L4971 is ST company's 1.5A high efficiency DC-DC converter, working in fixed frequency continuous mode. This application note introduces the internal design and application circuits of this device, including power supply voltage, output voltage, limiting circuit, temperature shutdown and other circuit design
The document provides an introduction and device description for the L4971 monolithic dc-dc converter. It details the internal building blocks, including the power supply, oscillator with voltage feed forward, current protection mechanisms (pulse by pulse and hiccup modes), soft-start functions, and feedback disconnection features.
The guide covers typical application design procedures, offering specific instructions on selecting input capacitors, output voltage dividers, inductors, and output capacitors. It also includes information on compensation networks, error amplifiers, LC filters, PWM gain, and voltage divider leading networks to ensure stable operation.
| Output current | 1.5 A |
|---|---|
| Operating input voltage range | 8 V to 55 V |
| Fixed output voltage | 3.3 V +1% |
| Adjustable output voltage range | up to 40 V |
| Pulse by pulse limiting current threshold | 2.5 A typ. |
The switching frequency (Fsw) in KHz is calculated using a resistor (Rosc) and capacitor (Cosc) with the formula: Fsw = 1 / ((Rosc * Cosc) * ln(8) + 100 - Cosc).
The device is available in two plastic packages: DIP8 and SO16L.
It uses a hiccup protection mode where the delivered average output current decreases dramatically at very low values once the limiting threshold is reached.