AN296 Silicon_Laboratories, AN296 Datasheet
AN296
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AN296 Summary of contents
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... SIGNAL PAIR SPARE PAIR POWERED DEVICE (PD SPARE PAIR SIGNAL PAIR SIGNAL PAIR SPARE PAIR Copyright © 2007 by Silicon Laboratories AN296 DC/DC Converter TX RX DC/DC Converter TX AN296 ...
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... AN296 The Power Sourcing Equipment (PSE) supplies VDC and must be isolated from earth ground. The powered device (PD) must not consume more than 12.95 W, which translates to no more than 350 mA of steady state input current, allowing for 20 Ω of cabling resistance between the PSE and PD. This means that with practical ...
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... S1B S1B 1000p 1000p 1000p 1000p C10 C10 D11 D11 2 1 D15 D15 S1B S1B Rev. 0.8 AN296 C17 C17 2 1 S1B S1B C16 C16 2 1 S1B S1B C15 C15 2 1 S1B S1B C14 C14 2 1 S1B S1B ...
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... AN296 C6 100u C6 100u DFLT15A DFLT15A 1N4148W 1N4148W 12uF 12uF 100 100 R12 R12 220n 220n C21 C21 100n 100n C22 C22 1u 1u C23 C23 FB PLOSSb 20 5 25.5K 25.5K VSS2 RDET ...
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... During the classification phase, the PSE applies a voltage between 15.5 and 20.5 V, current-limited to 100 mA, and determines the maximum output power requirement. Class Switcher must turn on Switcher must turn off Apply Power Classification Figure 5. Full Power Cycle Power Level that the PSE Must Support 15 15.4 W Reserved (Treat as Class 0) Rev. 0.8 AN296 Time Turn off 5 ...
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... AN296 Over the range of 14.5 to 20.5 V, the PD current during the classification stage must be as shown in Table 1. Table 1. Classification Stage PD Current Class The classification current for the Si3400/01 is set by the resistor, Rclass (R3 in Figures 3 and 4). 3.3. Powerup During detection and classification, the PD must isolate the switcher input filter and not apply power to the load. ...
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... Additionally, the Si3400/01 has an early power loss feature where the voltage on the cable side of the diode bridge is sensed. If this voltage drops to between 25 and 30 V, the power loss signal (PLOSS) is asserted. This allows for early detection of power removal while the switcher input capacitor is still charged. Rev. 0.8 AN296 7 ...
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... AN296 3.6. Signature Resistors and Capacitors and Component Selection Criteria The Si3400/01 is designed to meet 802.3af signature requirements with RDET (connected to pin RDET) = 25.5 kΩ, ±1%. Recommended resistor values for RCLASS (connected to pin RCL) are listed in Table 2. Table 2. RCLASS Recommended Resistor Values Class ...
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... The ripple current that has to be supported in the output filter is × – out out --------------------------------------------------------------- I = ripple ( ( ) × × Vin- Vout D/f (1- D)/f Iripple Figure 7. Voltage Polarity ( ) out f is the forward drop of the diode (D1 in Figure 3), and Rev. 0.8 AN296 t Vout+Vf Iout varies with the in 9 ...
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... AN296 Where L is the inductance µH, Vout = 3 the internally-set switch frequency of approximately 350 kHz 321 mA ripple This is the ripple current into the output filter. The peak-to-peak ripple current that must be handled by the input filter is equal to the average current delivered to the output plus half of the ripple current in the inductor. ...
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... In the continuous mode, current always flows in either the transformer primary or secondary. In the discontinuous mode, the secondary current drops to zero before the next cycle of primary current. Typical waveforms are shown in Figure 9. 500 1000 2000 5000 phase(Gain) in ° Figure 8. Typical Bode Plot Rev. 0.8 AN296 ° 150 100 50 0 -50 -100 -150 -200 ...
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... AN296 N*(Vo+Vf Ipr Isw Isnuber A transformer with a turns ratio of N:1 is used to help reduce peak currents. In the discontinuous mode, the output power, I transformer with some margin for switching losses. If ε is the margin for switching losses (typically 90%), then × × × × ...
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... The FET maximum drain voltage and the maximum voltage at Vpos is about 55 V; so, the snubber must clamp Zener diode and fast recovery diode are recommended to clamp the output at less than 25 V above gives the following ⎞ × ---------------------- - N + ⎠ the peak transformer current is 1. Rev. 0.8 AN296 . POS 13 ...
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... AN296 Increasing the turns ratio will increase snubber power. Therefore, there is an optimal turns ratio that compromises between high peak current at a low turns ratio and high snubber power at a high turns ratio. Silicon Laboratories, Inc. has partnered with Coilcraft to develop flyback transformers that are optimized for maximum efficiency of the Si3400/01 at 3.3, 5, and 12 V output. Recommended part numbers are FA2924-AL for 3.3 V (40 µ ...
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... Figure 11. 2.5 W Load Load Note: Upper trace is output voltage at 500 mV/div (5 V nominal) and lower trace is input current at 100 mA/div. Figure 12 Load to 2.5 W Load 2000 5000 10000 20000 phase(Gain) in ° Rev. 0.8 AN296 ° 150 100 50 0 -50 -100 -150 -200 ...
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... AN296 Note: Input current at 50 mA/div and output voltage at 1 V/div. Figure 13. Isolated Mode Startup with 5 W Load 5. Surge The Si3400/01 has an input clamp that will protect it against surges as spelled out in IEEE 802.3af. IEEE 802.3af specifies a 1000 V surge with 0.3 µsec rise time and 50 µsec fall time applied to each conductor through a series resistance of 402 Ω ...
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... It is also possible to use a lower-voltage auxiliary power source, such diode OR at the output of the switching converter, as shown in Figure 15. Vposs Si3400/01 Diode Surge limiting resistor >100V Vposf CT1 CT2 Si3400/01 SP1 SP2 Vneg Figure 14 Auxiliary Supply Aux Power 12 VDC + Optional 4.7 k 12V + Isolated or Non-Isolated power train Vss Figure 15 Auxiliary Supply Rev. 0.8 AN296 _ Post - Regulator 17 ...
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... AN296 This option may be preferable when a post regulator is required for generation of very low voltages, such as 1 when the post regulator is required for low noise. With the post regulator option, the larger output voltage will again supply the power. In this case, the Si3400/01 will attempt to go through the detection and classification cycle, but if the AUX supply is providing the power, the Si3400/01 will not draw enough dc current, and the PSE may disconnect and cycle continuously ...
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... FET turn on in the case of the primary side snubber. 2 plane on an inner layer. carry up to 325 mA dc. 12 mil traces have been found to be adequate. POSF Rev. 0.8 AN296 2 bottom plane 19 ...
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... AN296 The loops carrying high ac current are as follows: The loop from the input filter, C1–C4, to the transformer retuning from the transformer to SWO, then to V back to the input filter capacitors. The loop from the transformer secondary to D3, the filter capacitor C6, and returning to the transformer secondary ...
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... Si3400/01. The spreadsheets should be used in conjunction with this application note, and additional documentation is included within the spreadsheet. The evaluation boards and reference designs are documented separately and include example layouts and BOM lists Frequency (MHz) Rev. 0.8 AN296 ...
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... AN296 OCUMENT HANGE IST Revision 0.1 to Revision 0.2 Updated schematics and BOM with optimized values for Rev C, Si3400 Updated performance information with measured results for Rev C Si3400 Added new section, "6. Use with an Auxiliary Power Supply" on page 17. Revision 0.2 to Revision 0.3 Updated RCLASS information. ...
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... N : OTES Rev. 0.8 AN296 23 ...
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... AN296 C I ONTACT NFORMATION Silicon Laboratories Inc. 400 West Cesar Chavez Austin, Texas 78701 Tel:1+ (512) 416-8500 Fax:1+ (512) 416-9669 Toll Free:1+ (877) 444-3032 Email: PoEinfo@silabs.com Internet: www.silabs.com The information in this document is believed to be accurate in all respects at the time of publication but is subject to change without notice. ...