**LT8301IS5#TRPBF: A Comprehensive Technical Overview and Application Guide**

The **LT8301IS5#TRPBF** from Analog Devices is a highly integrated, monolithic **flyback converter** designed to simplify isolated power supply design. This component excels in extracting power directly from the primary-side flyback waveform, eliminating the need for a third transformer winding or an opto-isolator for feedback. This article provides a detailed technical breakdown and practical guidance for its implementation.

**Technical Deep Dive: Core Architecture and Operation**

At its heart, the LT8301 is a **current-mode switching regulator**. Its most significant innovation is its unique output voltage sensing mechanism. It samples the voltage of the flyback waveform during the switch's off-time, which appears across the primary-side leakage inductance and the primary winding itself. This sampled voltage is directly proportional to the output voltage, scaled by the transformer's turns ratio (N).

The device features an integrated **150 V, 350 mΩ power MOSFET**, which significantly reduces the external component count and simplifies board layout. Operating at a switching frequency of up to 250 kHz, it allows for the use of small magnetics. The converter enters **Burst Mode® operation** under light-load conditions, minimizing quiescent current and maintaining high efficiency across a wide load range.

Key specifications include:

* **Wide Input Voltage Range:** 4.5V to 42V (60V abs max)

* **Precision Feedback Reference:** 1.225V

* **Programmable Soft-Start**

* **Frequency Foldback** for short-circuit protection

* **Thermal Shutdown**

**Application Guide: Designing an Isolated Power Supply**

Designing with the LT8301 revolves around the selection of three key external components: the transformer, the output capacitor, and a few resistors.

1. **Transformer Selection and Design:** The transformer is the most critical component. The turns ratio (N = Np/Ns) must be chosen based on the input voltage range and desired output voltage (Vout). The relationship is defined by Vout ≈ (Vout_sense * N) / R, where Vout_sense is the internal reference (1.225V). The primary inductance (Lp) is chosen to set the desired operating mode (boundary or discontinuous conduction) and ripple current.

2. **Setting the Output Voltage:** The output voltage is programmed using a single external resistor (Rfb) connected between the Vc pin and ground. The value is calculated using the formula: **Vout = 1.225V * (N) * (1 + Rfb / 10.4kΩ)**. This simplicity is a major advantage of the primary-side regulation scheme.

3. **Output Capacitor:** A low-ESR capacitor is recommended on the output to minimize voltage ripple. The value depends on the load current and the allowable ripple.

4. **Layout Considerations:** As with any high-frequency switching regulator, proper PCB layout is crucial. The loop containing the input capacitor, transformer primary, and the internal MOSFET switch must be as small as possible to minimize EMI and voltage spikes. A ground plane is highly recommended for stability.

**Typical Use Cases**

The LT8301 is ideal for applications requiring isolated power from a non-isolated source. Common applications include:

* Isolated bias supplies for industrial systems, data acquisition, and telecom hardware.

* Automotive and battery-powered systems requiring rugged, efficient conversion.

* Providing isolated gate drive power for motor control circuits and half/full-bridge configurations.

**ICGOODFIND**

The **LT8301IS5#TRPBF** stands out as an exceptionally simple and robust solution for low-to-moderate power isolated DC/DC conversion. Its primary-side regulation architecture, which **eliminates the opto-coupler and auxiliary winding**, dramatically reduces component count, design complexity, and board space. With its **integrated high-voltage switch** and wide operating range, it offers designers a reliable and highly efficient path to creating compact, high-performance isolated power supplies.

**Keywords:**

1. **Flyback Converter**

2. **Primary-Side Regulation**

3. **Isolated Power Supply**

4. **Integrated MOSFET**

5. **Burst Mode Operation**