8.2.1 Fixed Output Voltage Version
8.2 Typical Applications
+VIN Feedback
LM2576HV- Fixed Output 1 4 Output 2 5 L1 VOUT UNREGULATED VIN
+ 100 …F 100 μH DC INPUT
GND 3 + CIN ON/OFF COUT D1 1000 μF
MBR360 L O A D
CIN — 100-μF, 75-V, Aluminum Electrolytic COUT — 1000-μF, 25-V, Aluminum Electrolytic
D1 — Schottky, MBR360
L1 — 100 μH, Pulse Eng. PE-92108 R1 — 2 k, 0.1% R2 — 6.12 k, 0.1%
Figure 26. Fixed Output Voltage Versions
8.2.1.1 Design Requirements
Table 1 lists the design parameters of this example.
Table 1. Design Parameters
DESIGN PARAMETER Regulated Output Voltage (3.3 V, 5 V, 12 V, or 15 V), VOUT Maximum Input Voltage, VIN(Max) Maximum Load Current, ILOAD(Max) EXAMPLE VALUE 5 V 15 V 3 A
8.2.1.2 Detailed Design Procedure
8.2.1.2.1 Custom Design with WEBENCH Tools
单击此处使用WEBENCH?Power Designer创建自定义设计。 1.首先输入您的VIN，VOUT和IOUT要求。
2.使用优化器转盘针对诸如效率，占地面积和成本之类的关键参数优化设计，并将该设计与德州仪器（TI）的其他可能解决方案进行比较。
3.WEBENCH Power Designer为您提供了定制的原理图以及具有实时定价和组件可用性的材料清单。
4.在大多数情况下，您还可以：
–进行电气仿真，以查看重要的波形和电路性能， –运行热仿真以了解您的板的热性能，
–将自定义的原理图和布局导出为流行的CAD格式， –打印设计的PDF报告，并与同事共享您的设计。
8.2.1.2.2 Inductor Selection (L1)
1. Select the correct Inductor value selection guide from Figure 27, Figure 28, Figure 29, or Figure 30. (Output
voltages of 3.3 V, 5 V, 12 V, or 15 V, respectively). For other output voltages, see the design procedure for the adjustable version. Use the selection guide shown in Figure 28.
2. From the inductor value selection guide, identify the inductance region intersected by VIN(Max) and
ILOAD(Max), and note the inductor code for that region. From the selection guide, the inductance area intersected by the 15-V line and 3-A line is L100.
3. Identify the inductor value from the inductor code, and select an appropriate inductor from the table shown in
Figure 27. Part numbers are listed for three inductor manufacturers. The inductor chosen must be rated for operation at the LM2576 switching frequency (52 kHz) and for a current rating of 1.15 × ILOAD. For additional inductor information, see the Inductor Selection section. Inductor value required is 100 μH from the table in Figure 27. Choose AIE 415-0930, Pulse Engineering PE92108, or Renco RL2444.
8.2.1.2.3 Output Capacitor Selection (COUT)
1. The value of the output capacitor together with the inductor defines the dominate pole-pair of the switching
regulator loop. For stable operation and an acceptable output ripple voltage, (approximately 1% of the output voltage) TI recommends a value between 100 μF and 470 μF. COUT = 680-μF to 2000-μF standard aluminum electrolytic was chosen.
2. The voltage rating of the capacitor must be at least 1.5 times greater than the output voltage. For a 5-V
regulator, a rating of at least 8 V is appropriate, and a 10-V or 15-V rating is recommended. Capacitor voltage rating = 20 V. Higher voltage electrolytic capacitors generally have lower ESR numbers, and for this reason, it can be necessary to select a capacitor rated for a higher voltage than would normally be needed.
8.2.1.2.4 Catch Diode Selection (D1)
1. The catch-diode current rating must be at least 1.2 times greater than the maximum load current. Also, if the
power supply design must withstand a continuous output short, the diode must have a current rating equal to the maximum current limit of the LM2576. The most stressful condition for this diode is an overload or shorted output condition. For this example, a 3-A current rating is adequate.
2. The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage. Use a 20-V
1N5823 or SR302 Schottky diode, or any of the suggested fast-recovery diodes shown in Table 3.
8.2.1.2.5 Input Capacitor (CIN)
An aluminum or tantalum electrolytic bypass capacitor located close to the regulator is needed for stable operation. A 100-μF, 25-V aluminum electrolytic capacitor located near the input and ground pins provides sufficient bypassing.
8.2.2 Application Curves
Figure 27. LM2576(HV)-3.3 Figure 28. LM2576(HV)-5.0
8.2.3 Adjusted Output Voltage Version
Figure 29. LM2576(HV)-12 Figure 30. LM2576(HV)-15 Figure 31. LM2576(HV)-ADJ
+VIN Feedback
1 LM2576HV- ADJ 4 Output L1 VOUT 5 V UNREGULATED 7 V ± 60 V + 100 …F 2 5 100 μH DC INPUT
GND 3 + CIN ON/OFF COUT R2 L
D1 MBR360 1000 μF O R1 D A
where
VREF = 1.23 V, R1 between 1 k and 5 k
Figure 32. Adjustable Output Voltage Version
8.2.3.1 Design Requirements
Table 2 lists the design parameters of this example.
Table 2. Design Parameters
DESIGN PARAMETER Regulated Output Voltage, VOUT Maximum Input Voltage, VIN(Max) Maximum Load Current, ILOAD(Max) Switching Frequency, F
8.2.3.2 Detailed Design Procedure
8.2.3.2.1 Programming Output Voltage
Select R1 and R2, as shown in Figure 32. Use Equation 5 to select the appropriate resistor values.
EXAMPLE VALUE 10 V 25 V 3 A Fixed at 52 kHz
R1 can be between 1 k and 5 k. (For best temperature coefficient and stability with time, use 1% metal film resistors)
R2 = 1 k (8.13 ? 1) = 7.13 k, closest 1% value is 7.15 k
8.2.3.2.2 Inductor Selection (L1)
1. Calculate the inductor Volt ? microsecond constant, E × T (V × μs), from Equation 8:
(5)
(6)
(7)
VOUTE u TV INV OUT
V1000
IN u F IN KHZ
V u V
2. Calculate E × T (V × μs):
E u T 25 10 u 10 u 1000 115 V u V
25 (9) 52
3. Use the E ? T value from the previous formula and match it with the E × T number on the vertical axis of the
inductor value selection guide shown in Figure 31. E ×(10) T = 115 V × μs
4. On the horizontal axis, select the maximum load current.
(8)
ILOAD(Max) = 3 A (11)
5. Identify the inductance region intersected by the E × T value and the maximum load current value. Note the
inductor code for that region. Inductance Region = H150
6. Identify the inductor value from the inductor code, and select an appropriate inductor from the table shown in
Table 4. Part numbers are listed for three inductor manufacturers. The inductor chosen must be rated for operation at the LM2576 switching frequency (52 kHz) and for a current rating of 1.15 × ILOAD. For additional inductor information, see the Inductor Selection section. Inductor Value = 150 μH. Choose from AIE part #415-0936, Pulse Engineering part #PE-531115, or Renco part #RL2445.
8.2.3.2.3 Output Capacitor Selection (COUT)
1. The value of the output capacitor together with the inductor defines the dominate pole-pair of the switching
regulator loop. For stable operation, the capacitor must satisfy :
IN M
C OUT t 13,300 )
V OUT uL +
AX
V
yields capacitor values between 10 μF and 2200 μF that satisfies the loop requirements for stable operation.
To achieve an acceptable output ripple voltage, (approximately 1% of the output voltage) and transient response, the output capacitor may need to be several times larger than yields.
25
COUT t 13,300 22.2 )
10 u 150
However, for acceptable output ripple voltage select: COUT ≥ 680 μF
COUT = 680-μF electrolytic capacitor
2. The voltage rating of the capacitor must be at last 1.5 times greater than the output voltage. For a 10-V
regulator, a rating of at least 15 V or more is recommended. Higher voltage electrolytic capacitors generally have lower ESR numbers, and for this reason, it can be necessary to select a capacitor rate for a higher voltage than would normally be needed.
8.2.3.2.4 Catch Diode Selection (D1)
1. The catch-diode current rating must be at least 1.2 times greater than the maximum load current. Also, if the
power supply design must withstand a continuous output short, the diode must have a current rating equal to the maximum current limit of the LM2576. The most stressful condition for this diode is an overload or shorted output. See Table 3. For this example, a 3.3-A current rating is adequate.
2. The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage. Use a 30-V
31DQ03 Schottky diode, or any of the suggested fast-recovery diodes in Table 3.
8.2.3.2.5 Input Capacitor (CIN)
An aluminum or tantalum electrolytic bypass capacitor located close to the regulator is needed for stable operation. A 100-μF aluminum electrolytic capacitor located near the input and ground pins provides sufficient bypassing.
Table 3. Diode Selection Guide VR 20 V 3 A 1N5820 MBR320P SR302 1N5821 MBR330 31DQ03 SR303 1N5822 SCHOTTKY 4 A to 6 A 3 A FAST RECOVERY 4 A to 6 A 1N5823 30 V 50WQ03 1N5824 40 V MBR340 31DQ04 SR304 MBR350 31DQ05 SR305 MBR360 DQ06 SR306 MBR340 50WQ04 1N5825 The following diodes are all rated to 100-V 31DF1 HER302 The following diodes are all rated to 100-V 50WF10 MUR410HER602 50 V 50WQ05 60 V 50WR06 50SQ060
IKSEMI高压三端稳压器IL2576HV-12D2T-P-奥伟斯 - 图文
