1 A Low-Dropout Regulator AMS - AMS1117 - readme.html

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<div class=ident><h1>AMS1117</h1><span class=mfr>Advanced Monolithic Systems</span><span class=badge>1 A LDO &middot; AMS</span></div>
<p class=oneline>The <b>original</b> AMS1117: a three-terminal <b>1 A low-dropout linear voltage regulator</b> from Advanced Monolithic Systems, in fixed 1.5 / 1.8 / 2.5 / 2.85 / 3.3 / 5.0 V versions or an adjustable version set by two resistors around a 1.25 V reference. Operates down to <b>1 V input-to-output differential</b> (1.3 V max dropout at 0.8 A), trimmed on-chip to 1.5 %, with internal current limit and thermal shutdown. Pin-compatible with older three-terminal SCSI regulators. Offered in SOT-223, TO-252 (DPAK) and 8-lead SOIC.</p>
<div class=sib><b>This page is the Advanced Monolithic Systems part only.</b> Everything below comes from the AMS datasheet and applies to AMS-branded silicon. The same part number is second-sourced by UMW with a <b>different voltage lineup, different packages and materially different limits</b>. If your BOM says UMW, use <a href="https://wiki.adom.inc/adom/umw-ams1117">1 A Low-Dropout Regulator UMW - AMS1117</a> instead.</div>
<div class=metarow>
<span class=m>Output <b>1 A</b></span><span class=m>Dropout <b>1.3 V max</b></span><span class=m>V<sub>IN</sub> <b>15 V max</b></span>
<span class=m>Versions <b>6 fixed + ADJ</b></span><span class=m>Packages <b>SOT-223 · TO-252 · SO-8</b></span><span class=m>Pins <b>3 (8 on SO-8)</b></span>
</div>

<h2>At a glance</h2>
<div class=grid>
<div class=card><div class="k" style="color:#00b8b1">Output current</div><div class=v>1 A</div><div class=s>Current limit 1.1 A typ &middot; 900 mA min</div></div>
<div class=card><div class="k" style="color:#28c3d4">Dropout</div><div class=v>1.3 V max</div><div class=s>1.1 V typ at I<sub>OUT</sub> = 0.8 A</div></div>
<div class=card><div class="k" style="color:#4fb7f0">Fixed outputs</div><div class=v>6 versions</div><div class=s>1.5 &middot; 1.8 &middot; 2.5 &middot; 2.85 &middot; 3.3 &middot; 5.0 V</div></div>
<div class=card><div class="k" style="color:#64abff">Adjustable</div><div class=v>1.25 V ref</div><div class=s>V<sub>OUT</sub> = V<sub>REF</sub>(1 + R2/R1) + I<sub>ADJ</sub>R2</div></div>
<div class=card><div class="k" style="color:#8c6bf7">Packages</div><div class=v>3 options</div><div class=s>SOT-223 &middot; TO-252 (DPAK) &middot; 8L SOIC</div></div>
<div class=card><div class="k" style="color:#a98bf9">Junction temp</div><div class=v>&minus;40 to +125 &deg;C</div><div class=s>Thermal shutdown at 165 &deg;C</div></div>
</div>

<h2>Specifications</h2>
<div>
<div class=spec><span class=lbl>Output current</span><span>1 A</span></div>
<div class=spec><span class=lbl>Fixed output voltages</span><span>1.5 / 1.8 / 2.5 / 2.85 / 3.3 / 5.0 V. Also available adjustable</span></div>
<div class=spec><span class=lbl>Reference voltage</span><span>1.250 V typ (1.232 to 1.268 V at 25 &deg;C, I<sub>OUT</sub> = 10 mA)</span></div>
<div class=spec><span class=lbl>Dropout voltage</span><span>1.1 V typ, 1.3 V max at I<sub>OUT</sub> = 0.8 A. Higher above 0.8 A</span></div>
<div class=spec><span class=lbl>Input voltage</span><span>15 V absolute maximum</span></div>
<div class=spec><span class=lbl>Line regulation</span><span>0.2 % max (0.015 % typ)</span></div>
<div class=spec><span class=lbl>Load regulation</span><span>0.4 % max (0.1 % typ), 10 mA &le; I<sub>OUT</sub> &le; 0.8 A</span></div>
<div class=spec><span class=lbl>Current limit</span><span>900 mA min / 1100 mA typ / 1500 mA max at V<sub>IN</sub> &minus; V<sub>OUT</sub> = 1.5 V</span></div>
<div class=spec><span class=lbl>Quiescent current</span><span>5 mA typ, 11 mA max</span></div>
<div class=spec><span class=lbl>Minimum load current</span><span>5 mA typ, 10 mA max (adjustable version)</span></div>
<div class=spec><span class=lbl>Ripple rejection</span><span>60 dB min; 75 dB typ adjustable, 72 dB fixed, 68 dB on the 5.0 V version (120 Hz, C<sub>OUT</sub> = 22 &micro;F)</span></div>
<div class=spec><span class=lbl>Adjust pin current</span><span>55 &micro;A typ, 120 &micro;A max &middot; change 0.2 &micro;A typ, 5 &micro;A max</span></div>
<div class=spec><span class=lbl>Thermal regulation</span><span>0.008 %/W typ, 0.04 %/W max (30 ms pulse)</span></div>
<div class=spec><span class=lbl>RMS output noise</span><span>0.003 % of V<sub>OUT</sub> (10 Hz to 10 kHz)</span></div>
<div class=spec><span class=lbl>Temperature stability</span><span>0.5 % typ</span></div>
<div class=spec><span class=lbl>Long term stability</span><span>0.3 % typ, 1 % max (1000 h at 125 &deg;C)</span></div>
<div class=spec><span class=lbl>Protection</span><span>Internal current limit + thermal shutdown at 165 &deg;C junction</span></div>
<div class=spec><span class=lbl>Thermal resistance &theta;<sub>JA</sub></span><span>SOT-223 90 &deg;C/W* &middot; TO-252 80 &deg;C/W &middot; SO-8 160 &deg;C/W &nbsp;(*46 &deg;C/W achievable with copper area)</span></div>
<div class=spec><span class=lbl>Thermal resistance &theta;<sub>JC</sub></span><span>15 &deg;C/W max, all packages</span></div>
<div class=spec><span class=lbl>Operating junction temp</span><span>&minus;40 to +125 &deg;C &middot; storage &minus;65 to +150 &deg;C</span></div>
<div class=spec><span class=lbl>Soldering</span><span>Lead temperature 265 &deg;C, 25 s</span></div>
<div class=spec><span class=lbl>Required output cap</span><span>22 &micro;F solid tantalum. Part of the loop compensation, not optional</span></div>
</div>

<h2>Symbol &amp; footprint</h2>
<div class=viewers2>
<div><div class=vh>Schematic symbol: hover a pin for its function</div>
<iframe class=vframe height=520 loading=lazy title="AMS1117 schematic symbol" src="https://wiki.adom.inc/api/v1/pages/adom/ams-ams1117/files/viewer-symbol.html"></iframe></div>
<div><div class=vh>PCB footprint: switch package bottom-right (SOT-223 / TO-252 / SO-8)</div>
<iframe class=vframe height=520 loading=lazy title="AMS1117 footprint (SOT-223 / TO-252 / SO-8)" src="https://wiki.adom.inc/api/v1/pages/adom/ams-ams1117/files/viewer-footprints.html"></iframe></div>
</div>

<h2>Pin map <span style="color:var(--text-2);font-weight:400;font-size:14px">3 terminals on SOT-223 / TO-252, 8 leads on SOIC</span></h2>
<div class=callout>On <b>both SOT-223 and TO-252 the metal tab is V<sub>OUT</sub></b>, internally bonded to pin 2. It is the heat path, so it must be soldered to a copper pour on the output net, never to ground. Both footprints shipped here carry the tab as pad 2.</div>
<div class=pinwrap>
<div class=pg><div class=pgh style="border-color:#00b8b1"><span class=dot style="background:#00b8b1"></span>SOT-223 &amp; TO-252<span class=ct>3 + tab</span></div><table class=pt><tbody>
<tr><td class=pn>1</td><td class=nm>GND/ADJ</td><td class=fx>Ground on fixed versions; feedback (adjust) node on the adjustable version</td></tr>
<tr><td class=pn>2</td><td class=nm>VOUT</td><td class=fx>Regulated output. Also the metal tab</td></tr>
<tr><td class=pn>3</td><td class=nm>VIN</td><td class=fx>Unregulated input, 15 V max</td></tr>
<tr><td class=pn>n/a</td><td class=nm>TAB</td><td class=fx>Thermal pad, bonded to pin 2 (V<sub>OUT</sub>)</td></tr>
</tbody></table></div>
<div class=pg><div class=pgh style="border-color:#8c6bf7"><span class=dot style="background:#8c6bf7"></span>8-lead SOIC<span class=ct>8</span></div><table class=pt><tbody>
<tr><td class=pn>1</td><td class=nm>GND/ADJ</td><td class=fx>Ground on fixed versions; adjust node on the adjustable version</td></tr>
<tr><td class=pn>2</td><td class=nm>VOUT</td><td class=fx>Regulated output</td></tr>
<tr><td class=pn>3</td><td class=nm>VOUT</td><td class=fx>Regulated output. Tie all V<sub>OUT</sub> leads together</td></tr>
<tr><td class=pn>4</td><td class=nm>VIN</td><td class=fx>Unregulated input, 15 V max</td></tr>
<tr><td class=pn>5</td><td class=nm>N/C</td><td class=fx>No internal connection</td></tr>
<tr><td class=pn>6</td><td class=nm>VOUT</td><td class=fx>Regulated output</td></tr>
<tr><td class=pn>7</td><td class=nm>VOUT</td><td class=fx>Regulated output</td></tr>
<tr><td class=pn>8</td><td class=nm>N/C</td><td class=fx>No internal connection</td></tr>
</tbody></table></div>
</div>

<h2>Component variants</h2>
<div class=callout>All variants are the <b>same AMS1117 silicon</b>. The order code carries two independent choices: the <b>package</b> (a letter pair after the base part) and the <b>output voltage</b> (a suffix). A blank voltage suffix means the <b>adjustable</b> version. Every version is available in all three packages.</div>
<div class=occode>
<div class=ocbig><span style="color:#e6edf3">AMS1117</span><span style="color:#8c6bf7">CD</span><span style="color:#00e6dc">-3.3</span></div>
<div class=oclegend>
<div class=ocitem><div class=octop><span class=sw style="background:#8b949e"></span><b style="color:#e6edf3">AMS1117</b></div><div class=ocdesc>base part: 1 A LDO</div></div>
<div class=ocitem><div class=octop><span class=sw style="background:#8c6bf7"></span><b style="color:#a98bf9">CD / CS / blank</b></div><div class=ocdesc><code>CD</code> = TO-252 (DPAK) &middot; <code>CS</code> = 8-lead SOIC &middot; blank = SOT-223</div></div>
<div class=ocitem><div class=octop><span class=sw style="background:#00e6dc"></span><b style="color:#00e6dc">-3.3</b></div><div class=ocdesc>fixed output voltage. Blank means the adjustable version</div></div>
</div>
</div>
<div class=vgrid>
<div class=vcard>
<h3>SOT-223<span class=chip style="background:rgba(139,148,158,.18);color:#8b949e">no letter</span></h3>
<div class=sub>6.30 to 6.71 &times; 3.30 to 3.71 mm, 1.80 mm max height &middot; 2.30 mm lead pitch &middot; tab = V<sub>OUT</sub></div>
<div class=oc><b>Fixed:</b> <code>AMS1117-1.5</code> <code>-1.8</code> <code>-2.5</code> <code>-2.85</code> <code>-3.3</code> <code>-5.0</code></div>
<div class=oc><b>Adjustable:</b> <code>AMS1117</code></div>
<div class=oc>&theta;<sub>JA</sub> <b>90 &deg;C/W</b> &middot; 1.2 W max dissipation</div>
</div>
<div class=vcard>
<h3>TO-252 (DPAK) <code style="font-size:13px">CD</code></h3>
<div class=sub>6.48 to 6.73 &times; 5.97 to 6.22 mm body, 2.21 to 2.39 mm height &middot; tab = V<sub>OUT</sub></div>
<div class=oc><b>Fixed:</b> <code>AMS1117CD-1.5</code> <code>-1.8</code> <code>-2.5</code> <code>-2.85</code> <code>-3.3</code> <code>-5.0</code></div>
<div class=oc><b>Adjustable:</b> <code>AMS1117CD</code></div>
<div class=oc>&theta;<sub>JA</sub> <b>80 &deg;C/W</b> &middot; 2.2 W max dissipation. The best thermal option</div>
</div>
<div class=vcard>
<h3>8-lead SOIC <code style="font-size:13px">CS</code></h3>
<div class=sub>4.80 to 5.00 &times; 3.81 to 3.99 mm body, 1.27 mm pitch &middot; V<sub>OUT</sub> on four leads</div>
<div class=oc><b>Fixed:</b> <code>AMS1117CS-1.5</code> <code>-1.8</code> <code>-2.5</code> <code>-2.85</code> <code>-3.3</code> <code>-5.0</code></div>
<div class=oc><b>Adjustable:</b> <code>AMS1117CS</code></div>
<div class=oc>&theta;<sub>JA</sub> <b>160 &deg;C/W</b> &middot; 780 mW max dissipation: lowest power</div>
</div>
</div>

<h2>Output voltage versions</h2>
<p style="color:var(--text-2);font-size:14px;margin:0 0 10px">Limits at T<sub>J</sub> = 25 &deg;C. The test V<sub>IN</sub> is the datasheet condition for each part; load regulation is measured at 0 &le; I<sub>OUT</sub> &le; 0.8 A.</p>
<table class=vt><thead><tr><th>Version</th><th>V<sub>OUT</sub> typ</th><th>Min to max</th><th>Test V<sub>IN</sub></th><th>Line reg. typ / max</th><th>Load reg. typ / max</th><th>Ripple rej. typ</th></tr></thead><tbody>
<tr><td>AMS1117-1.5</td><td>1.500 V</td><td>1.478 to 1.522 V</td><td>3.0 V</td><td>0.3 / 5 mV</td><td>3 / 10 mV</td><td>72 dB</td></tr>
<tr><td>AMS1117-1.8</td><td>1.800 V</td><td>1.773 to 1.827 V</td><td>3.3 V</td><td>0.3 / 5 mV</td><td>3 / 10 mV</td><td>72 dB</td></tr>
<tr><td>AMS1117-2.5</td><td>2.500 V</td><td>2.463 to 2.537 V</td><td>4.0 V</td><td>0.3 / 6 mV</td><td>3 / 12 mV</td><td>72 dB</td></tr>
<tr><td>AMS1117-2.85</td><td>2.850 V</td><td>2.808 to 2.892 V</td><td>4.35 V</td><td>0.3 / 6 mV</td><td>3 / 12 mV</td><td>72 dB</td></tr>
<tr><td>AMS1117-3.3</td><td>3.300 V</td><td>3.251 to 3.349 V</td><td>4.8 V</td><td>0.5 / 10 mV</td><td>3 / 15 mV</td><td>72 dB</td></tr>
<tr><td>AMS1117-5.0</td><td>5.000 V</td><td>4.925 to 5.075 V</td><td>6.5 V</td><td>0.5 / 10 mV</td><td>5 / 20 mV</td><td>68 dB</td></tr>
<tr><td>AMS1117 (ADJ)</td><td>1.250 V ref</td><td>1.232 to 1.268 V</td><td>n/a</td><td>0.015 / 0.2 %</td><td>0.1 / 0.3 %</td><td>75 dB</td></tr>
</tbody></table>
<p style="color:var(--text-3);font-size:13px;margin:10px 0 0"><b>2.85 V is here for SCSI.</b> It is the SCSI-2 active-termination voltage. The datasheet lists "Active SCSI Terminators" as an application, and 2.85 V regulators exist almost entirely to hold a SCSI bus at spec through 110 &Omega; series resistors. It is the one version the UMW second source does not carry.</p>

<h2>Thermal design</h2>
<p style="color:var(--text-2);font-size:14px;margin:0 0 10px">P<sub>D</sub> = (V<sub>IN</sub> &minus; V<sub>OUT</sub>) &times; I<sub>OUT</sub>, and T<sub>J</sub> = T<sub>A(max)</sub> + P<sub>D</sub>&theta;<sub>JA</sub> must stay under 125 &deg;C. The datasheet's measured SOT-223 &theta;<sub>JA</sub> against copper area, on 1/16" FR-4 with 1 oz foil:</p>
<table class=vt><thead><tr><th>Top-side copper</th><th>Back-side copper</th><th>Board area</th><th>&theta;<sub>JA</sub></th></tr></thead><tbody>
<tr><td>2500 mm&sup2;</td><td>2500 mm&sup2;</td><td>2500 mm&sup2;</td><td>55 &deg;C/W</td></tr>
<tr><td>1000 mm&sup2;</td><td>2500 mm&sup2;</td><td>2500 mm&sup2;</td><td>55 &deg;C/W</td></tr>
<tr><td>225 mm&sup2;</td><td>2500 mm&sup2;</td><td>2500 mm&sup2;</td><td>65 &deg;C/W</td></tr>
<tr><td>100 mm&sup2;</td><td>2500 mm&sup2;</td><td>2500 mm&sup2;</td><td>80 &deg;C/W</td></tr>
<tr><td>1000 mm&sup2;</td><td>1000 mm&sup2;</td><td>1000 mm&sup2;</td><td>60 &deg;C/W</td></tr>
<tr><td>1000 mm&sup2;</td><td>0</td><td>1000 mm&sup2;</td><td>65 &deg;C/W</td></tr>
</tbody></table>
<p style="color:var(--text-3);font-size:13px;margin:10px 0 0">The tab is attached to the top-side copper in every row. Note the spreading copper does <b>not</b> have to be electrically connected to the tab to be effective. A plane on the opposite side of the board works.</p>

<h2>Assets</h2>
<p style="color:var(--text-2);font-size:14px;margin:0 0 10px">KiCad symbol, all three footprints and matching 3D models, plus the canonical <b>adom-lbr JSON</b> the rest is generated from.</p>
<table class=at><tbody>
<tr><td class=tool style="color:#00b8b1">KiCad symbols</td><td><a href=ams1117.kicad_sym>ams1117.kicad_sym</a> (3-pin) &middot; <a href=ams1117-so8.kicad_sym>ams1117-so8.kicad_sym</a> (8-lead)</td></tr>
<tr><td class=tool style="color:#28c3d4">KiCad footprints</td><td><a href=ams1117-sot223.kicad_mod>AMS1117_SOT-223</a> &middot; <a href=ams1117-to252.kicad_mod>AMS1117_TO-252</a> &middot; <a href=ams1117-so8.kicad_mod>AMS1117_SO-8</a></td></tr>
<tr><td class=tool style="color:#64abff">3D models</td><td>SOT-223 <a href=ams1117-sot223.step>.step</a> / <a href=ams1117-sot223.glb>.glb</a> &middot; TO-252 <a href=ams1117-to252.step>.step</a> / <a href=ams1117-to252.glb>.glb</a> &middot; SO-8 <a href=ams1117-so8.step>.step</a> / <a href=ams1117-so8.glb>.glb</a></td></tr>
<tr><td class=tool style="color:#8c6bf7">Canonical</td><td><a href=ams1117.adom-lbr.json>ams1117.adom-lbr.json</a></td></tr>
<tr><td class=tool style="color:#484f58">Fusion 360 / EAGLE</td><td class=na>Not available yet</td></tr>
<tr><td class=tool style="color:#484f58">Altium</td><td class=na>Not available yet</td></tr>
</tbody></table>

<h2>Implementation</h2>
<ul class=ul>
<li><a href="https://wiki.adom.inc/adom/ams1117-3v3-molecule"><b>AMS1117-3.3 Molecule</b></a>. A 5 V &rarr; 3.3 V regulator brick: AMS1117-3.3 in SOT-223 with 10 &micro;F input and 22 &micro;F output decoupling on a machine-pin carrier.</li>
<li><a href="https://wiki.adom.inc/adom/umw-ams1117"><b>1 A Low-Dropout Regulator UMW - AMS1117</b></a>. The second-source part. Different voltage lineup, different third package, different limits.</li>
</ul>

<h2>Application notes</h2>
<ul class=ul>
<li><b>The 22 &micro;F output capacitor is compensation, not decoupling.</b> The AMS1117 loop depends on it; a solid tantalum 22 &micro;F guarantees stability across all operating conditions. Bypassing the adjust pin improves ripple rejection but raises the output-capacitor requirement.</li>
<li><b>No protection diodes needed.</b> Internal resistors limit the adjust-pin current paths, so no diode from ADJ to output or input is required. A diode from output to input is only recommended when C<sub>OUT</sub> is large (1000 to 5000 &micro;F) and the input can be shorted; the internal diode already handles 50 to 100 A microsecond surges.</li>
<li><b>Kelvin the divider, not the load.</b> On the adjustable version, connect the top of R1 to the regulator case rather than the load, so parasitic line resistance is not multiplied by (R2+R1)/R1. Fixed versions Kelvin the top of R1 internally, so the ground pin can do negative-side sensing.</li>
<li><b>Adjust-pin bypassing.</b> For proper ripple rejection the adjust-pin capacitor's impedance at the ripple frequency must be below R1 (typically 100 to 200 &Omega;). With R1 = 100 &Omega; that is &gt;13 &micro;F at 120 Hz, but only 0.16 &micro;F at 10 kHz.</li>
<li><b>Adjustable output:</b> V<sub>OUT</sub> = V<sub>REF</sub>(1 + R2/R1) + I<sub>ADJ</sub>R2, with V<sub>REF</sub> = 1.25 V and I<sub>ADJ</sub> &asymp; 55 &micro;A. The I<sub>ADJ</sub> term is small and constant and can usually be ignored.</li>
</ul>

<h2>Datasheet</h2>
<iframe class=dsheet loading=lazy title="AMS1117 datasheet (Advanced Monolithic Systems)" src="https://wiki.adom.inc/api/v1/pages/adom/ams-ams1117/files/docs/ams1117-datasheet-ams.pdf"></iframe>
<p style="margin:8px 0 0;font-size:13px"><a href=docs/ams1117-datasheet-ams.pdf>Download the full datasheet (PDF)</a> &middot; Advanced Monolithic Systems, <i>AMS1117 1 A Low Dropout Voltage Regulator</i> &middot; <a href="http://www.advanced-monolithic.com/pdf/ds1117.pdf">advanced-monolithic.com</a></p>

<h2>Provenance</h2>
<ul class=ul>
<li><b>Every electrical number on this page</b> is read from the Advanced Monolithic Systems datasheet embedded above. Features and ordering from page 1, limits from the Electrical Characteristics tables on pages 2 to 3, application and thermal guidance from pages 4 to 5, package dimensions from pages 7 to 8. Nothing from any second source is mixed in.</li>
<li><b>Symbols:</b> generated with <code>adom-symbol</code> to the datasheet pin connections (3-pin fixed/adjustable version, and the 8-lead SOIC pinout).</li>
<li><b>Footprints:</b> the KiCad 10 official library land patterns, renamed: <code>SOT-223-3_TabPin2</code>, <code>TO-252-3_TabPin2</code> and <code>SOIC-8_3.9x4.9mm_P1.27mm</code>. The <code>TabPin2</code> variants are the correct choice here because the AMS1117 tab is V<sub>OUT</sub>, which is pin 2.</li>
<li><b>3D models:</b> the matching KiCad 10 official STEP models (<code>SOT-223.step</code>, <code>TO-252-3_TabPin2.step</code>, <code>SOIC-8_3.9x4.9mm_P1.27mm.step</code>), converted to GLB with <code>step2glb</code>.</li>
<li><b>Canonical JSON:</b> <code>ams1117.adom-lbr.json</code>, imported from the KiCad symbol + SOT-223 footprint with <code>adom-lbr import-kicad</code>.</li>
<li><b>The SCSI note</b> draws on the datasheet's own applications list plus the SCSI-2 active-termination literature (Linear Technology Design Note 34, which uses an LT1117-2.85 for exactly this).</li>
<li><b>Fusion and Altium libraries are deliberately absent.</b> They are generated rather than hand-verified, and the generated Altium symbol encoding has produced wrong geometry before, so nothing is shipped here until it can be checked in the tool itself.</li>
</ul>

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