ltc4267-3 Linear Technology Corporation, ltc4267-3 Datasheet
ltc4267-3
Related parts for ltc4267-3
ltc4267-3 Summary of contents
Page 1
... The LTC4267-3 includes an onboard er- ror amplifi er and voltage reference allowing use in both isolated and nonisolated confi gurations. The LTC4267-3 is available in a space saving, low profi le 16-pin SSOP or DFN packages. Class 2 PD with 3.3V Isolated Power Supply ...
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... LTC4267 ABSOLUTE AXI U RATI GS V with Respect to V Voltage ... 0.3V to –100V PORTN PORTP , SIGDISA, PWRGD P OUT Voltage ..................... V + 100V to V PORTN P to PGND Voltage (Note 2) VCC Low Impedance Source ........................... –0. Current Fed .......................................... 5mA into P R Voltage ................. CLASS PORTN PWRGD Current .....................................................10mA R Current ...
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... Sinking 5µA, P – (Note 12) VCC GND TH I /RUN Sourcing 5µA, P – (Note 12) VCC GND 0V, Power MOSFET Off 57V (Note 13) PORTN OUT LTC4267-3 MIN TYP MAX ● –57 ● –1.5 –9.5 ● –12.5 –21 ● –34.8 –36 –37.2 ● –29.3 – ...
Page 4
... The LTC4267-3 is also protected against thermal damage from incorrect classifi cation probing by the PSE. If the LTC4267-3 exceeds the overtemperature threshold, the classifi cation load current is disabled. Note 15: The PD interface includes dual level input current limit. At turn- ...
Page 5
... V VOLTAGE (V) PORTN Signature Resistance vs Input Voltage 28 ∆V V2 – V1 RESISTANCE = = ∆I I – DIODES: S1B T = 25°C A IEEE UPPER LIMIT 26 LTC4267 DIODES 25 24 LTC4267-3 ONLY IEEE LOWER LIMIT 23 22 –60 V1: –1 –3 –7 –5 V2: –2 –4 –6 –8 V VOLTAGE (V) PORTN P Leakage Current ...
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... LTC4267 TYPICAL PERFOR A CE CHARACTERISTICS Reference Voltage vs Temperature 812 VCC 808 804 800 796 792 788 –50 –30 – TEMPERATURE (°C) 42673 G10 Oscillator Frequency vs Supply Voltage 330 320 310 300 290 280 270 6 7 7.5 8 8.5 6.5 V SUPPLY VOLTAGE (V) ...
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... TEMPERATURE (°C) 50 110 70 90 42673 G20 LTC4267-3 I /RUN Start-Up Current Source TH vs Temperature 600 0.1V VCC TURNON ITH/RUN 500 400 300 200 100 0 90 110 –50 – ...
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... PWRGD is referenced to V SIGDISA (Pin 12): Signature Disable Input. SIGDISA al- lows the PD to present an invalid signature resistance and remain inactive. Connecting SIGDISA to V the signature resistance to an invalid value and disables all functions of the LTC4267-3. If unused, tie SIGDISA PORTN V (Pin 13): Positive Power Input. Tie to the input PORTP port power return through the input diodes ...
Page 9
... PD to consume up to 12.95W if an IEEE 802.3af PSE is present. This low level current limit also allows the LTC4267-3 to charge arbitrarily large load capacitors without exceeding the inrush limits of the IEEE 802.3af specifi cation. This dual level current limit provides the system designer with fl ...
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... Power Applied to Switching Regulator *V UVLO includes hysteresis. PORTN Rising input threshold ≅ – 36.0V Falling input threshold ≅ –30.5V **Measured at LTC4267-3 pin. The LTC4267-3 meets the IEEE 802.3af 10V minimum when operating with the required diode bridges pin and must PORTN ...
Page 11
... PD. The LTC4267-3 compensates for the two series diodes in the signature path by offsetting the resistance so that a PD built using the LTC4267-3 will meet the IEEE specifi cation. In some applications it is necessary to control whether or not the PD is detected ...
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... The IEEE 802.3af specifi cation limits the classifi cation time to 75ms because a signifi cant amount of power is dissipated in the PD. The LTC4267-3 is designed to handle the power dissipation for this time period. If the PSE prob- ing exceeds 75ms, the LTC4267-3 may overheat. In this situation, the thermal protection circuit will engage and disable the classifi ...
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... The LTC4267-3 has been specifi cally designed to interface with legacy PSEs which do not meet the inrush current requirement of the IEEE 802.3af specifi cation. At turn-on the LTC4267-3 current limit is set to the lower level. After C1 is charged up and the P – V OUT ...
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... PSE current limit should provide the overall limit for the circuit. For slower rising inputs, the 375mA current limit in the LTC4267-3 will set the charge rate of the capacitor C1. In either case, the PWRGD signal may go inactive briefl y while the capacitor is charged up to the new line voltage ...
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... The PD is designed to operate at a high ambient tem- perature and with the maximum allowable supply (57V). However, there is a limit to the size of the load capacitor that can be charged up before the LTC4267-3 reaches the overtemperature trip point. Hitting the overtemperature trip point intermittently does not harm the LTC4267-3, but it will delay the completion of capacitor charging. Capacitors up to 200µ ...
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... PGND) TURNOFF before the undervoltage lockout disables the switching regulator. This wide UVLO hysteresis range supports applications where a bias winding on the fl yback trans- former is used to increase the effi ciency of the LTC4267-3 switching regulator. The I /RUN can be driven below V TH ...
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... Figure 9. PD Front End with Isolation Transformer, Diode Bridges and Capacitor W U affect the transition point between modes. When using the LTC4267- necessary to pay close attention to this forward voltage drop. Selection of oversized diodes will help keep the PD thresholds from exceeding IEEE specifi cations. ...
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... In order to maintain loop stability, the layout should minimize capacitance at the R ) can be disabled by fl oating the R should not be shorted to V LTC4267-3 classifi cation circuit to attempt to source very large currents and quickly go into thermal shutdown. C11 0.1µF D6 100V ...
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... The IEEE 802.3af specifi cation requires that the PD main- tain a minimum load capacitance of 5µF (provided Figure 11 permissible to have a much larger load capacitor and the LTC4267-3 can charge very large load capacitors before thermal issues become a problem. The load capacitor must be large enough to provide suffi cient energy for proper operation of the switching regulator ...
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... Commercially available error amplifi ers or programmable shunt regulators may include an internal reference of 1.25V or 2.5V. Since the LTC4267-3 internal reference and error amplifi er are not used in an isolated design, tie the V pin to PGND. ...
Page 21
... This stabilizes the control loop against subharmonic oscillation. The amount of reduction in the current comparator threshold (∆V can be calculated using the following equation: ∆V SENSE Note: The LTC4267-3 enforces 6% < Duty Cycle < 80%. Designs not needing slope compensation may replace can be determined R with a short-circuit. SL LTC4267-3 /RUN approaches 1 ...
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... R3 START P VCC 0.1µF NGATE V PORTP 100V R CLASS SENSE R CLASS LTC4267-3 SIGDISA V PORTN /RUN TH P PGND OUT C C Figure 11. Typical LTC4267-3 Application Circuits D1 T1 • OUT PRI SEC • LIM R SENSE PGND V PORTP OPTOISOLATOR ERROR AMPLIFIER ...
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... P threshold. Also, the third winding’s nominal output voltage should be at least 0.5V below the minimum rated P clamp voltage to avoid running up against the LTC4267-3 shunt regulator, needlessly wasting power. P Shunt Regulator ...
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... After some time, the output voltage approaches START the desired value. By this time, the pass transistor Q1 catches the declining voltage on the P virtually all the supply current required by the LTC4267-3 switching regulator START handle the switching current needed to drive NGATE while C maintaining minimum switching voltage. ...
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... MOSFETs specifi cally for Power- over-Ethernet applications. The NGATE pin of the LTC4267-3 drives the gate of the N-channel MOSFET. NGATE will traverse a rail-to-rail volt- age from PGND The designer must ensure the VCC MOSFET provides a low “ ...
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... OPTION 1: AUXILIARY POWER INSERTED BEFORE LTC4267-3 PD RJ45 + – – SPARE – SPARE 8 ISOLATED WALL TRANSFORMER OPTION 2: AUXILIARY POWER INSERTED AFTER LTC4267-3 PD WITH SIGNATURE DISABLED RJ45 + – – SPARE – SPARE 8 ISOLATED WALL TRANSFORMER ...
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... Overlooking this consideration may result in slow power supply ramp up, power-up oscilla- tion, and possibly thermal shutdown. The LTC4267-3 includes a power good signal in the PD interface that can be used to indicate to the switching regulator that the load capacitor is fully charged and ready to handle the switcher load ...
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... In essence, a tight overall layout of the high current loop and careful attention to current density will ensure suc- must be given SENSE cessful operation of the LTC4267 PD. The PD interface section of the LTC4267-3 is relatively im- mune to layout problems. Excessive parasitic capacitance on the R CLASS adjacent to the V tive or capacitive may inadvertently disable the signature resistance. To ensure consistent behavior, the SIGDISA pin should be electrically connected and not left fl ...
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... VCC LTC4267-3 SMAJ58A NGATE 0.1µF PWRGD R SENSE CLASS 45.3Ω SIGDISA I /RUN TH 22nF V PORTN P PGND 27k OUT LTC4267-3 COILTRONICS CTX-02-15242 220k UPS840 300µF* • 9.1V • 1µF 150pF FDC2512 200V 10k 220Ω 0.04Ω 1% 42.2k 1% 42673 TA02 8.06k 1% 5V 1.8A 42673f ...
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... LTC4267-3 U TYPICAL APPLICATIO S 30 42673f ...
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... TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE LTC4267 0.115 TYP 0.20 TYP 3.00 ±0.10 (2 SIDES) 1.65 ± ...
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... McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● 4.7µH 12µF 2.2µF 100V 100V 220k 220k MMTBA42 9.1V MMSD4148 BAS516 PORTP VCC 4.7µF LTC4267-3 SMAJ58A NGATE 10k SENSE R I /RUN CLASS TH P VCC 45.3Ω 100k 1% SIGDISA PWRGD 10k V V PORTN ...