The MAX5991A/MAX5991B provide a complete power-supply solution as IEEE®802.3af-compliant Class 1/Class 2 Powered Devices (PDs) in a Power-over-Ethernet (PoE) system. The devices integrate the PD interface with an efficient DC-DC converter, offering a low external part count PD solution. The devices also include a low-dropout regulator, MPS, sleep, and ultra-low power modes.The PD interface provides a detection signature and a Class 1/Class 2 classification signature with a single external resistor. The PD interface also provides an isolation power MOSFET, a 60mA (max) inrush current limit, and a 321mA (typ) operating current limit.The integrated step-down DC-DC converter uses a peak current-mode control scheme and provides an easy-to-implement architecture with a fast transient response. The step-down converter operates in a wide input voltage range from 8.7V to 60V and supports up to 6.49W of input power at 1.3A load. The DC-DC converter operates at a fixed 430kHz switching frequency, with an efficiency-boosting frequency foldback that reduces the switching frequency by half at light loads.The devices feature an input undervoltage-lockout (UVLO) with wide hysteresis and long deglitch time to compensate for twisted-pair cable resistive drop and to assure glitch-free transition during power-on/-off conditions. The devices also feature overtemperature shutdown, short-circuit protection, output overvoltage protection, and hiccup current limit for enhanced performance and reliability.All devices are available in a 20-pin, 4mm × 4mm, TQFN power package and operate over the -40°C to +85°C temperature range.ApplicationsIEEE 802.3af-Powered DevicesIP PhonesIP Security CamerasWireless Access Nodes