LT8440

The EVAL-LT8440-AZ evaluation circuit features the LT8440 used in a load power port of an intrinsically safe field device. It can regulate and limit the power drawn by the port according to the Ethernet Advanced Physical Layer (Ethernet-APL) standard. The EVAL-LT8440-AZ is designed with three LT8440s in series to meet the triple redundancy requirement of intrinsic safety Ex ia for class A field devices, but it can be configured to work with a lower LT8440 count. See the Redundancy of LT8440 section for more details.

The evaluation circuit is also equipped with filters and protection components to meet the Ethernet-APL and intrinsic safety standards, including IEC60079-11 and IEC60079-47 standards. Communication signal integrity is well preserved on this evaluation circuit, allowing seamless link up between 10BASE-T1L devices.

The EVAL-LT8440-AZ board is designed to operate from 9V to 17.5V input voltage. Across the input voltage range, the LT8440 draws current in parallel with the load up to the 500mW minimum guaranteed for Class A load power ports in compliance with Advanced Physical Layer (APL) standards. In case of load circuit failures, the evaluation board also limits input power below 650mW. The LT8440 shunts current even at no load to ensure at least 20mA input current during normal operation, which is required by APL specification for signal integrity.

Design files for this circuit board are available at Product Evaluation Boards and Kits | Design Center | Analog Devices.