Simplified Block Diagram
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- Powered Device Interface
- Fully Integrated IEEE 802.3af-Compliant PD Interface
- PD Detection and Programmable Classification Signatures
- Less than 10µA Leakage Current Offset During Detection
- Integrated MOSFET for Isolation and Inrush Current Limiting
- Gate Output Allows External Control of the Internal Isolation MOSFET
- Programmable Inrush Current Control
- Programmable Undervoltage Lockout (MAX5953A/MAX5953C)
- DC-DC Converter
- Clamped, Two-Switch Power IC for High Efficiency
- Integrated High-Voltage 0.4Ω Power MOSFETs Up to 15W Output Power
- Bias Voltage Regulator with Automatic High-Voltage Supply Turn-Off
- 11V to 76V Wide Input Voltage Range
- Feed-Forward Voltage-Mode Control for Fast Input Transient Rejection
- Programmable Undervoltage Lockout
- Overtemperature Shutdown
- Indefinite Short-Circuit Protection with Programmable Fault Integration
- Integrated Look-Ahead Signal for Secondary-Side Synchronous Rectification
- > 90% Efficiency with Synchronous Rectification
- Up to 500kHz Switching Frequency
- High-Power (2.22W), 7mm x 7mm Thermally Enhanced Lead-Free Thin QFN Package
- Computer Telephony
- IEEE 802.3af Powered Devices
- Internet Appliances
- IP Phones
- Security Cameras
- Wireless Access Nodes
An integrated MOSFET provides PD isolation during detection and classification. All devices guarantee a leakage current offset of less than 10µA during the detection phase. A programmable current limit prevents high inrush current during power-on. The devices feature power-mode undervoltage lockout (UVLO) with wide hysteresis and long deglitch time to compensate for twisted-pair-cable resistive drop and to assure glitch-free transition between detection, classification, and power-on/-off phases. The MAX5953A/MAX5953C have an adjustable UVLO threshold with the default value compliant to the 802.3af standard, while the MAX5953B/MAX5953D have a lower and fixed UVLO threshold compatible with some legacy pre-802.3af power-sourcing equipment (PSE) devices.
The DC-DC converters are operable in either forward or flyback configurations with a wide input voltage range from 11V to 76V and up to 15W of output power. The voltage-clamped power topology enables full recovery of stored magnetizing and leakage inductive energy for enhanced efficiency and reliability. When using the high-side MOSFET, the controller can be configured as a buck converter. A look-ahead signal for driving secondary-side synchronous rectifiers can be used to increase efficiency. A wide array of protection features include UVLO, over-temperature shutdown, and short-circuit protection with hiccup current limit for enhanced performance and reliability. Operation up to 500kHz allows for smaller external magnetics and capacitors.
The MAX5953A/MAX5953B/MAX5953C/MAX5953D are available in a high-power (2.22W), 7mm x 7mm thermally enhanced thin QFN package.