What is the LM3525?
The LM3525 is a high-side P-channel power switch that provides Universal Serial Bus standard power switching and over-current protection for all host port applications. It's designed to handle the unique challenges of USB power delivery, including hot-plug events, inrush currents, and short-circuit conditions.
The device is available in two variants:
Key Specifications
Electrical Characteristics
Absolute Maximum Ratings
| Parameter | Rating |
|---|---|
| Supply Voltage | -0.3V to 6.0V |
| Output Voltage | -0.3V to 6.0V |
| Voltage at All Other Pins | -0.3V to 5.5V |
Key Features
The LM3525 packs a impressive set of features into its small 8-pin package:
USB Compatibility
Protection Features
Over-current protection with 1A nominal short-circuit output current
Thermal shutdown protects the device during direct short conditions
Undervoltage Lockout (UVLO) prevents operation at unsafe voltages
Power Management
1ms fault flag delay prevents erroneous overcurrent reporting during hot-plug events
Wide input voltage range (2.7V to 5.5V) for 3.3V and 5V applications
Low Power Consumption
Form Factor
Pin Description
Typical Application Circuit
In a typical application, current flows through the high-side P-channel switch from IN to OUT towards the load. The enable pin (EN) controls the switch state, while the fault flag (FLG) provides status feedback to the host controller.
The LM3525 is particularly well-suited for:
1. Notebook PC and Handheld PC Applications
The single-port design is ideal for portable devices that supply power to one USB port. The 1A nominal short-circuit output current protects the notebook PC's power supplies from damaging overcurrent conditions.
2. USB Root Hubs and Self-Powered Hubs
The LM3525 accepts input voltages between 2.7V and 5.5V, allowing use as a device-based inrush current limiter for 3.3V USB peripherals, as well as root and self-powered hubs at 5.5V. The small size, low RON, and 1ms fault flag delay make it an excellent choice for root hubs and ganged power control in space-constrained self-powered hubs.
3. Hot-Plug Event Management
One of the LM3525's most valuable features is its ability to handle hot-plug events gracefully. The 1ms delay on the fault flag output prevents erroneous overcurrent reporting caused by inrush currents when a device is plugged in. This delay is adequate for most applications.
Design Considerations
Current Handling
The LM3525 is designed for 500mA continuous output current. While it can handle up to 1A during short-circuit conditions, designers should ensure their application stays within the continuous current rating.
Thermal Management
The thermal resistance (θJA) of the LM3525 in the SO-8 package is 150°C/W. At elevated temperatures, maximum power dissipation must be derated. The thermal shutdown feature will protect the device from permanent damage during fault conditions.
Logic Compatibility
The enable input accepts both 3.3V and 5.0V logic thresholds, making it compatible with a wide range of microcontrollers and host controllers.
Variants and Ordering Information
The LM3525 is available in several variants:
| Part Number | Enable Polarity | Package | Temperature Range |
|---|---|---|---|
| LM3525M-H | Active-high | SOIC-8 | -40°C to +85°C |
| LM3525MX-H | Active-high | SOIC-8 (Tape & Reel) | -40°C to +85°C |
| LM3525M-L | Active-low | SOIC-8 | -40°C to +85°C |
| LM3525MX-L | Active-low | SOIC-8 (Tape & Reel) | -40°C to +85°C |
The "/NOPB" suffix indicates lead-free (No Pb) versions.
For the latest documentation, including the full datasheet and application notes, visit TI's product page
