Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - AC/DC converter, offline switcher Forward EN, Frequency control, Soft Start, Sync W

Active-Clamped, Spread-Spectrum,

Current-Mode PWM Controllers

MAX5974A/MAX5974B/MAX5974C/MAX5974D

EVALUATION KIT AVAILABLE

19-5331; Rev 4; 10/14

Ordering Information/Selector Guide

General Description

The MAX5974_ provide control for wide-input-voltage,

active-clamped, current-mode PWM, forward converters

in Power-over-Ethernet (PoE) powered device (PD) appli-

cations. The MAX5974A/MAX5974C are well-suited for

universal or telecom input range, while the MAX5974B/

MAX5974D also accommodate low input voltage down

to 10.5V.

The devices include several features to enhance sup-

ply efficiency. The AUX driver recycles magnetizing

current instead of wasting it in a dissipative clamp circuit.

Programmable dead time between the AUX and main

driver allows for zero-voltage switching (ZVS). Under

light-load conditions, the devices reduce the switching

frequency (frequency foldback) to reduce switching

losses.

The MAX5974A/MAX5974B feature unique circuitry to

achieve output regulation without using an optocoupler,

while the MAX5974C/MAX5974D utilize the traditional

optocoupler feedback method. An internal error amplifier

with a 1% reference is very useful in nonisolated design,

eliminating the need for an external shunt regulator.

The devices feature a unique feed-forward maximum

duty-cycle clamp that makes the maximum clamp

voltage during transient conditions independent of the

line voltage, allowing the use of a power MOSFET with

lower breakdown voltage. The programmable frequency

dithering feature provides low-EMI, spread-spectrum

operation.

The MAX5974_ are available in 16-pin TQFN-EP

packages and are rated for operation over the -40°C to

+85°C temperature range.

Features

S Peak Current-Mode Control, Active-Clamped

Forward PWM Controller

S Regulation Without Optocoupler (MAX5974A/

MAX5974B)

S Internal 1% Error Amplifier

S 100kHz to 600kHz Programmable Q8% Switching

Frequency, Synchronization Up to 1.2MHz

S Programmable Frequency Dithering for Low-EMI,

Spread-Spectrum Operation

S Programmable Dead Time, PWM Soft-Start,

Current Slope Compensation

S Programmable Feed-Forward Maximum Duty-

Cycle Clamp, 80% Maximum Limit

S Frequency Foldback for High-Efficiency Light-

Load Operation

S Internal Bootstrap UVLO with Large Hysteresis

S 100µA (typ) Startup Supply Current

S Fast Cycle-by-Cycle Peak Current-Limit, 35ns

Typical Propagation Delay

S 115ns Current-Sense Internal Leading-Edge

Blanking

S Output Short-Circuit Protection with Hiccup Mode

S Reverse Current Limit to Prevent Transformer

Saturation Due to Reverse Current

S Internal 18V Zener Clamp on Supply Input

S 3mm x 3mm, Lead-Free, 16-Pin TQFN-EP

Applications

PoE IEEE

802.3af/at Powered Devices

High-Power PD (Beyond the 802.3af/at Standard)

Active-Clamped Forward DC-DC Converters

IP Phones

Wireless Access Nodes

Security Cameras

+Denotes a lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad.

IEEE is a registered service mark of the Institute of Electrical

and Electronics Engineers, Inc.

PART TOP MARK PIN-PACKAGE TEMP RANGE

UVLO

THRESHOLD (V)

FEEDBACK MODE

MAX5974AETE+ +AHY 16 TQFN-EP* -40°C to +85°C 16 Sample/Hold

MAX5974BETE+ +AHZ 16 TQFN-EP* -40°C to +85°C 8.4 Sample/Hold

MAX5974CETE+ +AIA 16 TQFN-EP* -40°C to +85°C 16 Continuously Connected

MAX5974DETE+ +AIB 16 TQFN-EP* -40°C to +85°C 8.4 Continuously Connected

MAX5974DATE+ +AIB 16 TQFN-EP* -40°C to +125°C 8.4 Continuously Connected

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 (28 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers General Description Features The MAX5974_ provide control for wide-input-voltage, active-clamped, current-mode PWM, forward converters in Power-over-Ethernet (PoE) powered device (PD) applications. The MAX5974A/MAX5974C are well-suited for universal or telecom input range, while the MAX5974B/ MAX5974D also accommodate low input voltage down to 10.5V.
PAGE 2
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers ABSOLUTE MAXIMUM RATINGS IN to GND (VEN = 0V)............................................-0.3V to +26V EN, NDRV, AUXDRV to GND......................-0.3V to (VIN + 0.3V) RT, DT, FFB, COMP, SS, DCLMP, DITHER/SYNC to GND..................................................................-0.3V to +6V FB to GND (MAX5974A/MAX5974B only)...................-6V to +6V FB to GND (MAX5974C/MAX5974D only)...............-0.
PAGE 3
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers ELECTRICAL CHARACTERISTICS (continued) (VIN = 12V (for MAX5974A/MAX5974C, bring VIN up to 17V for startup), VCS = VCSSC = VDITHER/SYNC = VFB = VFFB = VDCLMP = VGND, VEN = +2V, NDRV = AUXDRV = SS = COMP = unconnected, RRT = 34.8kI, RDT = 25kI, CIN = 1FF, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.
PAGE 4
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers ELECTRICAL CHARACTERISTICS (continued) (VIN = 12V (for MAX5974A/MAX5974C, bring VIN up to 17V for startup), VCS = VCSSC = VDITHER/SYNC = VFB = VFFB = VDCLMP = VGND, VEN = +2V, NDRV = AUXDRV = SS = COMP = unconnected, RRT = 34.8kI, RDT = 25kI, CIN = 1FF, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS -40°C to +85°C 9.
PAGE 5
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers ELECTRICAL CHARACTERISTICS (continued) (VIN = 12V (for MAX5974A/MAX5974C, bring VIN up to 17V for startup), VCS = VCSSC = VDITHER/SYNC = VFB = VFFB = VDCLMP = VGND, VEN = +2V, NDRV = AUXDRV = SS = COMP = unconnected, RRT = 34.8kI, RDT = 25kI, CIN = 1FF, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.
PAGE 6
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers ELECTRICAL CHARACTERISTICS (continued) (VIN = 12V (for MAX5974A/MAX5974C, bring VIN up to 17V for startup), VCS = VCSSC = VDITHER/SYNC = VFB = VFFB = VDCLMP = VGND, VEN = +2V, NDRV = AUXDRV = SS = COMP = unconnected, RRT = 34.8kI, RDT = 25kI, CIN = 1FF, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.
PAGE 7
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Typical Operating Characteristics (VIN = 12V (for MAX5974A/MAX5974C, bring VIN up to 17V for startup), VCS = VCSSC = VDITHER/SYNC = VFB = VFFB = VDCLMP = VGND, VEN = 2V, NDRV = AUXDRV = SS = COMP = unconnected, RRT = 34.8kI, RDT = 25kI, unless otherwise noted.) IN UVLO WAKE-UP LEVEL vs. TEMPERATURE 16.0 15.9 8.4 8.3 8.2 8.1 15.8 8.0 15.7 -15 10 35 60 -15 -40 85 10 35 60 7.2 7.1 7.0 6.9 6.
PAGE 8
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Typical Operating Characteristics (continued) (VIN = 12V (for MAX5974A/MAX5974C, bring VIN up to 17V for startup), VCS = VCSSC = VDITHER/SYNC = VFB = VFFB = VDCLMP = VGND, VEN = 2V, NDRV = AUXDRV = SS = COMP = unconnected, RRT = 34.8kI, RDT = 25kI, unless otherwise noted.) SWITCHING FREQUENCY vs. RRT VALUE 10.03 10.02 10.01 10.00 9.
PAGE 9
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Typical Operating Characteristics (continued) (VIN = 12V (for MAX5974A/MAX5974C, bring VIN up to 17V for startup), VCS = VCSSC = VDITHER/SYNC = VFB = VFFB = VDCLMP = VGND, VEN = 2V, NDRV = AUXDRV = SS = COMP = unconnected, RRT = 34.8kI, RDT = 25kI, unless otherwise noted.
PAGE 10
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Typical Operating Characteristics (continued) (VIN = 12V (for MAX5974A/MAX5974C, bring VIN up to 17V for startup), VCS = VCSSC = VDITHER/SYNC = VFB = VFFB = VDCLMP = VGND, VEN = 2V, NDRV = AUXDRV = SS = COMP = unconnected, RRT = 34.8kI, RDT = 25kI, unless otherwise noted.) TRANSCONDUCTANCE HISTOGRAM (MAX5974A/MAX5974B) 2.6 20 2.5 2.4 MAX5974A/MAX5974B 15 20 N (%) 2.
PAGE 11
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Typical Operating Characteristics (continued) (VIN = 12V (for MAX5974A/MAX5974C, bring VIN up to 17V for startup), VCS = VCSSC = VDITHER/SYNC = VFB = VFFB = VDCLMP = VGND, VEN = 2V, NDRV = AUXDRV = SS = COMP = unconnected, RRT = 34.8kI, RDT = 25kI, unless otherwise noted.
PAGE 12
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Pin Configuration AUXDRV NDRV PGND CS TOP VIEW 12 11 10 9 IN 13 MAX5974A MAX5974B MAX5974C MAX5974D EN 14 DCLMP 15 EP 2 3 4 FFB DT 1 RT + DITHER/ SYNC SS 16 8 CSSC 7 GND 6 FB 5 COMP THIN QFN Pin Description 12 PIN NAME FUNCTION 1 DT Dead-Time Programming Resistor Connection.
PAGE 13
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Pin Description (continued) PIN NAME 6 FB 7 GND Signal Ground 8 CSSC Current Sense with Slope Compensation Input. A resistor connected from CSSC to CS programs the amount of slope compensation. See the Programmable Slope Compensation section. 9 CS Current-Sense Input. Current-sense connection for average current sense and cycle-by-cycle current limit.
PAGE 14
1 3 DT RT SYNC PGND DRIVER 0.5A/-0.3A VC PGND DRIVER 1A/-0.
PAGE 15
Maxim Integrated 1 3 DT RT SYNC PGND DRIVER 0.5A/-0.3A VC PGND DRIVER 1A/-0.
PAGE 16
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Detailed Description The MAX5974A/MAX5974B/MAX5974C/MAX5974D are optimized for controlling a 25W to 50W active-clamped, self-driven synchronous rectification forward converter in continuous-conduction mode. The main switch gate driver (NDRV) and the active-clamped switch driver (AUXDRV) are sized to optimize efficiency for 25W design. The features-rich devices are ideal for PoE IEEE 802.3af/at-powered devices.
PAGE 17
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers UVLO on Power Source The enable input has an accurate threshold of 1.26V (max). For applications that require a UVLO on the power source, connect a resistive divider from the power source to EN to GND as shown in Figure 1. A zener diode between IN and GND is required to prevent the NDRV and AUXDRV gate-drive voltages from exceeding 20V, the maximum allowed gate voltage of power FETs.
PAGE 18
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Because the MAX5974B/MAX5974D are designed for use with low-voltage power sources such as wall adapters outputting 12V to 24V, they have a lower UVLO wake-up threshold of 8.4V. VS RIN Startup Operation The device starts up when the voltage at IN exceeds 16V (MAX5974A/MAX5974C) or 8.4V (MAX5974B/MAX5974D) and the enable input voltage is greater than 1.26V.
PAGE 19
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers n-Channel MOSFET Gate Driver The NDRV output drives an external n-channel MOSFET. NDRV can source/sink in excess of 650mA/1000mA peak current; therefore, select a MOSFET that yields acceptable conduction and switching losses. The external MOSFET used must be able to withstand the maximum clamp voltage.
PAGE 20
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Peak Current Limit The current-sense resistor (RCS in the Typical Application Circuits), connected between the source of the n-channel MOSFET and PGND, sets the current limit. The current-limit comparator has a voltage trip level (VCS-PEAK) of 400mV.
PAGE 21
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers When VCSAVG falls below VFFB, the device folds back the switching frequency to 1/2 the original value to reduce switching losses and increase the converter efficiency.
PAGE 22
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Programmable Slope Compensation The device generates a current ramp at CSSC such that its peak is 50FA at 80% duty cycle of the oscillator. An external resistor connected from CSSC to the CS then converts this current ramp into programmable slopecompensation amplitude, which is added to the currentsense signal for stability of the peak current-mode control loop.
PAGE 23
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Choose a higher value for RIN than the one calculated above if a longer startup time can be tolerated in order to minimize power loss on this resistor. Active Clamp Circuit Traditional clamp circuits prevent transformer saturation by channeling the magnetizing current (IM) of the transformer onto a dissipative RC network.
PAGE 24
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Layout Recommendations During on-time, the coupled output is: N VCOUPLED-ON = −(VS × S N P NC NO − VOUT ) where VS is the input supply voltage.
PAGE 25
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Typical Application Circuits VS 36V TO 57V L1 3.3mH CBULK 33µF D1 NT RIN 100kI D2 L2 6.8µH CIN 1µF 25V D3 RDCLMP1 30.1kI 1% PGOOD NP IN T1 NS RGATE2 10I RGATE1 10I COUT5 COUT1 COUT2 COUT3 COUT4 0.1µF N REN 100kI N2 5i412DP RFB2 2.49kI 1% D4 EN RDCLMP2 750I 1% 5V, 5A RFB1 7.5kI 1% N DCLMP CSS 0.1µF SS N1 5i412DP MAX5974C MAX5974D IN (OPTOCOUPLER FEEDBACK) RDT 16.
PAGE 26
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Typical Application Circuits (continued) D6 RFB1 54.9kI 1% CSNUB RSNUB 10pF 69.8I 1% VS 36V TO 57V CBULK 33µF 63V TO FB RFB2 10kI 1% RIN 100kI CIN 1µF 25V RDCLMP1 30.1kI 1% NP T1 RGATE2 10I D3 NS RGATE1 10I COUT5 0.1µF D4 N DCLMP CSS 0.1µF N1 5i412DP MAX5974A MAX5974B SS (COUPLED INDUCTOR FEEDBACK) DT CDITHER 10nF N2 5i412DP N EN RDT 16.
PAGE 27
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Typical Application Circuits (continued) D1 L1 VS NT CBULK D2 RIN L2 CIN T1 D3 NP NS RGATE2 COUT1 COUT2 COUT3 COUT4 RGATE1 N IN RDCLMP1 REN 100kI N2 RFB1 RFB2 D4 PGOOD N EN RDCLMP2 N1 DCLMP MAX5974C MAX5974D CSS SS RDT DT RDITHER CDITHER CCLAMP RGATE3 DITHER/ SYNC RRT NDRV N N3 RGATE4 P AUXDRV RT N4 CAUX RFFB FFB CS CSSC FB RCSSC COMP Rz GND D5 RAUX PGND RCS CCOMP
PAGE 28
MAX5974A/MAX5974B/MAX5974C/MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers Revision History REVISION NUMBER REVISION DATE 0 6/10 Initial release 1 9/10 Introduced the MAX5974B/MAX5974D. Updated the Absolute Maximum Ratings, Electrical Characteristics, Pin Description, the p-Channel MOSFET Gate Driver, Frequency Foldback for High-Efficiency Light-Load Operation sections, and Typical Application Circuits.