LTC4269-1

Manufacturer Part NumberLTC4269-1
DescriptionIEEE 802.3 At PD And Synchronous No-Opto Flyback Controller
ManufacturerLinear Technology Corporation
LTC4269-1 datasheet
 


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FEATURES
n
25.5W IEEE 802.3at Compliant (Type 2) PD
Integrated State-of-the-Art Synchronous Flyback
n
Controller
– Isolated Power Supply Effi ciency >92%
– 88% Effi ciency Including Diode Bridge and
Hot Swap™ FET
n
Flexible Integrated Auxiliary Power Support
Superior EMI Performance
n
n
Robust 100V 0.7Ω (Typ) Integrated Hot Swap MOSFET
IEEE 802.3at High Power Available Indicator
n
Integrated Signature Resistor and Programmable
n
Class Current
Undervoltage, Overvoltage and Thermal Protection
n
n
Short-Circuit Protection with Auto-Restart
n
Programmable Soft-Start and Switching Frequency
Complementary Power Good Indicators
n
Thermally Enhanced 7mm × 4mm DFN Package
n
APPLICATIONS
n
VoIP Phones with Advanced Display Options
n
Dual-Radio Wireless Access Points
PTZ Security Cameras
n
n
RFID Readers
n
Industrial Controls
TYPICAL APPLICATION
~
+
54V FROM
DATA PAIR
~
~
+
54V FROM
SPARE PAIR
~
0.1μF
DESCRIPTION
The LTC
controller and switching regulator intended for high
power IEEE 802.3at and 802.3af applications. The
LTC4269-1 is targeted for high effi ciency, single and
multioutput applications from 10W to 25W. By support-
ing both 1-event and 2-event classifi cations, as defi ned
by the IEEE, the LTC4269-1 can be used in a wide range
of product confi gurations.
The LTC4269-1 synchronous, current mode, fl yback con-
troller generates multiple supply rails in a single conversion
step providing for the highest system effi ciency while main-
taining tight regulation across all outputs. The LTC4269-1
includes Linear Technology’s patented No-Opto feedback
topology to provide full IEEE 802.3 isolation without the
need of an opto-isolator circuit. A true soft-start function
allows graceful ramp-up of all output voltages.
All Linear Technology PD solutions include a shutdown
pin to provide fl exible auxiliary power options. The
LTC4269-1 can accommodate adaptor voltages from 18V
to 60V and supports both PoE or aux dominance options.
The LTC4269-1 is available in a space saving 32-pin DFN
package.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents, including
5841643.
25W High Effi ciency PD Solution
10μH
V
IN
+
2.2μF
10μF
39k
383k
27.4k
10μF
TO MICRO
14k
3.01k
CONTROLLER
UVLO
T2P
FB
V
PG
CC
V
PORTP
R
CLASS
30.9Ω
LTC4969-1
SHDN
V
PORTN
V
SYNC
GND
OSC
PGDLY
t
ENDLY
R
NEG
ON
CMP
12k
100k
38.3k
1.21k
33pF
LTC4269-1
IEEE 802.3at PD with
Synchronous No-Opto
Flyback Controller
4269-1 is an integrated Powered Device (PD)
®
0.18μH
5V
5A
+
47μF
100μF
+
SENSE
33mΩ
SENSE
SG
2.2nF
V
1μF
CMP
C
CMP
10nF
0.1μF
42691 TA01a
42691f
1

LTC4269-1 Summary of contents

  • Page 1

    ... LTC4269-1 is targeted for high effi ciency, single and multioutput applications from 10W to 25W. By support- ing both 1-event and 2-event classifi cations, as defi ned by the IEEE, the LTC4269-1 can be used in a wide range of product confi gurations. The LTC4269-1 synchronous, current mode, fl yback con- troller generates multiple supply rails in a single conversion step providing for the highest system effi ...

  • Page 2

    ... LTC4269-1 www.DataSheet4U.com ABSOLUTE MAXIMUM RATINGS (Notes 1, 2) Pins with Respect to V PORTN V Voltage ......................................... –0.3V to 100V PORTP V Voltage ......................................... –0. NEG V Pull-Up Current ..................................................1A NEG SHDN ....................................................... –0.3V to 100V R , Voltage ............................................ –0. CLASS R Source Current ...........................................50mA CLASS PWRGD Voltage (Note 3) Low Impedance Source ......V Sink Current .........................................................5mA PWRGD, T2P Voltage ............................... – ...

  • Page 3

    ... Pin Voltage Pulled 57V PORTP PORTN Tested at 0.5mA 52V 48V, Output PORTP NEG Voltage Is with Respect to V NEG Tested at 2mA 0V, Voltage with Respect to V NEG V = 11V 0V, Voltage with Respect to V PWRGD NEG LTC4269-1 MIN TYP MAX 60 l 1.5 9 12.5 l 37 4 ...

  • Page 4

    ... LTC4269-1 www.DataSheet4U.com ELECTRICAL CHARACTERISTICS temperature range, otherwise specifi cations are at T PARAMETER PWM Controller (Note 10) Power Supply V Turn-On Voltage CC(ON) V Turn-Off Voltage CC(OFF) V Hysteresis CC V Shunt Clamp CC V Supply Current ( Start-Up Current CC Feedback Amplifi er Feedback Regulation Voltage (V ...

  • Page 5

    ... CC Note 4: All voltages are with respect to V PORTN Note 5: Input voltage specifi cations are defi ned with respect to LTC4269-1 pins and meet IEEE 802.3af/at specifi cations when the input diode bridge is included. Note 6: Signature resistance is measured via the ΔV/ΔI method with the minimum Δ ...

  • Page 6

    ... VOLTAGE (V) PORTP Signature Resistance vs Input Voltage – V1 RESISTANCE = = I I – DIODES: HD01 T = 25°C A IEEE UPPER LIMIT 26 LTC4269 DIODES 25 24 LTC4269-1 ONLY IEEE LOWER LIMIT VOLTAGE (V) PORTP PWRGD, T2P Output Low Voltage vs Current 0 ...

  • Page 7

    ... G13 Feedback Pin Input Bias vs Temperature 300 R OPEN CMP 250 200 150 100 50 0 125 100 –50 – TEMPERATURE (°C) 42691 G16 LTC4269-1 V Current vs Temperature DYNAMIC CURRENT 1nF , STATIC PART CURRENT 14V 100 125 – ...

  • Page 8

    ... LTC4269 TYPICAL PERFORMANCE CHARACTERISTICS Feedback Amplifi er Output Current 125°C 50 –40° –10 –30 –50 –70 0.9 1 1.1 1.2 1.3 1.4 V (V) FB Feedback Amplifi er Voltage Gain vs Temperature 1700 1650 1600 1550 1500 ...

  • Page 9

    ... TEMPERATURE (° 100 125 42691 G27 R = 27.4k PGDLY R = 16.9k PGDLY 100 125 42691 G29 LTC4269-1 Minimum PG On-Time vs Temperature 340 R = 158k tON(MIN) 330 320 310 300 290 280 270 260 –50 – 100 125 TEMPERATURE (°C) 42691 G28 ...

  • Page 10

    ... LTC4269-1 www.DataSheet4U.com PIN FUNCTIONS SHDN (Pin 1): Shutdown Input. Use this pin for auxiliary power application. Drive SHDN high to disable LTC4269-1 operation and corrupt the signature resistance. If unused, tie SHDN PORTN T2P (Pin 2): Type 2 PSE Indicator, Open-Drain. Low imped- ance indicates the presence of a Type 2 PSE. ...

  • Page 11

    ... Exposed Pad (Pin 33): Ground. This is the negative rail connection for both signal ground and gate driver grounds of the fl yback controller. This pin should be connected NEG LTC4269 set delay from PGDLY (Pins 26, 27): System Negative Rail. Connects V through an internal power MOSFET. Pin 26 and and features a 14V clamp. ...

  • Page 12

    ... LTC4269-1 www.DataSheet4U.com BLOCK DIAGRAM SHDN 1 T2P 2 R CLASS PORTN 5 V PORTN – 15.3V UVLO 18 OSC 15 OSCILLATOR SYNC PGDLY 23 ENDLY CLASSIFICATION CURRENT LOAD + 1.237V 16k – CONTROL CIRCUITS BOLD LINE INDICATES ...

  • Page 13

    ... PD that must operate under the IEEE 802.3at standard. In particular, the LTC4269-1 provides the T2P indicator bit which recognizes 2-event classifi cation. This indicator bit may be used to alert the LTC4269-1 output load that a Type 2 PSE is present. With an internal signature resistor, classifi cation circuitry, inrush control, ...

  • Page 14

    ... The input diode bridge introduces a voltage drop that affects the range for each mode of operation. The LTC4269-1 compensates for these voltage drops so that a PD built with the LTC4269-1 meets the IEEE 802.3af/IEEE 802.3at-established voltage ranges. Note the Electrical Characteristics are referenced with respect to the LTC4269- 1 package pins ...

  • Page 15

    ... The PSE repeats this sequence, signaling the 2nd Clas- sifi cation and 2nd mark event occurrence. This alerts the LTC4269-1 that a Type 2 PSE is present. The Type 2 PSE then applies power to the PD and the LTC4269-1 charges up the reservoir capacitor C1 with a controlled inrush cur- rent ...

  • Page 16

    ... TRACKS V PORTN The LTC4269-1 also maintains a positive I-V slope through- out the classifi cation range up to the on-voltage. In the = 30.9Ω event a PSE overshoots beyond the classifi cation voltage range, the available load current aids in returning the PD back into the classifi ...

  • Page 17

    ... OFF THRESHOLD 30.7V OVLO THRESHOLD 71.0V Figure 5. LTC4269-1 ON/OFF and Overvoltage Lockout Once C1 is fully charged, the LTC4269-1 turns on is internal MOSFET and passes power to the PD load. The LTC4269- 1 continues to power the PD load as long as the input voltage does not fall below the OFF threshold. When the LTC4269-1 input voltage falls below the OFF threshold, the PD load is disconnected, and classifi ...

  • Page 18

    ... OVERVOLTAGE LOCKOUT The LTC4269-1 includes an overvoltage lockout (OVLO) feature (Figure 6) which protects the LTC4269-1 and its load from an overvoltage event. If the input voltage ex- ceeds the OVLO threshold, the LTC4269-1 discontinues PD operation. Normal operations resume when the input voltage falls below the OVLO threshold and when C1 is charged up ...

  • Page 19

    ... Figure 2 shows how two diode bridges are typically con- nected application. One bridge is dedicated to the data pair while the other bridge is dedicated to the spare pair. The LTC4269-1 supports the use of either silicon or Schottky input diode bridges. However, there are tradeoffs in the choice of diode bridges. ...

  • Page 20

    ... LTC4269-1 recognizes this sequence, and provides an indicator bit, declaring the presence of a Type 2 PSE. The open-drain output provides the option to use this signal to communicate to the LTC4269-1 load leave the pin unconnected. Figure 8 shows two interface options using the T2P pin and the opto-isolator ...

  • Page 21

    ... D1. The components surrounding the SHDN pin are selected so that the LTC4269-1 does not disconnect power to the output until the auxiliary supply exceeds 36V. This confi guration is an auxiliary-dominant confi guration. ...

  • Page 22

    ... This precludes the need of an opto-isolator in isolated designs, thus greatly improving dynamic response and reliability. The LTC4269-1 has a unique feedback amplifi er that samples a transformer winding voltage during the fl yback period and uses that voltage to control output voltage. ...

  • Page 23

    ... VOLTAGE PG VOLTAGE SG VOLTAGE V FLBK LTC4269-1 FEEDBACK AMP – V CMP 1.237V 42691 F10a Figure 10a. LTC4269-1 Switching Regulator Feedback Amplifi ON(MIN) ENABLE DELAY Figure 10b. LTC4269-1 Switching Regulator Timing Diagram LTC4269-1 T1 FLYBACK • • VCMP PRIMARY ...

  • Page 24

    ... V node slew rate. CMP 24 Load Compensation Theory The LTC4269-1 uses the flyback pulse to obtain information about the isolated output voltage. An error source is caused by transformer secondary current fl ow through the synchronous MOSFET R nonzero impedances of the transformer secondary and output capacitor. This was represented previously by the ...

  • Page 25

    ... Transformer design/specifi cation is the most critical part of Δ • • successful application of the LTC4269-1. The following SF OUT sections provide basic information about designing the transformer and potential tradeoffs. If you need help, the LTC Applications group is available to assist in the choice • ...

  • Page 26

    ... MOSFET R cross regulation. The feedback winding usually provides both the feedback voltage and power for the LTC4269-1. Set the turns ratio between the output and feedback winding to provide a rectifi ed voltage that under worst-case conditions is greater than the 11V maximum V turn-off voltage ...

  • Page 27

    ... The main design goals for core selection are reducing copper losses and preventing saturation. Ferrite core material saturates hard, rapidly reducing inductance when the peak design current is exceeded. This results LTC4269 ...

  • Page 28

    ... LTC4269-1 www.DataSheet4U.com APPLICATIONS INFORMATION in an abrupt increase in inductor ripple current and, consequently, output voltage ripple. Do not allow the core to saturate! The maximum peak primary current occurs at minimum ⎛ MIN = + I • 1 ⎝ ⎜ • MIN ( ) MAX now : ...

  • Page 29

    ... R in place and R load compensation (from step 2). Setting Frequency The switching frequency of the LTC4269-1 is set by an external capacitor connected between the OSC pin and ground. Recommended values are between 200pF and 33pF , yielding switching frequencies between 50kHz and 250kHz. Figure 12 shows the nominal relationship between to V times effi ...

  • Page 30

    ... ON(MIN) Even though the LTC4269-1 has a robust gate drive, the gate transition time slows with very large MOSFETs. Increase delay time as required when using such MOSFETs. The enable delay resistor is set with the following ...

  • Page 31

    ... PGDLY good starting point is 15k. Soft-Start Function The LTC4269-1 contains an optional soft-start function that is enabled by connecting an external capacitor between the SFST pin and ground. Internal circuitry prevents the control voltage at the V pin from exceeding that on the SFST CMP pin. There is an initial pull-up circuit to quickly bring the SFST voltage to approximately 0.8V. From there it charges to approximately 2.8V with a 20μ ...

  • Page 32

    ... undersized before stabilization and the LTC4269-1 turns off. The V node then begins to charge back up via R k threshold, where the part again turns on. Depending upon the circuit, this may result in either several on-off cycles before proper operation is reached, or permanent relaxation 18 7 ...

  • Page 33

    ... Figure 15. V Compensation Network CMP In further contrast to traditional current mode switchers, V pin ripple is generally not an issue with the LTC4269-1. CMP The dynamic nature of the clamped feedback amplifi er forms an effective track/hold type response, whereby the V voltage changes during the fl yback pulse, but is then ...

  • Page 34

    ... So, divide the load current by (1 – DC). If the output load current is relatively constant, the feedback resistive divider is used to compensate for these losses. Otherwise, use the LTC4269-1 load compensation circuitry ( ) + • ...

  • Page 35

    ... The parasitic inductance creates an LC tank with the . The Miller capacitance MOSFET gate capacitance. In less than ideal layouts, a series resistance of 5Ω or more may help to dampen the to DS ringing at the expense of slightly slower rise and fall times LTC4269-1 determined, calculate the primary-side power MILLER ( ) δ ...

  • Page 36

    ... LTC4269-1 www.DataSheet4U.com APPLICATIONS INFORMATION and poorer effi ciency. The LTC4269-1 gate drives will clamp the max gate voltage to roughly 7.5V, so you can safely use MOSFETs with maximum V of 10V and larger. GS Synchronous Gate Drive There are several different ways to drive the synchronous gate MOSFET ...

  • Page 37

    ... Refer to the PC Board Layout section for more details. ELECTRO STATIC DISCHARGE AND SURGE PROTECTION The LTC4269-1 is specifi operate with an absolute maximum voltage of –100V and is designed to tolerate brief overvoltage events. However, the pins that interface to the outside world (primarily V ) can routinely see peak voltages in excess of 10kV ...

  • Page 38

    ... For applications with multiple switching power converters connected to the same input supply, make sure that the input fi lter capacitor for the LTC4269-1 is not shared with other converters. AC input current from another converter could cause substantial input voltage ripple which could interfere with the LTC4269-1 operation. A few inches of PC trace or wire (L ≅ ...

  • Page 39

    ... TYPICAL APPLICATIONS LTC4269-1 42691f 39 ...

  • Page 40

    ... OUTPUT CURRENT (A) 40 PoE-Based 5V, 5A Power Supply 10μH + 2.2μF 10μF 36V BAS21 PDZ36B 27.4k 383k BSS63LT1 20Ω 14.0k 3.01k UVLO FB V PORTP SHDN R CLASS LTC4269-1 30.9Ω 24k V PORTN V SYNC GND OSC PGDLY t ENDLY NEG ON 33pF 100k 12k 3.0 3.5 4.0 4.5 5.0 42691 TA03b T1 • • • 39k 150Ω ...

  • Page 41

    ... SHDN R CLASS LTC4269-1 30.9Ω 24k V PORTN V SYNC GND OSC PGDLY t ENDLY NEG ON 33pF 100k 12k 38.3k IN 1.4 1.6 1.8 2.0 42691 TA04b LTC4269-1 T1 • 0.33μH 10μF • • 20k 150Ω 47pF + 1μF 22μF 15Ω FDS3572 470pF FDS2582 2.2nF V PG 2kV CC + SENSE 33mΩ – SENSE ...

  • Page 42

    ... LOAD CURRENT (A) 42 PoE-Based 3.3V, 7A Power Supply 10μH + 2.2μF 10μF 36V BAS21 PDZ36B 29.4k 383k BSS63LT1 20Ω 14.0k 3.01k UVLO FB V PORTP SHDN R CLASS LTC4269-1 30.9Ω 24k V PORTN V SYNC GND OSC PGDLY t ENDLY NEG ON 33pF 100k 12k 38.3k 37V IN 4.9 5.6 6.3 7.0 42691 TA05b 0.18μH T1 • 47μF • ...

  • Page 43

    ... DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE LTC4269 0.115 TYP 17 TYP 6.43 ±0.10 2.65 ± ...

  • Page 44

    ... LTC4269-1 www.DataSheet4U.com RELATED PARTS PART NUMBER DESCRIPTION LT ® 1952 Single Switch Synchronous Forward Counter LTC3803-3 Current Mode Flyback DC/DC Controller in ThinSOT LTC3805 Adjustable Frequency Current Mode Flyback Controller LTC3825 Isolated No-Opto Synchronous Flyback Controller with Wide Input Supply Range LTC4257-1 IEEE 802.3af PD Interface Controller LTC4258 Quad IEEE 802 ...