MAX5942BCSE Maxim Integrated, MAX5942BCSE Datasheet

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MAX5942BCSE

Manufacturer Part Number
MAX5942BCSE
Description
Power Switch ICs - POE / LAN
Manufacturer
Maxim Integrated
Datasheet

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The MAX5942A/MAX5942B integrate a complete power
IC for powered devices (PD) in a power-over-ethernet
(PoE) system. The MAX5942A/MAX5942B provide a PD
interface and a compact DC-DC PWM controller suitable
for flyback and forward converters in either isolated or
nonisolated designs.
The MAX5942A/MAX5942B PD interface complies with
the IEEE™ 802.3af standard, providing the PD with a
detection signature, a classification signature, and an
integrated isolation switch with programmable inrush cur-
rent control. These devices also feature power-mode
undervoltage lockout (UVLO) with wide hysteresis and
power-good status outputs.
The MAX5942A/MAX5942B also integrate all the build-
ing blocks necessary for implementing DC-DC fixed-
frequency isolated power supplies. This device is a
current-mode controller with an integrated high startup
circuit suitable for isolated telecom/industrial voltage
range power supplies. A high-voltage startup circuit
allows the PWM controller to draw power directly from the
18V to 67V input supply during startup. The switching
frequency is internally trimmed to 275kHz ±10%, thus
reducing magnetics and filter components. The
MAX5942A allows an 85% operating duty cycle and can
be used to implement flyback converters. The MAX5942B
limits the operating duty cycle to less than 50% and can
be used in single-ended forward converters. The
MAX5942A/MAX5942B are designed to work with or with-
out an external diode bridge in front of the PD.
The MAX5942A/MAX5942B are available in 16-pin SO
packages.
19-3024; Rev 2; 9/04
Typical Operating Circuit appears at end of data sheet.
IEEE is a trademark of the Institute of Electrical and Electronics
Engineers.
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim's website at www.maxim-ic.com.
IP Phones
Wireless Access Nodes
Internet Appliances
Computer Telephony
Security Cameras
Power Devices in Power-Over-Ethernet/
Power-Over-MDI
Interface/PWM Controller for Power Devices
________________________________________________________________ Maxim Integrated Products
General Description
IEEE 802.3af Power-Over-Ethernet
Applications
♦ Powered Device Interface
♦ PWM Controller
*Future product—contact factory for availability.
MAX5942AESE*
MAX5942ACSE
MAX5942BESE*
MAX5942BCSE
Power Supply
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 FET
Programmable Inrush Current Control/ULVO
PGOOD/PGOOD Outputs Enable PWM
Controller
Wide Input Range: 18V to 67V
Isolated (Without Optocoupler) or Nonisolated
Current-Mode Control
Leading-Edge Blanking
Internally Trimmed 275kHz ±10% Oscillator
Soft-Start
PART
TOP VIEW
SS_SHDN
ULVO
GATE
V
RCL
V
V+
DD
FB
EE
-40°C to +85°C
-40°C to +85°C
TEMP RANGE
0°C to +70°C
0°C to +70°C
1
2
6
3
4
5
7
8
Ordering Information
MAX5942A
MAX5942B
SO
Pin Configuration
PIN-
PACKAGE
16 SO
16 SO
16 SO
16 SO
16
15
14
13
12
11
10
9
V
NDRV
V-
CS
GND
PGOOD
PGOOD
OUT
CC
Features
M A X D U T Y
C YC L E ( % )
85
85
50
50
1

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MAX5942BCSE Summary of contents

Page 1

... Power Supply Current-Mode Control Leading-Edge Blanking Internally Trimmed 275kHz ±10% Oscillator Soft-Start PART MAX5942AESE* MAX5942ACSE MAX5942BESE* Applications MAX5942BCSE *Future product—contact factory for availability. TOP VIEW Features Ordering Information PIN TEMP RANGE PACKAGE -40°C to +85° 0° ...

Page 2

IEEE 802.3af Power-Over-Ethernet Interface/PWM Controller for Power Devices ABSOLUTE MAXIMUM RATINGS (All voltages are referenced unless otherwise noted.) EE GND........................................................................-0.3V to +90V OUT, PGOOD ...........................................-0.3V to (GND + 0.3V) RCL, GATE .............................................................-0.3V to +12V UVLO ........................................................................-0.3V to ...

Page 3

Interface/PWM Controller for Power Devices ELECTRICAL CHARACTERISTICS (continued 48V, GATE = PGOOD = PGOOD = OPEN, V- tied to OUT, V+ tied to GND, UVLO = (GND - unless otherwise noted. Typical ...

Page 4

IEEE 802.3af Power-Over-Ethernet Interface/PWM Controller for Power Devices ELECTRICAL CHARACTERISTICS (PWM Controller) (continued) (All voltages referenced to V 13V, a 10µF capacitor connects V DD SS_SHDN, NDRV = open circuit 3V PARAMETER SYMBOL I ...

Page 5

Interface/PWM Controller for Power Devices ELECTRICAL CHARACTERISTICS (PWM Controller) (continued) (All voltages referenced to V 13V, a 10µF capacitor connects V DD SS_SHDN, NDRV = open circuit 3V PARAMETER SYMBOL SOFT-START SS Source Current ...

Page 6

IEEE 802.3af Power-Over-Ethernet Interface/PWM Controller for Power Devices (V = (GND - 48V, GATE = PGOOD = PGOOD = OUT = OPEN, UVLO = Typical values are +25°C. All voltages are ...

Page 7

Interface/PWM Controller for Power Devices (V = (GND - 48V, GATE = PGOOD = PGOOD = OUT = OPEN, UVLO = Typical values are +25°C. All voltages are referenced to V ...

Page 8

IEEE 802.3af Power-Over-Ethernet Interface/PWM Controller for Power Devices (V = (GND - 48V, GATE = PGOOD = PGOOD = OUT = OPEN, UVLO = Typical values are +25°C. All voltages are ...

Page 9

Interface/PWM Controller for Power Devices (V = (GND - 48V, GATE = PGOOD = PGOOD = OUT = OPEN, UVLO = Typical values are +25°C. All voltages are referenced to V ...

Page 10

... V EE OUT impedance. 12 GND Ground. Referenced to V Current-Sense Input. Referenced to V-. Turns power switch off if V current limiting also the feedback for the current-mode controller. CS connects to the PWM controller 13 CS through a leading-edge blanking circuit Ground the ground terminal of the PWM controller. ...

Page 11

Interface/PWM Controller for Power Devices Table 1. PD Power Classification/R CLASS USAGE 0 Default 1 Optional 2 Optional 3 Optional 4 Not allowed *Class 4 reserved for future use. Detailed Description The MAX5942A/MAX5942B integrate a complete power IC for powered ...

Page 12

IEEE 802.3af Power-Over-Ethernet Interface/PWM Controller for Power Devices Table 2. Setting Classification Current CLASS R (Ω ( 10k 12 732 12 392 12 255 12.6 to ...

Page 13

Interface/PWM Controller for Power Devices The PSE determines the class applying a volt- age at the PD input and measures the current sourced out of the PSE. When the PSE applies a voltage between 12.6V and ...

Page 14

IEEE 802.3af Power-Over-Ethernet Interface/PWM Controller for Power Devices Thermal Dissipation During classification mode, if the PSE applies the maxi- mum DC voltage, the maximum voltage drop from GND to V will be 13V. If the maximum classification cur- RCL rent ...

Page 15

Interface/PWM Controller for Power Devices HIGH- VOLTAGE V- REGULATOR EN MAX5942A ONLY COMPENSATION 26mV/µs 26mV/µs 1MΩ 50kΩ FB ERROR AMP SS_SHDN 2.4V 0.25V Figure 4. MAX5942A/MAX5942B PWM Controller Functional Diagram ______________________________________________________________________________________ IEEE 802.3af Power-Over-Ethernet IN BIAS ...

Page 16

IEEE 802.3af Power-Over-Ethernet Interface/PWM Controller for Power Devices V IN (36V TO 72V 4.7µF C 25.5kΩ 10µ 0.1µF Figure 5. Forward Converter Current-Sense Comparator The current-sense (CS) comparator and its associated logic limit ...

Page 17

Interface/PWM Controller for Power Devices 25.5kΩ Figure 6. Flyback Converter 25.5kΩ Figure 7. Flyback Converter ______________________________________________________________________________________ IEEE 802.3af Power-Over-Ethernet N V+ GND V DD ...

Page 18

IEEE 802.3af Power-Over-Ethernet Interface/PWM Controller for Power Devices PWM Comparator and Slope Compensation An internal 275kHz oscillator determines the switching frequency of the controller. At the beginning of each cycle, NDRV switches the N-channel MOSFET on. NDRV switches the external ...

Page 19

Interface/PWM Controller for Power Devices V = Output voltage (5V). OUT V = Voltage drop across D1 (typically 0.5V for D1 power Schottky diodes Minimum value of maximum operating duty MAX cycle (44%). V = Minimum input voltage ...

Page 20

IEEE 802.3af Power-Over-Ethernet Interface/PWM Controller for Power Devices Table 3. Component Suppliers COMPONENT Power FETS Current-Sense Resistors Diodes Capacitors Magnetics 6) Choose R according to the following equation: SENSE V ILIM R ≤ SENSE N S × ...

Page 21

Interface/PWM Controller for Power Devices RJ- POWER-OVER SPARE PAIRS GND **R1 SMBJ58CA R = DISC 25.5kΩ 68nF 60V **R2 -48V * OPTIONAL AND R2 ARE OPTIONAL AND WHEN USED, THEY ...

Page 22

IEEE 802.3af Power-Over-Ethernet Interface/PWM Controller for Power Devices POWER-SUPPLY CIRCUIT 1 GND ** DISC 25.5kΩ 68nF 60V ** -48V POWER-SUPPLY CIRCUIT 2 *OPTIONAL. **R1 AND R2 ARE OPTIONAL AND WHEN USED, THEY MUST TOTAL TO 25.5kΩ ...

Page 23

IEEE 802.3af Power-Over-Ethernet Interface/PWM Controller for Power Devices GND R = DISC 25.5kΩ 60V -48V ______________________________________________________________________________________ V+ GND NDRV MAX5942 SS_SHDN PGOOD UVLO RCL PGOOD GATE FB V OUT EE C GATE TRANSISTOR COUNT: ...

Page 24

... Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 24 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2004 Maxim Integrated Products H ...

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