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LM3940ISX-3.3

1A LDO, 5V-to-3.3V, 500mV dropout, TO-263-3

6904

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Pieza del fabricante：

LM3940ISX-3.3

Paquete：

DDPAK/TO-263-3 (10.2 x 8.4 x 4.4 mm)

Marca：
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Descripción

Productos

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.

Especificaciones

Output Voltage 3.3V fixed
Corriente de salida 1A
Input Voltage Range 4.5V to 5.5V (7.5V abs max)
Dropout Voltage 500mV typical @ 1A; 1V max @ 1A
Output Accuracy +/-3% over temperature
Corriente de reposo 10-15 mA typical @ 1A
Line Regulation 50 mV max
Load Regulation 50 mV max
Minimum Output Capacitor 33uF (ESR critical, see ESR chart)
Thermal Shutdown Yes (internal)
Short-Circuit Protection Yes (internal current limit)
Temperatura de funcionamiento -40 to +125 C (junction)
Paquete DDPAK/TO-263-3 (10.2 x 8.4 mm)
Status Activo

Características

  • Purpose-designed for 5V to 3.3V conversion
  • 1A output current with true low dropout
  • Only one external component (33uF output capacitor)
  • Built-in thermal shutdown protection
  • Short-circuit current limiting
  • Output voltage specified over full temperature range
  • TO-263/DDPAK surface-mount package for efficient thermal dissipation

Aplicaciones

  • 5V to 3.3V logic level conversion
  • Desktop and laptop computer 3.3V rails
  • Mixed 5V/3.3V system power supplies
  • Industrial controller 3.3V regulation from 5V bus

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.

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 Nombre Tipo Descripción
1 VIN Potencia Input voltage (4.5-5.5V)
2 GND Potencia Ground (tab and pin)
3 VOUT Potencia Regulated 3.3V output
Pestaña GND Potencia Ground / thermal pad (connected to pin 2)
  • 5V to 3.3V logic supply conversion at 1A with only a 33uF tantalum output capacitor and TO-263 copper plane heatsink
  • Laptop computer 3.3V rail from 5V system supply with guaranteed regulation down to 4.5V input
  • Industrial controller 3.3V MCU supply from 5V bus with thermal shutdown protection and short-circuit current limiting
  • Embedded system 5V/3.3V dual-rail design using LM3940 for the 3.3V rail with 500mV dropout headroom
Modelo Fabricante Vout Iout Notas
LM3940IMP-3.3 TI 3.3V 1A SOT-223 package
AMS1117-3.3 Advanced Monolithic 3.3V 1A Popular, 1.1V dropout
LD1117S33CTR STMicro 3.3V 800mA Similar, TO-263
TLV1117LV33DCYR TI 3.3V 1A Lower Iq, SOT-223
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Materialparts is a professional electronic component supplier based in Shenzhen, China, with over 20 years of global trading experience. We integrate component procurement, quality inspection, technical support, customized packaging, and global delivery services to provide one-stop supply chain solutions. Our business covers industrial control, automotive electronics, consumer electronics, medical devices and other industries. We always adhere to genuine sources, stable supply and considerate after-sales service.

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Address: Room 2919, Guoli Building, Huaqiang North, Futian District, Shenzhen, Guangdong, China
 

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