MAX5941B PD模块适合多种应用。图1给出了将来自交换机的数据输出连接到中跨输入的典型应用。然后,中跨将电源添加到每一个支持PoE的输出。
本例中,端口1连接到以太网相机,端口2连接到一个无线接入点。当中跨打开(或当器件连接)时,中跨检查每个输出的PoE信号。该模块将端口1及端口2的外设识别为有效的PoE设备,中跨为外设提供数据和电源。 中跨连续监测每个输出,以观察是否已添加或移除有效的PoE设备。由于本例中其他端口没有PoE信号,因此中跨仅向连接的周边设备传递数据。
图1. 典型应用中,来自交换机的数据输出连接至中跨,通过中跨将电源添加到数据线上,实现以太网供电。
特性
兼容IEEE 802.3af
36V至60V输入电压范围
12V/1A输出
无最小负载要求
小尺寸SIL封装
低输出纹波及噪声
高效率用电设备
无需外部电容
可调输出电压
低成本
1500V隔离(输入至输出)
板上“或”逻辑二极管,带外部12V适配器
引脚说明
图2. 引脚排列
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. |
功率分级
功率分级用于PD向供电设备(PSE)指示其自身功率需求的。MAX5941B模块允许通过连接在CP1的CP2之间的电阻外部编程电流分级,如图3所示。如果没有安装电阻器,模块将默认为0级。表2提供了编程电阻值的完整清单。
图3. 设置功率分级时,需在引脚CP1和CP2间接电阻
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 |
可调节输出
MAX5941B PD模块的ADJ引脚可将输出电压在标称值附近上下微调。调节输出电压时,在ADJ引脚与GND或VOUT之间连接电阻(图4)。用公式1和2可计算出实现预期的上调电压及下调输出电压所需的电阻值。
其中VTRIM_UP为预期的上调输出电压,VTRIM_DOWN为预期的下调输出电压。
图4. 调节输出电压时,ADJ引脚与GND之间(上调)或VOUT之间(下调)连接电阻。
图5A. 上调输出电压曲线
图5. 下调输出电压曲线
与外部12V适配器的典型连接
通常情况下,PD与适配器配合使用,每个输出端串接一个二极管,如图6所示。
图6. 传统方案中,用电设备连接到适配器,每个输出端串接一个二极管。
对于MAX5941B PD模块,内置了输出二极管D1。如果PD单独使用,用一个0Ω电阻取代该二极管,以提高效率。图7为板上“或”逻辑二极管D1的位置。
图7. 在MAX5941B PD模块中内部二极管D1的位置
该模块只需要一个外部电容,如图8所示;至少需要1µF陶瓷电容。
图8. 典型连接电路图中,外部电容连接在GND和VOUT之间
电气特性
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 |
工作在超过“极限参数”中所列出的条件下将可能引起模块的永久损坏。这里只指的是极限参数,并不是意味着在这些条件下或超过这些条件下模块能正常工作。器件工作在极限参数条件下过长时间将影响模块的可靠性。
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
图9. 输出纹波和噪声
图10. 开启与关断
图11. 瞬态响应
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 |
变压器设计
图12. 变压器电气原理图
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 |
图13. 变压器构造图
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 |
审核编辑:郭婷
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