全陶瓷電容設(shè)計(jì)的降壓/反相型3A、+/-5V電源
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這里提供的1MHz、全陶瓷電容設(shè)計(jì)方案采用MAX8538雙同步buck控制器提供+5V和-5V電源，并具有軟啟動(dòng)、軟關(guān)斷功能?？刂破髋渲脼橥絙uck轉(zhuǎn)換，提供+5V @ 3A輸出，第二個(gè)buck控制器配置為反激轉(zhuǎn)換，通過(guò)1:1變壓器提供-5V @ 3A輸出。
增益為-1/2的運(yùn)算放大器MAX4400控制負(fù)電壓輸出。MAX8538的內(nèi)部5V VL線性穩(wěn)壓器為運(yùn)算放大器提供偏置。增益為-1/2的運(yùn)算放大器輸出限定在此范圍內(nèi)，并在誤差放大器的共模限制范圍內(nèi)。
Buck轉(zhuǎn)換器控制增益為：Vout / Vin = 占空比。1:1反激轉(zhuǎn)換器控制增益為：Vout / Vin = 占空比 / (1 - 占空比)，隨著占空比的增大而增大。對(duì)于1:1反激轉(zhuǎn)換器，占空比 = Vout / (Vin + Vout) = 5V / (10.8V + 5V) = 0.317。這樣，附加控制增益 = 1 / (1 - 0.317) = 1.464。附加控制增益是影響3類補(bǔ)償網(wǎng)絡(luò)設(shè)計(jì)的一個(gè)因素，使單位增益頻率降低了1.464倍。運(yùn)算放大放反相增益通過(guò)調(diào)節(jié)R23補(bǔ)償，不會(huì)影響補(bǔ)償網(wǎng)絡(luò)的其它電路。
MAX837電壓檢測(cè)提供欠壓閉鎖功能。當(dāng)輸入電壓Vin大于9.2V時(shí)，MAX8538開啟。R31引入75mV的正反饋(滯回)，可以避免噪聲干擾，在較低的Vin擺率下能夠提供干凈的軟啟動(dòng)、軟關(guān)斷過(guò)程。注意，由于反激轉(zhuǎn)換器的變壓器工作在非連續(xù)電流狀態(tài)下，-5V軟關(guān)斷與+5V波形的對(duì)稱性取決于-5V電源的負(fù)載。另外，-5V側(cè)由于電流不連續(xù)，需要連接比+5V輸出電容更大的輸出濾波電容。
查看大圖
圖1.
表1.
| Vin | Iin | V1 | I1 | V2 | I2 | Efficiency |
| 12.00 | 0.044 | 5.083 | 0 | -5.043 | 0 | |
| 10.77 | 3.41 | 5.078 | 3 | -5.038 | 3 | 0.826 |
| 12.00 | 3.06 | 5.080 | 3 | -5.040 | 3 | 0.827 |
| 13.23 | 2.79 | 5.080 | 3 | -5.040 | 3 | 0.823 |
| 20mVpp ripple in 20MHz BW | 25mVpp ripple in 20MHz BW |
表2. 10.8V至13.2V輸入，-5V ＠ 3A、5V ＠ 3A輸出電路的材料清單9/30/03
| Designation | QTY | Description |
| C2,C4 | 3 | 10uF 16V X5R ceramic capacitor (1210) Taiyo Yuden EMK325BJ106MN |
| C5,C6,C7,C10, C41 | 5 | 0.1uF ceramic capacitor (0603) |
| C12,C30 | 7 | 100uF 6V Y5U ceramic capacitor (1210) Taiyo Yuden JMK325E107MM |
| C13 | 1 | 4.7uF 6V X5R ceramic capacitor (0805) Taiyo Yuden JMK212BJ475MG |
| C14 | 1 | 1uF 25V X5R ceramic capacitor (1206) Taiyo Yuden TMK316BJ105ML |
| C15 | 1 | 1uF 6V X5R ceramic capacitor (0603)Taiyo Yuden JMK107BJ105MA |
| C17 | 1 | 3.3nF ceramic capacitor (0603) |
| C18,C20 | 2 | 5pF ceramic capacitor (0603) |
| C19 | 1 | 560pF ceramic capacitor (0603) |
| C21 | 1 | 1.5nF ceramic capacitor (0603) |
| C22 | 1 | 220pF ceramic capacitor (0603) |
| C23,C24 | 2 | 33nF ceramic capacitor (0603) |
| C40 | 1 | 680pF ceramic capacitor (0603) |
| C42 | 1 | 1.2nF ceramic capacitor (0603) |
| C43 | 1 | 470pF ceramic capacitor (0603) |
| D1,D2 | 2 | 100mA 30V Schottky diode (SOD-323) Central Semi CMDSH-3 |
| D3 | 1 | 5A 40V Schottky diode Central Semi CMSH5-40 |
| L1 | 1 | 2.2uH 10A Power Inductor Delta THA104-2R2 |
| L2 | 1 | 2.2uH 14.4A Dual Power Inductor Pulse P0395 |
| N1,N5,N9 | 3 | 30V 13mΩ N-ch MOSFET (SO-8) International Rectifier IRF7821 |
| N3,N7 | 2 | 30V 30mΩ N-ch MOSFET (SO-8) Fairchild FDS6612A |
| R2 | 1 | 511 Ω 1% resistor (0603) |
| R3 | 1 | 681 Ω 1% resistor (0603) |
| R7 | 1 | 2.2 Ω 5% resistor (0603) |
| R8 | 1 | 4.7 Ω 5% resistor (0603) |
| R9,R24 | 2 | 20.0k Ω 1% resistor (0603) |
| R10,R15 | 2 | 53.6k Ω 1% resistor (0603) |
| R11 | 1 | 51k Ω 5% resistor (0603) |
| R12 | 1 | 1.5k Ω 5% resistor (0603) |
| R13 | 1 | 4.3k Ω 5% resistor (0603) |
| R14 | 1 | 43k Ω 5% resistor (0603) |
| R16,R25 | 2 | 10.0k Ω 1% resistor (0603) |
| R22 | 1 | 5.1Ω 0.125W 5% resistor (1206) |
| R23 | 1 | 24.9k Ω 1% resistor (0603) |
| R26 | 1 | 3.3 Ω 0.25W 5% resistor (1210) |
| R27 | 1 | 18 Ω 5% resistor (0603) |
| R28 | 1 | 33 Ω 5% resistor (0603) |
| R29 | 1 | 10.0k Ω 1% resistor (0603) |
| R30 | 1 | 1.50k Ω 1% resistor (0603) |
| R31 | 1 | 100k Ω 1% resistor (0603) |
| U1 | 1 | MAX8538EEI (28-QSOP) |
| U2 | 1 | MAX4400AXK (5-SC70) |
| U3 | 1 | MAX837EUS (4-SOT143) |
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