摘要:MAX8538双路同步buck控制器能够提供3A的+5V、-5V输出。利用一个控制器作为同步整流降压(buck)转换,而另一个通过变压器输出负压。电路支持软启动和软关断。
这里提供的1MHz、全陶瓷电容设计方案采用MAX8538双同步buck控制器提供+5V和-5V电源,并具有软启动、软关断功能。控制器配置为同步buck转换,提供+5V @ 3A输出,第二个buck控制器配置为反激转换,通过1:1变压器提供-5V @ 3A输出。
增益为-1/2的运算放大器MAX4400控制负电压输出。MAX8538的内部5V VL线性稳压器为运算放大器提供偏置。增益为-1/2的运算放大器输出限定在此范围内,并在误差放大器的共模限制范围内。
Buck转换器控制增益为:Vout / Vin = 占空比。1:1反激转换器控制增益为:Vout / Vin = 占空比 / (1 - 占空比),随着占空比的增大而增大。对于1:1反激转换器,占空比 = Vout / (Vin + Vout) = 5V / (10.8V + 5V) = 0.317。这样,附加控制增益 = 1 / (1 - 0.317) = 1.464。附加控制增益是影响3类补偿网络设计的一个因素,使单位增益频率降低了1.464倍。运算放大放反相增益通过调节R23补偿,不会影响补偿网络的其它电路。
MAX837电压检测提供欠压闭锁功能。当输入电压Vin大于9.2V时,MAX8538开启。R31引入75mV的正反馈(滞回),可以避免噪声干扰,在较低的Vin摆率下能够提供干净的软启动、软关断过程。注意,由于反激转换器的变压器工作在非连续电流状态下,-5V软关断与+5V波形的对称性取决于-5V电源的负载。另外,-5V侧由于电流不连续,需要连接比+5V输出电容更大的输出滤波电容。

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图1.
表1. VinIinV1I1V2I2Efficiency12.000.0445.0830-5.0430 10.773.415.0783-5.03830.82612.003.065.0803-5.04030.82713.232.795.0803-5.04030.823 20mVpp ripple in 20MHz BW 25mVpp ripple in 20MHz BW
表2. 10.8V至13.2V输入,-5V @ 3A、5V @ 3A输出电路的材料清单9/30/03 DesignationQTYDeSCRJPTionC2,C4310uF 16V X5R ceramic capacitor (1210) Taiyo Yuden EMK325BJ106MNC5,C6,C7,C10, C4150.1uF ceramic capacitor (0603)C12,C307100uF 6V Y5U ceramic capacitor (1210) Taiyo Yuden JMK325E107MMC1314.7uF 6V X5R ceramic capacitor (0805) Taiyo Yuden JMK212BJ475MGC1411uF 25V X5R ceramic capacitor (1206) Taiyo Yuden TMK316BJ105MLC1511uF 6V X5R ceramic capacitor (0603)Taiyo Yuden JMK107BJ105MAC1713.3nF ceramic capacitor (0603)C18,C2025pF ceramic capacitor (0603)C191560pF ceramic capacitor (0603)C2111.5nF ceramic capacitor (0603)C221220pF ceramic capacitor (0603)C23,C24233nF ceramic capacitor (0603)C401680pF ceramic capacitor (0603)C4211.2nF ceramic capacitor (0603)C431470pF ceramic capacitor (0603)D1,D22100mA 30V Schottky diode (SOD-323) Central Semi CMDSH-3D315A 40V Schottky diode Central Semi CMSH5-40L112.2uH 10A Power Inductor Delta THA104-2R2L212.2uH 14.4A Dual Power Inductor Pulse P0395N1,N5,N9330V 13mΩ N-ch MOSFET (SO-8) International Rectifier IRF7821N3,N7230V 30mΩ N-ch MOSFET (SO-8) Fairchild FDS6612AR21511 Ω 1% resistor (0603)R31681 Ω 1% resistor (0603)R712.2 Ω 5% resistor (0603)R814.7 Ω 5% resistor (0603)R9,R24220.0k Ω 1% resistor (0603)R10,R15253.6k Ω 1% resistor (0603)R11151k Ω 5% resistor (0603)R1211.5k Ω 5% resistor (0603)R1314.3k Ω 5% resistor (0603)R14143k Ω 5% resistor (0603)R16,R25210.0k Ω 1% resistor (0603)R2215.1Ω 0.125W 5% resistor (1206)R23124.9k Ω 1% resistor (0603)R2613.3 Ω 0.25W 5% resistor (1210)R27118 Ω 5% resistor (0603)R28133 Ω 5% resistor (0603)R29110.0k Ω 1% resistor (0603)R3011.50k Ω 1% resistor (0603)R311100k Ω 1% resistor (0603)U11MAX8538EEI (28-QSOP)U21MAX4400AXK (5-SC70)U31MAX837EUS (4-SOT143)
本文关键字:陶瓷 电工文摘,电工技术 - 电工文摘