Power Conditioner for APL Field Devices

The LT8440 is a power conditioner for intrinsically safe, industrial ethernet ports in hazardous or explosive environments. The internal pass transistor is normally fully enhanced to deliver power to the load efficiently. In case of load circuit failures, the FET is modulated to limit the power to less than 650mW if line voltage ≤ 18.5V or less than 35mA if line voltage > 18.5V. The internal shunt transistor draws current parallel with the load up to the 500mW minimum guaranteed for Class A load power ports in compliance with Advanced Physical Layer (APL) standard or to 20mA minimum guaranteed if line voltage > 18.5V. The line voltage is sensed with two input pins that are insensitive to polarity, which can be connected in front of the port rectifier and incorporate the rectifier power consumption in the limitation of total power. The line current is measured as a voltage across the internal sense resistor, and the shunt current and the current limit are automatically adjusted for line voltage.

The LT8440 is packaged in an 8-lead SOIC with pin spacing that satisfies the device under coating specification so that shorts from pin to pin are countable faults when the circuit is examined for intrinsic safety at the highest levels of protection.

APPLICATIONS

* Industrial Ethernet

* Advanced Physical Layer

* Current Limiting

* 650mW Power Limit for Intrinsic Safety Thermal Rating when Line Voltage ≤ 18.5V

* 35mA Current Limit if Line Voltage > 18.5V

* 55mA Current Limit for APL Class A Devices

* Shunt Regulator for Mitigating Load Changes

* Guaranteed 20mA Rectifier Current for Signal Integrity