The **LNBH25LS** is a monolithic voltage regulator and interface IC, specifically designed to power and control a Low Noise Block (LNB) down-converter in satellite TV receivers (like set-top boxes). Below is a detailed breakdown of its electronic components and functional parts. --- ### 1. Key Technical Specifications | Parameter | Value/Description | | :--- | :--- | | **Input Voltage Range** | 8V to 15V | | **Output Current** | Up to 450mA (continuous) | | **Output Voltage Steps** | 13.1V, 13.3V, 18.1V, 18.2V (via I2C) | | **Interface** | I2C Protocol (Fast mode up to 400kHz) | | **Package** | QFN24 (4x4 mm) | --- ### 2. Functional Electronic Blocks #### A. Step-up DC-DC Converter The LNBH25LS features a built-in switching controller. Since the input voltage is typically 12V, but the LNB requires up to 18V or 19V for horizontal polarization, this block "boosts" the voltage. * **External Components:** Requires an inductor, a Schottky diode, and electrolytic capacitors to complete the circuit. #### B. Linear Regulator (Post-Regulator) After the voltage is boosted, a low-drop linear regulator stabilizes the output. * **Function:** It filters out high-frequency noise from the DC-DC converter to ensure a clean signal for the satellite dish. * **Voltage Selection:** Managed via I2C to switch between 13V (Vertical) and 18V (Horizontal). #### C. DiSEqC™ Interface (Digital Satellite Equipment Control) This is the communication "brain" that talks to the satellite dish. * **22kHz Tone Generator:** It generates a 22kHz square wave signal. * **Modulation:** The tone is superimposed on the DC output voltage to send commands to the LNB (e.g., switching frequency bands). * **Tone Detector:** It can also receive 22kHz signals coming back from the LNB. #### D. Protection & Diagnostic Circuits The IC is packed with "safety" parts to prevent the set-top box from burning out: 1. **Current Limiter:** Protects against short circuits in the coaxial cable. 2. **Thermal Shutdown:** Shuts the chip off if it exceeds safe operating temperatures. 3. **Over-current Flag:** Sends a signal to the main processor via I2C if the LNB is drawing too much power. --- ### 3. Application Circuit Example (Simplified) ```mermaid graph LR Input[12V DC Input] --> Boost[DC-DC Step-Up] Boost --> Linear[Linear Regulator] I2C[MCU/I2C Control] --> Linear Linear --> Tone[22kHz Tone Injector] Tone --> Output[LNB Output / Coaxial] ``` --- ### 4. Pins and Connectivity * **VCC:** Main supply input. * **SCL/SDA:** I2C clock and data lines for communication with the main CPU. * **LX:** Connection point for the external power inductor. * **VUP:** Boosted voltage feedback pin. * **BYP:** Bypass pin for internal ripple filter. ---