Typical Characteristics (continued)
(Circuit of Figure 26 and Figure 32) Figure 13. Minimum Operating Voltage Figure 14. Quiescent Current versus Duty Cycle Figure 15. Feedback Voltage versus Duty Cycle Figure 16. Feedback Pin Current VOUT = 15 V A: Output Pin Voltage, 50 V/div If the DDPAK/TO-263 package is used, the thermal resistance can be B: Output Pin Current, 2 A/div reduced by increasing the PCB copper area thermally connected to C: Inductor Current, 2 A/div the package. Using 0.5 square inches of copper area, θJA is 50°C/W, D: Output Ripple Voltage, 50 mV/div, AC-Coupled with 1 square inch of copper area, θJA is 37°C/W, and with 1.6 or more square inches of copper area, θJA is 32°C/W.
Figure 17. Maximum Power Dissipation (DDPAK/TO-263) Horizontal Time Base: 5 μs/div Figure 18. Switching Waveforms
Typical Characteristics (continued)
(Circuit of Figure 26 and Figure 32) Figure 19. Load Transient Response
7 Detailed Description
7.1 Overview
LM2576 SIMPLE SWITCHER稳压器是一种易于使用的，非同步降压型DC-DC转换器，对于HV版本，其输入电压范围从40V至最高60V。 它具有出色的线路和负载调节能力，能够提供高达3A的DC负载电流。 这些设备提供3.3 V，5 V，12 V，15 V的固定输出电压，以及可调输出版本。 该系列只需要很少的外部元件，其引脚排列是为简单，优化PCB布局而设计的。.
7.2 Functional Block Diagram
regulated DC Input
VIN
1 CIN + Rgulator 4
Feedback Internal ON/OFF 5 ON/OFF R2
R1 + Fixed Gain Error Amp ± + Comparator 3 Amp Switch
1 k ± Driver OUTPUT 2 D1 L1 VOUT + L
1.23 V
BAND-GAPREFERENCE 52 kHZ OSCILLATOR RESET SHUTDOWN LIMIT THERMAL CURRENT 3 COUT O A D GND
3.3 V R2 = 1.7 k 5 V, R2 = 3.1 k 12 V, R2 = 8.84 k 15 V, R2 = 11.3 k For ADJ. Version R1 = Open, R2 = 0 Ω Patent Pending
7.3.1 Undervoltage Lockout
某些应用中，希望保持稳压器关闭，直到输入电压达到某个阈值为止。 图20显示了完成该任务的欠压锁定电路，而图21显示了应用于降压-升压配置的相同电路。 这些电路使稳压器保持关闭状态，直到输入电压达到预定水平为 止。
VTH ≈ VZ1 + 2VBE(Q1) (1)
7.3 Feature Description
Feature Description (continued)
+VIN +VIN LM2576-XX
R1 20 + 1
20 K CIN 5 ON/OFF 3 GND
R2 10 K
Z1 Q1
Complete circuit not shown.
Figure 20. Undervoltage Lockout for Buck Circuit
+VIN
+VIN
R1
+
1LM2576-XX
20 K
20 K CIN 5 ON/OFF 3 GND
R2 10 K
Z1
Q1
-VOUT
Complete circuit not shown (see Figure 24).
Figure 21. Undervoltage Lockout
for Buck-Boost Circuit
7.3.2 Delayed Start-Up
ON / OFF引脚可用于提供如图22所示的延迟启动功能。输入电压为20 V，对于所示的器件值，电路在电路开始切换之前提供大约10 ms的延迟时间。 。 增大RC时间常数可以提供更长的延迟时间，但是过大的RC时间常数可能会通过将纹波耦合到ON / OFF引脚上而导致60 Hz或120 Hz纹波较高的输入电压出现问题。
7.3.3 Adjustable Output, Low-Ripple Power Supply
Figure 23 shows a 3-A power supply that features an adjustable output voltage. An additional LC filter that reduces the output ripple by a factor of 10 or more is included in this circuit. Feature Description (continued)
+VIN +VIN + CD LM2576-XX 1 0.1 …F + 5 ON/OFF 3 GND
CIN 100 …F RD 47 K
Complete circuit not shown.
55 V Figure 22. Delayed Start-Up Feedback
+VIN 4 Unregulated DC Input 1 LM2576HV-ADJ Output L1 Output Voltage
5 CIN
+ 3 GND 100 …F 2 ON/OFF 150 μH D1 1N5822 + COUT R2 50 k 20 μH +1.2 to 50 V @3A
+ C1 2000 …F
1.21 k R1 100 …F
optional output ripple filter
Figure 23. 1.2-V to 55-V Adjustable 3-A Power Supply With Low Output Ripple
7.4.1 Shutdown Mode
The ON/OFF pin provides electrical ON and OFF control for the LM2576. When the voltage of this pin is higher than 1.4 V, the device is in shutdown mode. The typical standby current in this mode is 50 μA.
7.4.2 Active Mode
When the voltage of the ON/OFF pin is below 1.2 V, the device starts switching, and the output voltage rises until it reaches the normal regulation voltage.
7.4.3 Current Limit
The LM2576 device has current limiting to prevent the switch current from exceeding safe values during an accidental overload on the output. This current limit value can be found in the Electrical Characteristics: All Output Voltage Versions under the heading of ICL.
7.4 Device Functional Modes
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