The LM3940ISX-3.3 from Texas Instruments is a 1A low-dropout regulator specifically designed for 5V to 3.3V conversion in a DDPAK\/TO-263-3 surface-mount package. With 500mV typical dropout, 4.5-5.5V input range, and built-in thermal and short-circuit protection, it provides a simple single-component 3.3V supply from a 5V rail.<\/p>\n
| Output Voltage<\/td>\n | 3.3V fixed<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| \u8f93\u51fa\u7535\u6d41<\/td>\n | 1A<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| \u8f93\u5165\u7535\u538b\u8303\u56f4<\/td>\n | 4.5V to 5.5V (7.5V abs max)<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| Dropout Voltage<\/td>\n | 500mV typical @ 1A; 1V max @ 1A<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| Output Accuracy<\/td>\n | +\/-3% over temperature<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| \u9759\u6001\u7535\u6d41<\/td>\n | 10-15 mA typical @ 1A<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| Line Regulation<\/td>\n | 50 mV max<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| Load Regulation<\/td>\n | 50 mV max<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| Minimum Output Capacitor<\/td>\n | 33uF (ESR critical, see ESR chart)<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| Thermal Shutdown<\/td>\n | Yes (internal)<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| Short-Circuit Protection<\/td>\n | Yes (internal current limit)<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| \u5de5\u4f5c\u6e29\u5ea6<\/td>\n | -40 to +125 C (junction)<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| \u5305\u88c5<\/td>\n | DDPAK\/TO-263-3 (10.2 x 8.4 mm)<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||
| Status<\/td>\n | \u6d3b\u8dc3<\/td>\n<\/tr>\n<\/table>\n\u7279\u70b9<\/h2>\n\u5e94\u7528<\/h2>\nProduct Overview The LM3940ISX-3.3 from Texas Instruments is a 1A low-dropout regulator specifically designed for 5V to 3.3V conversion in a DDPAK\/TO-263-3 surface-mount package. With 500mV typical dropout, 4.5-5.5V input range, and built-in thermal and short-circuit protection, it provides a simple single-component 3.3V supply from a 5V rail. Key Specifications Output Voltage 3.3V fixed Output […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[31,13],"tags":[],"chip_brand":[138],"class_list":["post-5466","post","type-post","status-publish","format-standard","hentry","category-dc-dc-converters","category-integrated-circuits-ics","chip_brand-ti"],"acf":{"brief_explanation":"1A LDO, 5V-to-3.3V, 500mV dropout, TO-263-3","date_code":"","package_case":"DDPAK\/TO-263-3 (10.2 x 8.4 x 4.4 mm)","in_stock":6904,"datasheet":"https:\/\/www.ti.com\/lit\/ds\/symlink\/lm3940.pdf","price":"$0.72 @ 1ku","product_introduction":"The LM3940ISX-3.3 from Texas Instruments is a 1A low-dropout linear regulator purpose-designed for converting a 5V supply to 3.3V in a DDPAK\/TO-263-3 surface-mount package. The ISX denotes the TO-263-3 (DDPAK) package with tape and reel (500 pcs\/reel), -3.3 denotes the 3.3V fixed output. Unlike general-purpose LDOs with wide input ranges, the LM3940 is optimized specifically for the 4.5-5.5V input to 3.3V output use case, with a guaranteed minimum input voltage of 4.5V. The 500mV typical dropout at 1A means the device maintains 3.3V regulation down to approximately 3.8V input. The regulator requires only a single 33uF output capacitor as external component, though the capacitor ESR must be within a specified stability window (typically 0.1-10 Ohms at 1A). The TO-263\/DDPAK package provides excellent thermal dissipation when soldered to a copper plane on the PCB, often eliminating the need for a separate heatsink at moderate ambient temperatures. Internal thermal shutdown and short-circuit current limiting provide robustness. Also available in SOT-223 (LM3940IMP-3.3) and TO-220 packages.","working_principle":"The LM3940ISX-3.3 operates as a series-pass linear regulator: (1) Pass Element: An internal PNP transistor (or PNP-NPN composite) is connected between VIN and VOUT. The error amplifier drives the base of the pass transistor to maintain VOUT at 3.3V. The PNP structure enables the low dropout voltage (500mV) because the base can be driven lower than VOUT by the error amplifier, unlike NPN-based regulators that require at least 1.5-2V headroom. (2) Voltage Regulation: The error amplifier compares a fraction of VOUT (via an internal resistor divider) with an internal bandgap reference. If VOUT drops below 3.3V, the amplifier increases the pass transistor drive current, reducing VCE and raising VOUT. If VOUT rises above 3.3V, the amplifier reduces drive current. (3) Dropout Behavior: When VIN approaches 3.3V + Vdropout, the pass transistor saturates and can no longer regulate. The output then tracks VIN minus the saturation voltage drop. At 1A load, this dropout is typically 500mV. (4) Stability: The output capacitor and its ESR create a zero in the loop transfer function that is essential for stability. The ESR must be in a specific range (typically 0.1-10 Ohms at full load) to ensure adequate phase margin. Solid tantalum capacitors are recommended for their stable ESR over temperature.","pin_description":"
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