MAX5974A_11 Datasheet, PDF (1/27 Pages) Maxim Integrated Products – Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers

19-5331; Rev 2; 6/11
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Active-Clamped, Spread-Spectrum,
Current-Mode PWM Controllers
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 supply
efficiency. The AUX driver recycles magnetizing cur-
rent 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 fre-
quency (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 volt-
age during transient conditions independent of the line
voltage, allowing the use of a power MOSFET with lower
breakdown voltage. The programmable frequency dither-
ing feature provides low-EMI, spread-spectrum operation.
The MAX5974_ are available in 16-pin TQFN-EP pack-
ages 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
Ordering Information/Selector Guide
PART
MAX5974AETE+
MAX5974BETE+
MAX5974CETE+
MAX5974DETE+
TOP MARK
+AHY
+AHZ
+AIA
+AIB
PIN-PACKAGE
16 TQFN-EP*
16 TQFN-EP*
16 TQFN-EP*
16 TQFN-EP*
UVLO THRESHOLD (V)
16
8.4
16
8.4
Note: All devices are specified over the -40°C to +85°C operating temperature range.
+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.
FEEDBACK MODE
Sample/Hold
Sample/Hold
Continuously Connected
Continuously Connected
________________________________________________________________ Maxim Integrated Products   1
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or visit Maxim’s website at www.maxim-ic.com.