Three extra features previously unavailable in controllers for IEEE 802.3af Powerover-Ethernet (PoE) power-sourcing-equipment (PSE) make Maxim's MAX5945 unique. As the PoE specification requires, the quad controller provides discovery, classification, current limit, and dc and ac load disconnect detection to a powered device (PD). It also can operate autonomously or be controlled by software through an I2C-compatible interface.
The novel features include cadence-timing, which allows the MAX5945 to be used in midspan systems as well as in switch/router PSE applications. In addition, the controller's watchdog feature lets system hardware gracefully assume control if the system software crashes. Finally, besides the standard version of the controller, which is guaranteed over the commercial 0°C to 70°C range, another version fits the extended –40°C to 85°C range.
Standard capabilities include programmable gate charging current, current-limit threshold, startup timeout, overcurrent timeout, and auto restart duty-cycle. A classovercurrent detection function lets the system determine if a PD is drawing more current than allowed for its class. Other standard features include input undervoltage and overvoltage lockout, output-voltage slew-rate limit, overtemperature protection, powergood, and fault status outputs.
The MAX5945 comes in a 36-pin SSOP. Prices start at $6.81 in quantities of 1000 units and up.
Maxim Semiconductor
www.maxim-ic.com