EVALUATION KIT AVAILABLE
MAX5991A/MAX5991B
IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2,
Powered Devices with Integrated DC-DC Converter
General Description
Benefits and Features
The MAX5991A/MAX5991B provide a complete power-
supply solution as IEEE 802.3af-compliant Class 1/
S IEEE 802.3af Compliant
®
S PoE Class 1/Class 2 Classification
S Intelligent Maintain Power Signature (MPS)
S Sleep and Ultra-Low Power Mode
S Simplified Wall Adapter Interface
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-drop-
out regulator, MPS, sleep, and ultra-low power modes.
S Efficient, Integrated DC-DC Converter
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 isola-
tion power MOSFET, a 60mA (max) inrush current limit,
and a 321mA (typ) operating current limit.
(with Integrated Switches)
S 8.7V to 60V Wide Input Voltage Range
S 3.2V to 14V Programmable Output Voltage Range
S Internal Compensation
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 volt-
age 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.
S Fixed 430kHz Switching Frequency
S Frequency Foldback for High-Efficiency Light-
Load Operation
S Built-In Output-Voltage Monitoring
S Open-Drain RESET Output
S Protects Against Overload, Output Short Circuit,
Output Overvoltage, and Overtemperature
S Hiccup-Mode Runaway Current Limit
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 condi-
tions. The devices also feature overtemperature shut-
down, short-circuit protection, output overvoltage protec-
tion, and hiccup current limit for enhanced performance
and reliability.
S Back-Bias Capability to Optimize the Efficiency
S Integrated TVS Diode Withstands Cable Discharge
Event (CDE)
S Internal LDO Regulator with Up to 100mA Load
S 49mA (typ) Inrush Current Limit
S Pass 2kV, 200m CAT-6 Cable Discharge Event
All devices are available in a 20-pin, 4mm x 4mm, TQFN
power package and operate over the -40°C to +85°C
temperature range.
Ordering Information appears at end of data sheet.
For related parts and recommended products to use with this part,
refer to www.maximintegrated.com/MAX5991.related.
Applications
IEEE 802.3af-Powered Devices
IP Phones
Wireless Access Nodes
IP Security Cameras
®
WiMAX Base Stations
IEEE is a registered service mark of the Institute of Electrical
and Electronics Engineers, Inc.
WiMAX is a registered certification mark and registered service
mark of WiMAX Forum.
For pricing, delivery, and ordering information, please contact Maxim Direct at
1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
19-6529; Rev 1; 1/13
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