基于MAX5941B PWM控制器的用電設(shè)備（PD）模塊參考設(shè)計(jì)
MAX5941B PD模塊適合多種應(yīng)用。圖1給出了將來自交換機(jī)的數(shù)據(jù)輸出連接到中跨輸入的典型應(yīng)用。然后，中跨將電源添加到每一個(gè)支持PoE的輸出。
本例中，端口1連接到以太網(wǎng)相機(jī)，端口2連接到一個(gè)無線接入點(diǎn)。當(dāng)中跨打開(或當(dāng)器件連接)時(shí)，中跨檢查每個(gè)輸出的PoE信號。該模塊將端口1及端口2的外設(shè)識別為有效的PoE設(shè)備，中跨為外設(shè)提供數(shù)據(jù)和電源。 中跨連續(xù)監(jiān)測每個(gè)輸出，以觀察是否已添加或移除有效的PoE設(shè)備。由于本例中其他端口沒有PoE信號，因此中跨僅向連接的周邊設(shè)備傳遞數(shù)據(jù)。
圖1. 典型應(yīng)用中，來自交換機(jī)的數(shù)據(jù)輸出連接至中跨，通過中跨將電源添加到數(shù)據(jù)線上，實(shí)現(xiàn)以太網(wǎng)供電。
特性
兼容IEEE 802.3af
36V至60V輸入電壓范圍
12V/1A輸出
無最小負(fù)載要求
小尺寸SIL封裝
低輸出紋波及噪聲
高效率用電設(shè)備
無需外部電容
可調(diào)輸出電壓
低成本
1500V隔離(輸入至輸出)
板上“或”邏輯二極管，帶外部12V適配器
引腳說明
圖2. 引腳排列
| Pin Number | Name | Description |
| 1 | VA1 | Rx Input (1) This input pin is used in conjunction with VA2 and connects to the center tap of the transformer connected to pins 1 and 2 of the RJ45 connector (Rx)—it is not polarity sensitive. |
| 2 | VA2 | Tx Input (2) This input pin is used in conjunction with VA1 and connects to the center tap of the transformer connected to pins 3 and 6 of the RJ45 connector (Tx)—it is not polarity sensitive. |
| 3 | VB1 | Direct Input (1) This input pin is used in conjunction with VB2 and connects to pins 4 and 5 of the RJ45 connector—it is not polarity sensitive. |
| 4 | VB2 | Direct Input (2) This input pin is used in conjunction with VB1 and connects to pins 7 and 8 of the RJ45 connector—it is not polarity sensitive. |
| 5 | CP1 | Class Programming (1) Connecting an external resistor to CP2 will change the current class of the module. With no resistor fitted the module will default to Class 0. |
| 6 | CP2 | Class Programming (2) Connecting an external resistor to CP1 will change the current class of the module. With no resistor fitted the module will default to Class 0. |
| 7 | GND | Ground The ground return for the output. |
| 8 | VOUT | DC Output This pin provides the regulated output voltage from the DC-DC converter. |
| 9 | ADJ | Output Adjust The output voltage can be adjusted from its nominal output by connecting an external resistor from this pin to either the VOUT pin or GND pin. |
| 10 | N.C. | No Connection This pin is not connected internally. |
功率分級
功率分級用于PD向供電設(shè)備(PSE)指示其自身功率需求的。MAX5941B模塊允許通過連接在CP1的CP2之間的電阻外部編程電流分級，如圖3所示。如果沒有安裝電阻器，模塊將默認(rèn)為0級。表2提供了編程電阻值的完整清單。
圖3. 設(shè)置功率分級時(shí)，需在引腳CP1和CP2間接電阻
| Class | Programming Resistance (Ω) | Minimum Power (W) | Maximum Power (W) |
| 0 | Do not fit | 0.44 | 12.95 |
| 1 | 770 | .44 | 3.84 |
| 2 | 388 | 3.84 | 6.49 |
| 2 | 388 | 3.84 | 6.49 |
| 3 | 242 | 6.49 | 12.95 |
| 4 | 161 | Reserved | Reserved |
可調(diào)節(jié)輸出
MAX5941B PD模塊的ADJ引腳可將輸出電壓在標(biāo)稱值附近上下微調(diào)。調(diào)節(jié)輸出電壓時(shí)，在ADJ引腳與GND或VOUT之間連接電阻(圖4)。用公式1和2可計(jì)算出實(shí)現(xiàn)預(yù)期的上調(diào)電壓及下調(diào)輸出電壓所需的電阻值。
其中VTRIM_UP為預(yù)期的上調(diào)輸出電壓，VTRIM_DOWN為預(yù)期的下調(diào)輸出電壓。
圖4. 調(diào)節(jié)輸出電壓時(shí)，ADJ引腳與GND之間(上調(diào))或VOUT之間(下調(diào))連接電阻。
圖5A. 上調(diào)輸出電壓曲線
圖5. 下調(diào)輸出電壓曲線
與外部12V適配器的典型連接
通常情況下，PD與適配器配合使用，每個(gè)輸出端串接一個(gè)二極管，如圖6所示。
圖6. 傳統(tǒng)方案中，用電設(shè)備連接到適配器，每個(gè)輸出端串接一個(gè)二極管。
對于MAX5941B PD模塊，內(nèi)置了輸出二極管D1。如果PD單獨(dú)使用，用一個(gè)0Ω電阻取代該二極管，以提高效率。圖7為板上“或”邏輯二極管D1的位置。
圖7. 在MAX5941B PD模塊中內(nèi)部二極管D1的位置
該模塊只需要一個(gè)外部電容，如圖8所示；至少需要1μF陶瓷電容。
圖8. 典型連接電路圖中，外部電容連接在GND和VOUT之間
電氣特性
| Parameter | Min | Typ | Max | Units |
| DC Supply Voltage | -.3 | 60 | V | |
| DC Supply Voltage Surge for 1ms | -.6 | 80 | V | |
| Storage Temperature | -40 | +100 | °C |
工作在超過“極限參數(shù)”中所列出的條件下將可能引起模塊的永久損壞。這里只指的是極限參數(shù)，并不是意味著在這些條件下或超過這些條件下模塊能正常工作。器件工作在極限參數(shù)條件下過長時(shí)間將影響模塊的可靠性。
| Parameter | Min | Typ | Max | Units |
| Input Supply Voltage | 36 | 48 | 60 | V |
| Undervoltage Lockout | 30 | 36 | V | |
| Operating Temperature | -40 | 25 | +85 | C° |
| Parameter | Min | Typ | Max | Units |
| Nominal Output Voltage (Without the ORing Diode) | 11.76 | 12 | 12.24 | V |
| Output Current | 0 | 1 | A | |
| Output Ripple and Noise | 250 | mV | ||
| Efficiency Without the ORing Diode (48V Input, 1A Output) | 85 | % | ||
| Efficiency with the ORing Diode (48V Input, 1A Output) | 82 | % | ||
| Isolation Voltage | 1500 | V |
波形
圖9. 輸出紋波和噪聲
圖10. 開啟與關(guān)斷
圖11. 瞬態(tài)響應(yīng)
器件列表
| Designation | Qty | Description |
| C1, C2, C6, C17 | 4 |
10μF 25V ceramic capacitor 1206 TDK C3216X5R1E106K MURATA GRM31CR61E106KA12 |
| C3 | 1 |
6800pF 100V ceramic capacitor 0603 TDK C1608X7R2A682K |
| C4 | 1 | 100pF 50V ceramic capacitor 0603 |
| C4 | 1 | 100pF 50V ceramic capacitor 0603 |
| C5, C7, C23 | 1 | 0.1μF 50V ceramic capacitor 0603 |
| C9 | 1 |
10μF 100V aluminium electrolytic capacitor SANYO 100CE10FS |
| C9 | 1 |
10μF 100V aluminium electrolytic capacitor SANYO 100CE10FS |
| C10 | 1 |
1000pF 1.5kV ceramic capacitor 1808 TDK C4520X7R3D102K |
| C12, C25 | 2 |
0.1μF 100V ceramic capacitor 1206 TDK C3216X7R2A104K |
| C13 | 1 |
220μF 25V aluminium electrolytic capacitor SANYO 25CE220FSA |
| C14 | 1 |
1000pF 100V ceramic capacitor 0805 TDK C2012X7R2A102K |
| C19 | 1 |
2.2μF 10V ceramic capacitor 0603 MURATA GRM188R61A225KE34 |
| C22 | 1 | 680pF 50V ceramic capacitor 0603 |
| C28 | 1 | 4700pF 50V ceramic capacitor 0603 |
| D1, D2 | 1 | Bridge rectifier DIODES HD01-T |
| D4, D6 | 2 | Diode 200mA 250V SOD323 DIODES BAV21WS |
| D5, D13 | 2 | 60V Schottky rectifier SMA DIODES B360A |
| D7 | 1 | SMT LED Lamp 0603 FAIRCHILD QTLP600C-Y |
| D8 | 1 | Transient Voltage Suppressor DIODES SMAJ54A |
| R1 | 1 | 20Ω ±1% resistor 0603 |
| R5 | 1 | 270mΩ ±1% resistor 1206 |
| R9 | 1 | 470Ω ±1% resistor 0603 |
| R10 | 1 | 10Ω ±1% resistor 1206 |
| R11, R17 | 2 | 10kΩ ±1% resistor 0603 |
| R12 | 1 | 20kΩ ±1% resistor 0603 |
| R14 | 1 | 25.5kΩ ±1% resistor 1206 |
| R15 | 1 | Not Used |
| R16 | 1 | 0Ω ±1% resistor 1206 |
| R18 | 1 | 1kΩ ±1% resistor 0805 |
| R22 | 1 | 9.53kΩ ±1% resistor 0603 |
| R23 | 1 | 2.49kΩ ±1% resistor 0603 |
| R24, R31 | 2 | 2.5kΩ ±1% resistor 0603 |
| R25, R27 | 2 | 1kΩ ±1% resistor 0603 |
| R26 | 1 | 4.75kΩ ±1% resistor 0603 |
| R28 | 1 | 33kΩ ±1% resistor 0805 |
| R30 | 1 | 4.7Ω ±1% resistor 0805 |
| Q1 | 1 | MOSFET 150V SO-8 IR IRF7465TR |
| U2 | 1 | IC Optocoupler NEC PS2801-1-F4-R-A |
| U3 | 1 | IC VREF 2.5V 0.4% SOT-23 AAC AZ431AN-A |
| U5 | 1 | PWM controller for PD MAXIM MAX5941BESE |
| R30 | 1 | Transformer NP:NS:NB = 35:16:20 LP = 122μH GA3271-AL Coilcraft |
變壓器設(shè)計(jì)
圖12. 變壓器電氣原理圖
| Parameter | Conditions | Value |
| Electrical Strength | 50Hz 1 minute, from pins 1–3, 10–12 to pins 5–8 | 1500VRMS |
| Primary Inductance | Pins 1, 12; all windings open. Measure at 275kHz |
120μH ±10% |
| Primary Leakage Inductance | Pins 1, 12; rest of pins shorted. Measure at 275kHz | 3μH (max) |
| Item | Description |
| 1 | Core: EFD15, PC40. Manufacturer: TDK |
| 2 | Bobbin: EFD15 coil former (SMD), 12 pins |
| 3 | Tape: 8.9mm wide insulation tape |
| 3 | Tape: 8.9mm wide insulation tape |
| 3 | Tape: 8.9mm wide insulation tape |
| 4 | Magnet Wire: .25mm diameter with 150°C |
| 5 | Magnet Wire: .27mm diameter with 150°C |
| 6 | Magnet wire: 0.10mm diameter with 150°C |
| 7 | Varnish |
| Note | All wires include insulation |
圖13. 變壓器構(gòu)造圖
| Step | Description |
| Primary NP1 | Start at pin 1. Wind 35 turns of item 4 in approximately 1 layer. Finish on Pin 12 |
| Insulation | Use 1 layer of item 3 for insulation |
| 12V Winding | Start at pins 6 and 5. Wind 16 turns of 2 parallel strands of item 5. Finish at pins 7 and 8 |
| Insulation | Use 1 Layer of Item 3 for Safety Insulation |
| Primary NP2 | Start at pin 2. Wind 35 turns of item 4 in approximately 1 layer. Finish on pin 11 |
| Insulation | Use one layer of item 3 for safety insulation |
| Bias Winding | Start at pin 3. Wind 20 turns of item 6. Spread turns evenly across bobbin. Finish at pin 10 |
| Outer Wrap | Wrap Wwndings with 2 layers of item 3 |
| Final Assembly | Assemble and secure core halves. Varnish impregnate with item 9 |
審核編輯：郭婷
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