited for deployment in harsh operating environments where strong electric and magnetic fields are present, such as in motor-control circuits and medical MRI systems.  Proprietary EMI Suppression Techniques CMOS isolators meet the emission standards of FCC Part B and are tested to automotive J1750 (CISPR) test standards. For more information on CMOS isolators emissions, susceptibility, and reliability vs. optocouplers, see the Silicon Laboratories website at www.silabs.com/isolation.

From a system point of view, medical equipment is divided into individual classes according to operating voltage. Extra Low Voltage (SELV). Class III equipment does not require isolation. and clearance is the shortest path through air that an arc may travel. Figure 1. Creepage and Clearance Distances The heart of the isolator is the insulator, the dielectric strength of which determines the isolator's voltage rating. of its failsafe protection attribute. and clearance limits and stress voltage and duration as summarized in Table 1. Table 1. IEC60601-1 Safety Standard Requirements for CMOS Isolators

mechanical distance specification referred to as “Dist ance Through Insulation” (DTI), referenced in IEC 60601-1. uniformity than package mold compounds and, therefore, occupy less space. methodology standard). Limits for emissions and power line sensitivities are specified in IEC 60601-1-2. Table 2. IEC 60601-1-2 Immunity Requirements Note: Variable U is the ac mains voltage prior to the application of the test level. Table 1. IEC60601-1 Safety Standard Requirements for CMOS Isolators (Continued)

Table 4 is a summary of Silicon Laboratories isolation products compliant to medical specification IEC 60601. Table 3. Example Applications for CMOS Isolation Products in Medical Systems Table 4. Silicon Laboratories Isolation Products Summary* *Note: 8 mm creepage and clearance assumes conformal coating is used. Creepage in air is 7.6 mm.

8 Rev. 0.2 5. Summary Electronic medical systems must have robust integrated isolation to ensure patient and operator safety. Stringent international safety regulato ry agencies certify medical electronics systems to their specifications for uniform safety. Isolators play a key role in these systems and mu st be robust and reliable while requiring minimum space and adding negligible cost to the system. Optocouplers and transformers have been the preferred solutions for medical system isolator circuits. However, advances in technology have made possible smaller, more reliable, and higher-performance isolation devices including single-package multi-channel digital isolators, ac current sensors, and gate drivers. These new isolation products are base d on mainstream CMOS process technology. CMOS is a well understood process technology with 40+ years of learning and offers 5.5 times lower failures-in-time (FIT) rate than GaAs-based optocouplers. CMOS isolation products are the ideal solution for many electronic medical systems. When comb ined with Silicon Laboratories mixed-signal MCUs, ISOdrivers , and Si85xx-series current sensors, CMOS isolators enable highly-integrated, po wer-efficient designs that comply with critical safety specifications for medical systems.

Rev. 0.2 9 NOTES:

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 world’s 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.

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