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MAX5988A/MAX5988B

IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2,

Powered Devices with Integrated DC-DC Converter

19-6476; Rev 2; 4/14

General Description

The MAX5988A/MAX5988B 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-drop-

out 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 isola-

tion 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 volt-

age range from 8.8V to 60V and supports up to 6.49W of

input power at 1.3A load. The DC-DC converter operates

at a fixed 215kHz 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 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.

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.

Applications

IEEE 802.3af-Powered Devices

IP Phones

Wireless Access Nodes

IP Security Cameras

WiMAX

Base Stations

Features

S IEEE 802.3af Compliant

S PoE Class 1/Class 2 Classification

S Sleep and Ultra-Low-Power Mode

S Intelligent Maintain Power Signature (MPS)

S Simplified Wall Adapter Interface

S Efficient, Integrated DC-DC Converter (with

Integrated Switches)

S 8.8V to 60V Wide Input Voltage Range

S 3.0V to 14V Programmable Output Voltage Range

S Internal Compensation

S Fixed 215kHz 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

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 Fixed 3.3V or Adjustable Output Voltage Through

an External Resistive Divider (LDO)

S 49mA (typ) Inrush Current Limit

S Pass 2kV, 200m CAT-6 Cable Discharge Event

Ordering Information/Selector Guide appears at end of data

sheet.

For related parts and recommended products to use with this part,

refer to www.maximintegrated.com/MAX5988A.related.

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.

EVALUATION KIT AVAILABLE

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

Summary of content (21 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter General Description The MAX5988A/MAX5988B provide a complete powersupply 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.
PAGE 2
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter ABSOLUTE MAXIMUM RATINGS (All voltages referenced to GND, unless otherwise noted.) VDD to GND...........................-0.3V to +70V (internally clamped) (100V, 100ms, RTEST = 3.3kω) (Note 1) VCC, WAD, RREF to GND......................... -0.3V to (VDD + 0.3V) AUX, LDO_IN, LED to GND..................................... -0.3V to 16V LDO_OUT to GND............................... -0.
PAGE 3
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter ELECTRICAL CHARACTERISTICS (continued) (VDD = 48V, RSIG = 24.9kω, LED, VCC, SL, ULP, WK, RESET, LDO_OUT unconnected, WAD = LDO_EN = LDO_IN = PGND = GND, C1 = 68nF, C2 = 10µF, C3 = 1µF (see Figure 3), VFB = VAUX = 0V, LX unconnected, CLASS2 = 0V, MPS = 0V. All voltages are referenced to GND, unless otherwise noted. TA = TJ = -40°C to +85°C, unless otherwise noted.
PAGE 4
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter ELECTRICAL CHARACTERISTICS (continued) (VDD = 48V, RSIG = 24.9kω, LED, VCC, SL, ULP, WK, RESET, LDO_OUT unconnected, WAD = LDO_EN = LDO_IN = PGND = GND, C1 = 68nF, C2 = 10µF, C3 = 1µF (see Figure 3), VFB = VAUX = 0V, LX unconnected, CLASS2 = 0V, MPS = 0V. All voltages are referenced to GND, unless otherwise noted. TA = TJ = -40°C to +85°C, unless otherwise noted.
PAGE 5
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter ELECTRICAL CHARACTERISTICS (continued) (VDD = 48V, RSIG = 24.9kω, LED, VCC, SL, ULP, WK, RESET, LDO_OUT unconnected, WAD = LDO_EN = LDO_IN = PGND = GND, C1 = 68nF, C2 = 10µF, C3 = 1µF (see Figure 3), VFB = VAUX = 0V, LX unconnected, CLASS2 = 0V, MPS = 0V. All voltages are referenced to GND, unless otherwise noted. TA = TJ = -40°C to +85°C, unless otherwise noted.
PAGE 6
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter ELECTRICAL CHARACTERISTICS (continued) (VDD = 48V, RSIG = 24.9kω, LED, VCC, SL, ULP, WK, RESET, LDO_OUT unconnected, WAD = LDO_EN = LDO_IN = PGND = GND, C1 = 68nF, C2 = 10µF, C3 = 1µF (see Figure 3), VFB = VAUX = 0V, LX unconnected, CLASS2 = 0V, MPS = 0V. All voltages are referenced to GND, unless otherwise noted. TA = TJ = -40°C to +85°C, unless otherwise noted.
PAGE 7
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter ELECTRICAL CHARACTERISTICS (continued) (VDD = 48V, RSIG = 24.9kω, LED, VCC, SL, ULP, WK, RESET, LDO_OUT unconnected, WAD = LDO_EN = LDO_IN = PGND = GND, C1 = 68nF, C2 = 10µF, C3 = 1µF (see Figure 3), VFB = VAUX = 0V, LX unconnected, CLASS2 = 0V, MPS = 0V. All voltages are referenced to GND, unless otherwise noted. TA = TJ = -40°C to +85°C, unless otherwise noted.
PAGE 8
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) QUIESCENT CURRENT vs. SUPPLY VOLTAGE (ULTRA-LOW POWER MODE) 0.35 0.30 0.25 0.20 0.15 0.10 3.50 3.25 3.00 2.75 0 2.9 4.4 5.9 7.4 8.9 2.50 10.1 27 26 25 24 23 22 40 35 45 50 55 1.4 60 2.9 4.4 5.9 7.4 8.9 INPUT VOLTAGE (V) SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) INPUT OFFSET CURRENT vs.
PAGE 9
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) VIN = 36V EFFICIENCY (%) 90 90 85 80 VIN = 48V 75 VIN = 36V VIN = 48V 95 EFFICIENCY (%) VIN = 12V 95 100 MAX5988A toc10 100 EFFICIENCY vs. LOAD CURRENT (MAX5988B, VOUT = 12V) VIN = 57V 80 75 70 65 65 60 VIN = 57V 85 70 60 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 0.1 0.
PAGE 10
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Pin Configuration WK LDO_FB RESET MPS CLASS2 TOP VIEW 15 14 13 12 11 WAD 16 VDD 17 MAX5988A MAX5988B VCC 18 PGND 19 3 4 5 LDO_IN LDO_OUT 1 AUX 2 LED + LX RREF 20 *EP 10 ULP 9 SL 8 VDRV 7 GND 6 FB TQFN 4mm × 4mm *EXPOSED PAD, CONNECT EP TO GND. Pin Description PIN NAME 1 AUX 2 LX 3 LED LED Driver Output.
PAGE 11
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Pin Description (continued) PIN NAME FUNCTION 7 GND Ground. Reference rail for the device. It is also the “quiet” ground for all voltage references (e.g., FB is referenced to this GND). 8 VDRV Internal 5V Regulator Voltage Output. The internal voltage regulator provides 5V to the MOSFET driver and other internal circuits. VDRV is referenced to GND.
PAGE 12
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Detailed Description PD Interface The MAX5988A/MAX5988B include complete interface functions for a PD to comply with the IEEE 802.3af standard as a Class 1/Class 2 PD. The devices provide the detection and classification signatures using a single external signature resistor. An integrated MOSFET provides isolation from the buck converter when the PSE has not applied power.
PAGE 13
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Sleep and Ultra-Low-Power Modes The devices feature a sleep mode and an ultra-lowpower mode in which the internal p-channel isolation MOSFET is kept on and the buck regulator is off. In sleep mode, the LED driver output (LED) pulse width modulates the LED current with a 25% duty cycle. The peak LED current (ILED) is set by an external resistor R SL.
PAGE 14
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Frequency Foldback Protection for High-Efficiency Light-Load Operation The devices enter frequency foldback mode when eight consecutive inductor current zero-crossings occur. The switching frequency is 215kHz under loads large enough that the inductor current does not cross zero. In frequency foldback mode, the switching frequency is reduced to 107.
PAGE 15
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter VCC Input Capacitor Selection The input capacitor reduces the current peaks drawn from the input power supply and reduces switching noise in the IC.
PAGE 16
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter PCB Layout Careful PCB layout is critical to achieve clean and stable operation. It is highly recommended to duplicate the MAX5988A EV kit layout for optimum performance. If deviation is necessary, follow these guidelines for good PCB layout: 1) Connect input and output capacitors to the power ground plane; connect all other capacitors to the signal ground plane.
PAGE 17
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Typical Application Circuits RJ45 AND BRIDGE RECTIFIER C1 68nF 2.2µF VDD C2 10µF VCC WAD AUX VDRV L0 47µH CLASS2 C3 1µF LDO_FB WK TO µP OPEN-DRAIN OUTPUTS OR PULLDOWN SWITCHES R1 7.5kI MAX5988A MAX5988B ULP C4 100µF FB SL R2 2.49kI RSL 60.4kI TO 5V OUTPUTS 5V OUTPUT LX MPS LDO_IN LDO_OUT C5 1µF C6 1µF LED RREF RSIG 24.9kI 3.
PAGE 18
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Typical Application Circuits (continued) RJ45 AND BRIDGE RECTIFIER C1 68nF 2.2µF VDD C2 10µF VCC WAD AUX VDRV L0 47µH CLASS2 C3 1µF R1 7.5kI MAX5988A MAX5988B WK TO µP OPEN-DRAIN OUTPUTS OR PULLDOWN SWITCHES 5V OUTPUT LX MPS ULP C4 100µF FB R2 2.49kI SL RSL 60.4kI ADJ_LDO_OUT LDO_OUT R3 TO 5V OUTPUTS LDO_IN C5 1µF R4 RREF RSIG 24.
PAGE 19
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Functional Diagram MAX5988A MAX5988B VCC VDD 5V TVS HOT-SWAP CONTROLLER DETECTION CLASSIFICATION GND 5V RREF WAD PD VOLTAGE MONITOR AUX 5V 5V 1.
PAGE 20
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Package Information Chip Information PROCESS: BiCMOS For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
PAGE 21
MAX5988A/MAX5988B IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2, Powered Devices with Integrated DC-DC Converter Revision History REVISION NUMBER REVISION DATE 0 11/12 Initial release — 1 1/13 Corrected land pattern number 20 2 4/14 Updated pin 16 in Pin Description table 11 DESCRIPTION PAGES CHANGED Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied.