SPX3819M5-L-5-0/TR

The SPX3819M5-L-5-0/TR is a 500mA low-noise low-dropout voltage regulator from MaxLinear’s SPX3819 family, providing a fixed 5.0V output with ±1% accuracy. Originally designed by Sipex Corporation (later Exar, now MaxLinear), the device features a low dropout voltage of 340mV at full 500mA load and ultra-low quiescent current of 90µA at 100mA output. A reference bypass pin (BYP) enables output noise as low as 40µVRMS when used with an external capacitor, making it suitable for noise-sensitive analog and RF applications. The logic-compatible enable pin allows the regulator to be switched off, reducing power consumption to near zero. Comprehensive protection includes reverse battery protection, current limiting (800mA typical), and thermal shutdown. The SOT-23-5 package provides a compact footprint for space-constrained designs.

Regulation Loop

The SPX3819 uses a PMOS pass transistor driven by an error amplifier that compares the output voltage (via an internal resistor divider for fixed-voltage versions) with an internal bandgap reference. The PMOS topology enables low dropout operation since the pass element operates as a variable resistor rather than a constant-current source, minimizing the voltage differential required between input and output.

Enable and Shutdown

The EN pin provides logic-level on/off control. When EN is above 2.0V, the regulator is enabled. When EN is below 0.4V, the pass transistor is turned off and ground current drops to near zero, effectively disabling the output. This enables power sequencing and battery conservation in portable systems.

Noise Reduction via Bypass

The BYP pin connects to the internal bandgap reference through a high-impedance node. A 10nF capacitor from BYP to GND filters reference noise, reducing output noise from 300µVRMS to 40µVRMS (10Hz-100kHz). The capacitor also slows the output ramp-up rate, which may be beneficial or detrimental depending on the application’s startup timing requirements.

Protection Mechanisms

Current limiting activates at approximately 800mA, protecting the device and downstream circuitry from short-circuit faults. Thermal shutdown disables the output when the junction temperature exceeds approximately 160°C. Reverse battery protection prevents damage when the input polarity is reversed.

• Battery-powered portable devices requiring efficient 5V regulation with minimal dropout and ultra-low quiescent current
• Low-noise sensor and analog circuits where BYP capacitor reduces output noise to 40µVRMS
• Cordless phones and radio control systems needing reverse battery protection and enable-controlled power
• Post-regulation for switching converters leveraging 70dB PSRR to suppress switching ripple
• Embedded systems with power sequencing using the enable pin for controlled startup order