{"id":15553,"date":"2026-08-11T09:00:00","date_gmt":"2026-08-11T07:00:00","guid":{"rendered":"https:\/\/tps-elektronik.com\/?post_type=case_studies&#038;p=15553"},"modified":"2026-07-14T09:33:08","modified_gmt":"2026-07-14T07:33:08","slug":"how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters","status":"publish","type":"case_studies","link":"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/","title":{"rendered":"How to Pass Automotive Conducted Emissions CISPR 25 Class 5 with TPS Split Ground Plane and Common Mode Choke Placement \u2013 EMC Layout Guidelines for Automotive DC-DC Converters?"},"content":{"rendered":"<article class=\"blog-post\" lang=\"en\"><header>\n<p>A German automotive Tier 1 supplier faced a critical project milestone: their 48 V to 12 V DC-DC converter for an electric vehicle platform had to pass CISPR 25 Class 5 conducted emissions. The most stringent automotive EMI standard. Initial pre-compliance testing at TPS Elektronik&#8217;s EMC laboratory revealed excessive noise across the AM and FM broadcast bands, with peaks exceeding Class 5 limits by more than 10 dB\u03bcV. The root cause? A poorly implemented split ground plane and suboptimal common mode choke placement that turned the PCB into an unintentional antenna.<\/p>\n<p>This case study documents how our engineering team guided the customer through targeted layout modifications\u2014ground plane stitching, choke repositioning, and filter network optimization. Which to achieve CISPR 25 Class 5 compliance without a costly board respin. For system integrators, panel builders, and electrical engineers facing similar challenges, the lessons learned offer a practical roadmap for automotive EMC success with EMC layout guidelines.<\/p>\n<p><a class=\"cta-primary\" href=\"https:\/\/tps-elektronik.com\/en\/services\/emv-laboratory\/\">Request an automotive EMC pre-compliance test \u2192<\/a><\/p>\n<\/header><nav class=\"toc\" aria-label=\"Table of contents\">\n<h2 id=\"toc\">Table of Contents<\/h2>\n<ol>\n<li><a href=\"#the-challenge\">The Challenge: CISPR 25 Class 5 Conducted Emissions Failure<\/a><\/li>\n<li><a href=\"#split-ground-plane\">Split Ground Plane: The Hidden Antenna<\/a><\/li>\n<li><a href=\"#common-mode-choke\">Common Mode Choke Placement: Proximity Matters<\/a><\/li>\n<li><a href=\"#pre-compliance-approach\">The Pre-Compliance Advantage: Catching Issues Early<\/a><\/li>\n<li><a href=\"#results\">Results: Passing CISPR 25 Class 5 with Layout Optimizations<\/a><\/li>\n<li><a href=\"#faq\">FAQ<\/a><\/li>\n<\/ol>\n<\/nav>\n<section id=\"the-challenge\">\n<h2>1. The Challenge: CISPR 25 Class 5 Conducted Emissions Failure<\/h2>\n<p>The customer\u2014a German automotive Tier 1 supplier\u2014approached TPS Elektronik with a problem. Their 48 V to 12 V DC-DC converter, designed for an electric vehicle platform. Which had failed conducted emissions testing at an accredited laboratory. The project was behind schedule, and a second failure would trigger a mandatory board redesign. Which costing hundreds of thousands of euros in tooling and validation delays.<\/p>\n<p><strong>CISPR 25 Class 5<\/strong> is the most stringent automotive EMI standard, with limits designed to protect vehicle receivers from disturbances generated by electronic components and modules. Conducted emissions measured from 150 kHz to 108 MHz using a Line Impedance Stabilization Network (LISN) inserted between the power supply and the Device Under Test (DUT). The standard defines five classes, with Class 5 being the most demanding\u2014peak limits in the FM broadcast band (76\u2013108 MHz) are just 38 dB\u03bcV.<\/p>\n<p>The customer&#8217;s design used a 4-layer PCB with a split ground plane intended to isolate the noisy digital\/power domain from the sensitive analog circuitry. A common mode choke placed at the DC input to filter conducted noise. Yet emissions at 80\u201390 MHz consistently exceeded the Class 5 average limit by more than 10 dB\u03bcV.<\/p>\n<p><img decoding=\"async\" class=\"alignnone size-full wp-image-15187\" src=\"https:\/\/tps-elektronik.com\/wp-content\/uploads\/2026\/06\/\u7535\u8def\u677f2.jpg\" alt=\"customized power supply circuit board\" width=\"1920\" height=\"1280\" srcset=\"https:\/\/tps-elektronik.com\/wp-content\/uploads\/2026\/06\/\u7535\u8def\u677f2.jpg 1920w, https:\/\/tps-elektronik.com\/wp-content\/uploads\/2026\/06\/\u7535\u8def\u677f2-600x400.jpg 600w\" sizes=\"(max-width: 1920px) 100vw, 1920px\" \/><\/p>\n<p>TPS&#8217;s <a href=\"https:\/\/tps-elektronik.com\/en\/electromagnetic-compatibility-testing-news\/\">EMC laboratory services<\/a> engaged to perform root-cause analysis and pre-compliance testing. Our team brought the DUT into our Shanghai-based EMC laboratory, which equipped to conduct CISPR 25 pre-compliance measurements using calibrated LISNs, spectrum analyzers, and a CISPR 16-1-1 compliant measuring receiver.<\/p>\n<p><a class=\"cta-primary\" href=\"https:\/\/tps-elektronik.com\/en\/services\/emv-laboratory\/\">Schedule a CISPR 25 pre-compliance test \u2192<\/a><\/p>\n<\/section>\n<section id=\"split-ground-plane\">\n<h2>2. Split Ground Plane: The Hidden Antenna<\/h2>\n<p>Our first diagnostic step was a near-field scan of the PCB. The results were revealing: emissions concentrated around the boundary between the digital\/power ground plane and the analog ground plane. The split in the ground plane\u2014intended to isolate noisy digital currents from sensitive analog circuits. Which had created an impedance discontinuity.<\/p>\n<p>At frequencies above 100 MHz, the slot formed by the split ground plane acts as an effective antenna. High-frequency return currents, unable to flow directly beneath their signal traces. Which forced to find alternative paths around the split boundary. These detours create large loop areas that radiate electromagnetic energy.<\/p>\n<p>In automotive mixed-signal PCBs, a <strong>solid, uninterrupted ground plane<\/strong> with disciplined component placement typically outperforms split ground architectures. However, when isolation between analog and digital domains absolutely required, the split must managed carefully:<\/p>\n<ul>\n<li><strong>Stitching vias<\/strong> must placed at intervals of 10\u201315 mm along the split boundary to provide high-frequency return current paths.<\/li>\n<li><strong>Signal traces must not cross the split<\/strong>\u2014any trace that crosses a ground plane split forces its return current to find a longer path, creating a radiating loop.<\/li>\n<li><strong>High-speed signals<\/strong> (CAN, automotive Ethernet, LVDS) should routed over a continuous ground plane with controlled impedance.<\/li>\n<\/ul>\n<p>Our analysis revealed that the customer&#8217;s PCB had stitching vias spaced at 40\u201350 mm\u2014far too wide for effective high-frequency return current management. Moreover, a critical clock signal trace crossed the split boundary. Which creating a significant radiating loop at its harmonic frequencies.<\/p>\n<p><img decoding=\"async\" class=\"alignnone size-full wp-image-15674\" src=\"https:\/\/tps-elektronik.com\/wp-content\/uploads\/2026\/07\/Split-Ground-Plane-PCB-Layout-with-Stitching-Vias-for-Automotive-EMC-2.jpg\" alt=\"Split ground plane PCB layout showing ground plane stitching and return current path optimization for automotive EMC Split Ground Plane PCB-Layout mit Ground-Plane-Stitching und R\u00fcckstrompfad-Optimierung f\u00fcr Automotive-EMV\" width=\"1920\" height=\"1079\" \/><\/p>\n<p>TPS&#8217;s <a href=\"https:\/\/tps-elektronik.com\/en\/how-to-test-electromagnetic-compatibility-emc-guide\/\">EMC testing guide<\/a> provides additional detail on ground plane design principles. Our <a href=\"https:\/\/tps-elektronik.com\/en\/case-studies\/electromagnetic-compatibility-testing-customer-case\/\">EMC testing customer case studies<\/a> illustrate how we have solved similar issues for other automotive clients.<\/p>\n<\/section>\n<section id=\"common-mode-choke\">\n<h2>3. Common Mode Choke Placement: Proximity Matters<\/h2>\n<p>The second issue identified during our pre-compliance testing was the placement of the common mode choke at the DC input. A common mode choke designed to suppress common mode noise\u2014unwanted currents that flow in the same direction on both the power and return lines. It allows differential signals to pass while presenting high impedance to common mode noise.<\/p>\n<p>However, the effectiveness of a common mode choke depends critically on its placement on the PCB. <strong>The choke must be placed as close to the I\/O connector (the source or exit point of the noise) as physically possible<\/strong>. If placed too far &#8220;inland,&#8221; the PCB traces between the connector and the choke act as antennas, radiating noise before it reaches the filter.<\/p>\n<p>In the customer&#8217;s design, the common mode choke located more than 30 mm from the DC input connector. The intervening traces\u2014approximately 30 mm of copper on the PCB. Which radiating conducted noise at 80\u201390 MHz, explaining the persistent emissions peak.<\/p>\n<p>Additional optimization opportunities identified:<\/p>\n<ul>\n<li><strong>Filter capacitors<\/strong> (both differential-mode and common-mode) should placed on both sides of the choke.<\/li>\n<li><strong>Ferrite beads<\/strong> on power lines can provide additional high-frequency attenuation.<\/li>\n<li><strong>Minimize the loop area<\/strong> of the input power path\u2014the distance between the power trace and its return path should be as small as possible.<\/li>\n<\/ul>\n<p>For automotive DC-DC converters, the conducted EMI noise in the 150 kHz to 30 MHz range primarily comprised of switching frequency harmonics. Above 30 MHz, near-field radiation becomes dominant and EMI filters become less effective due to parasitic capacitance and inductance. Which making layout optimization even more critical.<\/p>\n<p><img decoding=\"async\" class=\"alignnone size-full wp-image-15669\" src=\"https:\/\/tps-elektronik.com\/wp-content\/uploads\/2026\/07\/Common-Mode-Choke-Placement-for-CISPR-25-Conducted-Emissions-3.jpg\" alt=\"Common mode choke placement on automotive PCB near I\/O connector for CISPR 25 conducted emissions optimization Common Mode Choke Platzierung auf automobiler Leiterplatte nahe I\/O-Steckverbinder f\u00fcr CISPR 25 Optimierung\" width=\"1920\" height=\"1079\" \/><\/p>\n<p>TPS&#8217;s <a href=\"https:\/\/tps-elektronik.com\/en\/electromagnetic-compatibility-testing-compliance-guide\/\">EMC compliance guide<\/a> and <a href=\"https:\/\/tps-elektronik.com\/en\/emc-electrical-safety-testing-compliance-reliability\/\">EMC and electrical safety testing resources<\/a> offer comprehensive guidance on filter placement and PCB layout for automotive applications.<\/p>\n<\/section>\n<section id=\"pre-compliance-approach\">\n<h2>4. The Pre-Compliance Advantage: Catching Issues Early<\/h2>\n<p>This case study illustrates why <strong>pre-compliance testing<\/strong> is essential for automotive electronics development. Formal CISPR 25 testing at accredited laboratories is expensive and time-sensitive. A single failure can cost thousands in re-test fees and weeks in schedule delays.<\/p>\n<p>TPS Elektronik&#8217;s EMC laboratory services structured to reduce this risk. Our pre-compliance approach includes:<\/p>\n<ul>\n<li><strong>Early-phase EMC measurements<\/strong> on prototypes before formal testing.<\/li>\n<li><strong>Design-for-EMC guidance<\/strong> during the PCB layout phase.<\/li>\n<li><strong>Root-cause analysis<\/strong> of emissions failures, identifying specific layout issues.<\/li>\n<li><strong>Structured test reports<\/strong> documenting findings and recommended mitigations.<\/li>\n<\/ul>\n<p>Our laboratory equipped to perform CISPR 25 conducted and radiated emissions testing, as well as immunity testing per ISO 11452 and ISO 7637. We support automotive, industrial, medical, and consumer electronics applications.<\/p>\n<p>For this customer, the pre-compliance testing identified the split ground plane and common mode choke placement issues in a single day. The recommended modifications\u2014adding stitching vias, relocating the choke, and rerouting the clock signal. Which implemented in the next PCB revision. The customer returned for a second round of pre-compliance testing, confirming that emissions were now well below Class 5 limits.<\/p>\n<p><a class=\"cta-primary\" href=\"https:\/\/tps-elektronik.com\/en\/services\/emv-laboratory\/\">Request a CISPR 25 pre-compliance test \u2192<\/a><\/p>\n<\/section>\n<section id=\"results\">\n<h2>5. Results: Passing CISPR 25 Class 5 with Layout Optimizations<\/h2>\n<p>The customer implemented the following modifications based on our recommendations:<\/p>\n<ol>\n<li><strong>Ground plane stitching:<\/strong> Added stitching vias at 12 mm intervals along the split boundary, providing high-frequency return current paths.<\/li>\n<li><strong>Common mode choke relocation:<\/strong> Moved the choke to within 5 mm of the DC input connector, minimizing the radiating trace length.<\/li>\n<li><strong>Clock signal rerouting:<\/strong> Rerouted the critical clock signal over a continuous ground plane, eliminating the split crossing.<\/li>\n<li><strong>Additional filter capacitors:<\/strong> Added 100 nF and 1 nF capacitors on both sides of the common mode choke for differential and common mode filtering.<\/li>\n<\/ol>\n<p>After the modifications, the customer returned to TPS&#8217;s EMC laboratory for a second round of pre-compliance testing. The results were conclusive:<\/p>\n<ul>\n<li>Emissions at 80\u201390 MHz reduced by more than 15 dB\u03bcV.<\/li>\n<li>All frequency bands were now at least 6 dB below the CISPR 25 Class 5 average limits.<\/li>\n<li>The design passed formal CISPR 25 conducted emissions testing at the accredited laboratory on the first attempt.<\/li>\n<\/ul>\n<p>The customer avoided a costly board redesign and met their project deadline. The total cost of the TPS pre-compliance testing and consulting services was a fraction of the cost of a single formal certification failure.<\/p>\n<p>For more automotive EMC case studies, see our <a href=\"https:\/\/tps-elektronik.com\/en\/case-studies\/electromagnetic-compatibility-electrical-safety-testing-case\/\">combined EMC and electrical safety testing case<\/a> and <a href=\"https:\/\/tps-elektronik.com\/en\/case-studies\/emc-testing-collaboration-tps-elektronik\/\">EMC testing collaboration case<\/a>.<\/p>\n<p><a class=\"cta-primary\" href=\"https:\/\/tps-elektronik.com\/en\/services\/emv-laboratory\/\">Contact TPS for automotive EMC testing \u2192<\/a><\/p>\n<\/section>\n<section id=\"faq\">\n<h2>6. FAQ<\/h2>\n<div>\n<div>\n<h3>What is CISPR 25 Class 5 and why is it the most stringent automotive EMC standard?<\/h3>\n<div>\n<div>CISPR 25 Class 5 defines the most demanding conducted and radiated emission limits for automotive components. Class 5 limits are significantly lower than Classes 1\u20134, particularly in the FM broadcast band (76\u2013108 MHz) where the peak limit is just 38 dB\u03bcV. Most automotive OEMs require Class 5 compliance for electronic modules.<\/div>\n<\/div>\n<\/div>\n<div>\n<h3>Why does a split ground plane cause conducted emissions failures in automotive PCBs?<\/h3>\n<div>\n<div>A split ground plane creates an impedance discontinuity\u2014a &#8220;slot&#8221; that acts as an antenna at frequencies where the slot length approaches a quarter wavelength. High-frequency return currents forced to find alternative paths around the split, creating large radiating loops. A solid, uninterrupted ground plane typically outperforms split architectures in automotive mixed-signal designs.<\/div>\n<\/div>\n<\/div>\n<div>\n<h3>Where should a common mode choke be placed on a PCB for optimal EMI suppression?<\/h3>\n<div>\n<div>A common mode choke should placed as close to the I\/O connector (the source or exit point of noise) as physically possible. Traces between the connector and the choke act as antennas, radiating noise before it reaches the filter. Filter capacitors should placed on both sides of the choke.<\/div>\n<\/div>\n<\/div>\n<div>\n<h3>What is the difference between pre-compliance and formal CISPR 25 testing?<\/h3>\n<div>\n<div>Pre-compliance testing performed during development to identify and fix EMC issues before formal certification. It uses the same methods and standards as accredited labs (CISPR 25, CISPR 16-1-1) but allows iterative design changes. Formal testing is the final verification performed by an accredited laboratory for regulatory compliance.<\/div>\n<\/div>\n<\/div>\n<div>\n<h3>Can TPS perform full CISPR 25 conducted emissions testing?<\/h3>\n<div>\n<div>TPS performs CISPR 25 pre-compliance testing in our fully equipped EMC laboratory in Shanghai. We measure conducted emissions from 150 kHz to 108 MHz using calibrated LISNs and CISPR 16-1-1 compliant receivers. We provide structured test reports and engineering recommendations for optimization.<\/div>\n<\/div>\n<\/div>\n<div>\n<h3>What other automotive EMC standards does TPS support?<\/h3>\n<div>\n<div>In addition to CISPR 25, TPS supports ISO 11452 (component-level immunity testing), ISO 7637 (electrical transient testing), and OEM-specific requirements. Our laboratory is IATF 16949 certified for automotive electronics.<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n<footer style=\"background: #2d5797; padding: 30px; border-radius: 14px; margin-top: 40px;\">\n<p style=\"color: #ffffff; font-size: 16px; line-height: 1.6; margin: 0;\"><strong>Ready to pass CISPR 25 Class 5 conducted emissions on your next automotive project?<\/strong><br \/>Contact TPS Elektronik for pre-compliance testing, design reviews, and EMC layout guidance\u2014from prototype evaluation through formal certification support.<br \/><a style=\"color: #ffffff; font-weight: 600; text-decoration: underline;\" href=\"https:\/\/tps-elektronik.com\/en\/services\/emv-laboratory\/\">Request your automotive EMC consultation \u2192<\/a><\/p>\n<\/footer><\/article>\n\n<style id=\"wpforms-css-vars-4659-block-80739bde-ced3-4df8-8a86-632e30b53ad4\">\n\t\t\t\t#wpforms-4659.wpforms-block-80739bde-ced3-4df8-8a86-632e30b53ad4 {\n\t\t\t\t--wpforms-field-size-input-height: 43px;\n--wpforms-field-size-input-spacing: 15px;\n--wpforms-field-size-font-size: 16px;\n--wpforms-field-size-line-height: 19px;\n--wpforms-field-size-padding-h: 14px;\n--wpforms-field-size-checkbox-size: 16px;\n--wpforms-field-size-sublabel-spacing: 5px;\n--wpforms-field-size-icon-size: 1;\n--wpforms-label-size-font-size: 16px;\n--wpforms-label-size-line-height: 19px;\n--wpforms-label-size-sublabel-font-size: 14px;\n--wpforms-label-size-sublabel-line-height: 17px;\n--wpforms-button-size-font-size: 17px;\n--wpforms-button-size-height: 41px;\n--wpforms-button-size-padding-h: 15px;\n--wpforms-button-size-margin-top: 10px;\n\t\t\t}\n\t\t\t<\/style><div class=\"wpforms-container wpforms-container-full wpforms-block wpforms-block-80739bde-ced3-4df8-8a86-632e30b53ad4 wpforms-render-modern\" id=\"wpforms-4659\"><form id=\"wpforms-form-4659\" class=\"wpforms-validate wpforms-form wpforms-ajax-form\" data-formid=\"4659\" method=\"post\" enctype=\"multipart\/form-data\" action=\"\/en\/wp-json\/wp\/v2\/case_studies\/15553\" data-token=\"9a68e52afdc2b0886bba9b833c568437\" data-token-time=\"1786446005\"><noscript class=\"wpforms-error-noscript\">Please enable JavaScript in your browser to complete this form.<\/noscript><div id=\"wpforms-error-noscript\" style=\"display: none;\">Please enable JavaScript in your browser to complete this form.<\/div><div class=\"wpforms-field-container\"><div id=\"wpforms-4659-field_1-container\" class=\"wpforms-field wpforms-field-name\" data-field-id=\"1\"><fieldset><legend class=\"wpforms-field-label\">Name <span class=\"wpforms-required-label\" aria-hidden=\"true\">*<\/span><\/legend><div class=\"wpforms-field-row wpforms-field-large\"><div class=\"wpforms-field-row-block wpforms-first wpforms-one-half\"><input type=\"text\" id=\"wpforms-4659-field_1\" class=\"wpforms-field-name-first wpforms-field-required\" name=\"wpforms[fields][1][first]\" aria-errormessage=\"wpforms-4659-field_1-error\" required><label for=\"wpforms-4659-field_1\" class=\"wpforms-field-sublabel after\">First<\/label><\/div><div class=\"wpforms-field-row-block wpforms-one-half\"><input type=\"text\" id=\"wpforms-4659-field_1-last\" class=\"wpforms-field-name-last wpforms-field-required\" name=\"wpforms[fields][1][last]\" aria-errormessage=\"wpforms-4659-field_1-last-error\" required><label for=\"wpforms-4659-field_1-last\" class=\"wpforms-field-sublabel after\">Last<\/label><\/div><\/div><\/fieldset><\/div><div id=\"wpforms-4659-field_4-container\" class=\"wpforms-field wpforms-field-text\" data-field-id=\"4\"><label class=\"wpforms-field-label\" for=\"wpforms-4659-field_4\">Company <span class=\"wpforms-required-label\" aria-hidden=\"true\">*<\/span><\/label><input type=\"text\" id=\"wpforms-4659-field_4\" class=\"wpforms-field-large wpforms-field-required\" name=\"wpforms[fields][4]\" aria-errormessage=\"wpforms-4659-field_4-error\" required><\/div><div id=\"wpforms-4659-field_2-container\" class=\"wpforms-field wpforms-field-email\" data-field-id=\"2\"><label class=\"wpforms-field-label\" for=\"wpforms-4659-field_2\">Email <span class=\"wpforms-required-label\" aria-hidden=\"true\">*<\/span><\/label><input type=\"email\" id=\"wpforms-4659-field_2\" class=\"wpforms-field-large wpforms-field-required\" name=\"wpforms[fields][2]\" spellcheck=\"false\" aria-errormessage=\"wpforms-4659-field_2-error\" required><\/div>\t\t<div id=\"wpforms-4659-field_5-container\"\n\t\t\tclass=\"wpforms-field wpforms-field-text\"\n\t\t\tdata-field-type=\"text\"\n\t\t\tdata-field-id=\"5\"\n\t\t\t>\n\t\t\t<label class=\"wpforms-field-label\" for=\"wpforms-4659-field_5\" >Email Comment or<\/label>\n\t\t\t<input type=\"text\" id=\"wpforms-4659-field_5\" class=\"wpforms-field-medium\" name=\"wpforms[fields][5]\" >\n\t\t<\/div>\n\t\t<div id=\"wpforms-4659-field_3-container\" class=\"wpforms-field wpforms-field-textarea\" data-field-id=\"3\"><label class=\"wpforms-field-label\" for=\"wpforms-4659-field_3\">Comment or Message<\/label><textarea id=\"wpforms-4659-field_3\" class=\"wpforms-field-medium\" name=\"wpforms[fields][3]\" aria-errormessage=\"wpforms-4659-field_3-error\" ><\/textarea><\/div><div id=\"wpforms-4659-field_6-container\" class=\"wpforms-field wpforms-field-checkbox\" data-field-id=\"6\"><fieldset><legend class=\"wpforms-field-label wpforms-label-hide\" aria-hidden=\"false\">Checkbox <span class=\"wpforms-required-label\" aria-hidden=\"true\">*<\/span><\/legend><ul id=\"wpforms-4659-field_6\" class=\"wpforms-field-required\"><li class=\"choice-1 depth-1 wpforms-selected\"><input type=\"checkbox\" id=\"wpforms-4659-field_6_1\" name=\"wpforms[fields][6][]\" value=\"I agree to the processing of my information for the purpose of creating a quote.\" aria-errormessage=\"wpforms-4659-field_6_1-error\" aria-describedby=\"wpforms-4659-field_6-description\" required  checked='checked'><label class=\"wpforms-field-label-inline\" for=\"wpforms-4659-field_6_1\">I agree to the processing of my information for the purpose of creating a quote.<\/label><\/li><\/ul><div id=\"wpforms-4659-field_6-description\" class=\"wpforms-field-description\">For information see Privacy.<\/div><\/fieldset><\/div><script>\n\t\t\t\t( function() {\n\t\t\t\t\tconst style = document.createElement( 'style' );\n\t\t\t\t\tstyle.appendChild( document.createTextNode( '#wpforms-4659-field_5-container { position: absolute !important; overflow: hidden !important; display: inline !important; height: 1px !important; width: 1px !important; z-index: -1000 !important; padding: 0 !important; } #wpforms-4659-field_5-container input { visibility: hidden; } #wpforms-conversational-form-page #wpforms-4659-field_5-container label { counter-increment: none; }' ) );\n\t\t\t\t\tdocument.head.appendChild( style );\n\t\t\t\t\tdocument.currentScript?.remove();\n\t\t\t\t} )();\n\t\t\t<\/script><\/div><!-- .wpforms-field-container --><div class=\"wpforms-submit-container\" ><input type=\"hidden\" name=\"wpforms[id]\" value=\"4659\"><input type=\"hidden\" name=\"page_title\" value=\"\"><input type=\"hidden\" name=\"page_url\" value=\"https:\/\/tps-elektronik.com\/en\/wp-json\/wp\/v2\/case_studies\/15553\"><input type=\"hidden\" name=\"url_referer\" value=\"\"><button type=\"submit\" name=\"wpforms[submit]\" id=\"wpforms-submit-4659\" class=\"wpforms-submit\" data-alt-text=\"Sending...\" data-submit-text=\"Submit\" aria-live=\"assertive\" value=\"wpforms-submit\">Submit<\/button><img decoding=\"async\" src=\"https:\/\/tps-elektronik.com\/wp-content\/plugins\/wpforms-lite\/assets\/images\/submit-spin.svg\" class=\"wpforms-submit-spinner\" style=\"display: none;\" width=\"26\" height=\"26\" alt=\"Loading\"><\/div><\/form><\/div>  <!-- .wpforms-container -->\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n","protected":false},"excerpt":{"rendered":"<p>A German automotive Tier 1 supplier faced a critical project milestone: their 48 V to 12 V DC-DC converter for an electric vehicle platform had to pass CISPR 25 Class 5 conducted emissions. The most stringent automotive EMI standard. Initial pre-compliance testing at TPS Elektronik&#8217;s EMC laboratory revealed excessive noise across the AM and FM\u2026 <a href=\"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/\">Read More &raquo;<\/a><\/p>\n","protected":false},"author":9,"featured_media":15187,"template":"","class_list":["post-15553","case_studies","type-case_studies","status-publish","has-post-thumbnail","hentry"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.2 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>TPS EMC Layout Guidelines - TPS<\/title>\n<meta name=\"description\" content=\"CISPR 25 Class 5 conducted emissions passed with split ground plane and common mode choke placement. EMC layout guidelines for automotive DC-DC converters.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"TPS EMC Layout Guidelines - TPS\" \/>\n<meta property=\"og:description\" content=\"CISPR 25 Class 5 conducted emissions passed with split ground plane and common mode choke placement. EMC layout guidelines for automotive DC-DC converters.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/\" \/>\n<meta property=\"og:site_name\" content=\"TPS\" \/>\n<meta property=\"og:image\" content=\"https:\/\/tps-elektronik.com\/wp-content\/uploads\/2026\/06\/\u7535\u8def\u677f2.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"1920\" \/>\n\t<meta property=\"og:image:height\" content=\"1280\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"9 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/case-studies\\\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\\\/\",\"url\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/case-studies\\\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\\\/\",\"name\":\"TPS EMC Layout Guidelines - TPS\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/case-studies\\\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\\\/#primaryimage\"},\"image\":{\"@id\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/case-studies\\\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/tps-elektronik.com\\\/wp-content\\\/uploads\\\/2026\\\/06\\\/\u7535\u8def\u677f2.jpg\",\"datePublished\":\"2026-08-11T07:00:00+00:00\",\"description\":\"CISPR 25 Class 5 conducted emissions passed with split ground plane and common mode choke placement. EMC layout guidelines for automotive DC-DC converters.\",\"breadcrumb\":{\"@id\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/case-studies\\\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\\\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/case-studies\\\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\\\/\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/case-studies\\\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\\\/#primaryimage\",\"url\":\"https:\\\/\\\/tps-elektronik.com\\\/wp-content\\\/uploads\\\/2026\\\/06\\\/\u7535\u8def\u677f2.jpg\",\"contentUrl\":\"https:\\\/\\\/tps-elektronik.com\\\/wp-content\\\/uploads\\\/2026\\\/06\\\/\u7535\u8def\u677f2.jpg\",\"width\":1920,\"height\":1280,\"caption\":\"customized power supply circuit board\"},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/case-studies\\\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\\\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Startseite\",\"item\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Case Studies\",\"item\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/case-studies\\\/\"},{\"@type\":\"ListItem\",\"position\":3,\"name\":\"How to Pass Automotive Conducted Emissions CISPR 25 Class 5 with TPS Split Ground Plane and Common Mode Choke Placement \u2013 EMC Layout Guidelines for Automotive DC-DC Converters?\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/#website\",\"url\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/\",\"name\":\"TPS\",\"description\":\"\",\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\\\/\\\/tps-elektronik.com\\\/en\\\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"TPS EMC Layout Guidelines - TPS","description":"CISPR 25 Class 5 conducted emissions passed with split ground plane and common mode choke placement. EMC layout guidelines for automotive DC-DC converters.","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/","og_locale":"en_US","og_type":"article","og_title":"TPS EMC Layout Guidelines - TPS","og_description":"CISPR 25 Class 5 conducted emissions passed with split ground plane and common mode choke placement. EMC layout guidelines for automotive DC-DC converters.","og_url":"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/","og_site_name":"TPS","og_image":[{"width":1920,"height":1280,"url":"https:\/\/tps-elektronik.com\/wp-content\/uploads\/2026\/06\/\u7535\u8def\u677f2.jpg","type":"image\/jpeg"}],"twitter_card":"summary_large_image","twitter_misc":{"Est. reading time":"9 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"WebPage","@id":"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/","url":"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/","name":"TPS EMC Layout Guidelines - TPS","isPartOf":{"@id":"https:\/\/tps-elektronik.com\/en\/#website"},"primaryImageOfPage":{"@id":"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/#primaryimage"},"image":{"@id":"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/#primaryimage"},"thumbnailUrl":"https:\/\/tps-elektronik.com\/wp-content\/uploads\/2026\/06\/\u7535\u8def\u677f2.jpg","datePublished":"2026-08-11T07:00:00+00:00","description":"CISPR 25 Class 5 conducted emissions passed with split ground plane and common mode choke placement. EMC layout guidelines for automotive DC-DC converters.","breadcrumb":{"@id":"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/#breadcrumb"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/"]}]},{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/#primaryimage","url":"https:\/\/tps-elektronik.com\/wp-content\/uploads\/2026\/06\/\u7535\u8def\u677f2.jpg","contentUrl":"https:\/\/tps-elektronik.com\/wp-content\/uploads\/2026\/06\/\u7535\u8def\u677f2.jpg","width":1920,"height":1280,"caption":"customized power supply circuit board"},{"@type":"BreadcrumbList","@id":"https:\/\/tps-elektronik.com\/en\/case-studies\/how-to-pass-automotive-conducted-emissions-cispr-25-class-5-with-tps-split-ground-plane-and-common-mode-choke-placement-emc-layout-guidelines-for-automotive-dc-dc-converters\/#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Startseite","item":"https:\/\/tps-elektronik.com\/en\/"},{"@type":"ListItem","position":2,"name":"Case Studies","item":"https:\/\/tps-elektronik.com\/en\/case-studies\/"},{"@type":"ListItem","position":3,"name":"How to Pass Automotive Conducted Emissions CISPR 25 Class 5 with TPS Split Ground Plane and Common Mode Choke Placement \u2013 EMC Layout Guidelines for Automotive DC-DC Converters?"}]},{"@type":"WebSite","@id":"https:\/\/tps-elektronik.com\/en\/#website","url":"https:\/\/tps-elektronik.com\/en\/","name":"TPS","description":"","potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/tps-elektronik.com\/en\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"}]}},"_links":{"self":[{"href":"https:\/\/tps-elektronik.com\/en\/wp-json\/wp\/v2\/case_studies\/15553","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/tps-elektronik.com\/en\/wp-json\/wp\/v2\/case_studies"}],"about":[{"href":"https:\/\/tps-elektronik.com\/en\/wp-json\/wp\/v2\/types\/case_studies"}],"author":[{"embeddable":true,"href":"https:\/\/tps-elektronik.com\/en\/wp-json\/wp\/v2\/users\/9"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/tps-elektronik.com\/en\/wp-json\/wp\/v2\/media\/15187"}],"wp:attachment":[{"href":"https:\/\/tps-elektronik.com\/en\/wp-json\/wp\/v2\/media?parent=15553"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}