Description

LM2576 The series stabilizer is the ideal choice of single -chip integrated circuit applies to a simple design (antihypertensive converter) for antihypertensive switch staber. All circuits in this series can drive 3.0 -load to have excellent lines and load adjustment functions. These devices have a fixed output voltage of 3.3V, 5.0V, 12V, 15V, and the output voltage can be adjusted. The design purpose of these regulators is to minimize external components to simplify power design. The standard series is the optimized inductor that is optimized by LM2576. Several different sensors makers. Since the LM2576 converter is a switching power supply, its efficiency is significantly higher than the popular three -terminal linearity, especially the regulator with higher input voltage. In many cases, the heat dissipation is very low, no heat sink, or can reduce the size of the heat sink dramatically. The standard series of inductors used with LM2576 can be from several different manufacturers. This function greatly simplifies the design of the switching power supply. The characteristics of LM2576 include ensuring that the output tolerance of ± 4%specifies the voltage in the input voltage and output load conditions, and ± 10%at the frequency of the oscillator (± 2%exceeds 0 ° C to 125 ° C). External shutdown includes 80 μA (typical) available current. The output switch includes a circular current limit, and protection under the condition of complete thermal shutdown failure.

Features

3.3 V, 5.0 V, 12 V, 15 V, and adjustable output publish

Overline and load conditions

Guarantee 3.0 A output current

Wide input voltage range

Only 4 external components

52 KHz fixed frequency internal oscillator

TTL shutdown function, low power standby mode

High efficiency

Use the ready -made standard electrical sensor

Hot shutdown Heat Limited Protection

Application

Simple and high -efficiency antihypertensive regulator

The high -efficiency pre -adjustor of the linear regulator

The switch regulator on the card

]

正-负转换器（降压-升压）

负升压转换器

电池充电器电源

[ 123] Absolute maximum rated value (absolute maximum rated value indicates that the limit may be damaged by the limit.)

Note: You can provide ESD data according to the requirements

The work rated value (the working rated value represents the conditions of the device to play, but do not guarantee specific performance restrictions. Guarantee specifications and test conditionsSee electrical characteristics. )

System parameter ([Note 1] Test circuit diagram 15)

Electric characteristics (unless there are other regulations, 3.3 V, 5.0 V, and adjustable versions VIN 12 V, for the 12 V version, for the 15 V version, VIN 30 V.ILOAD 500 mAh. For the typical value TJ 25 ° C, for the minimum value/maximum value, TJ is a knot for working values applicable Warm range [Note 2], unless there is another instructions.)

Note: 1. If external components capture diodes, inductors, input and output capacitors System performance. When the LM2576 test circuit is used as shown in Figure 15, the system performance is shown in the system parameter part.

2LM2576 test joint temperature range: tlow --40 ° C thigh +125 ° C

Device parameters

Electrical characteristics (unless otherwise regulations, 3.3 v, 3.3 v, 3.3 V. 5.0 V and adjustable versions of VIN 12 V. For the 12 V version, for the 15 V version, vin 30 V.ILOAD 500 mAh. For typical value TJ 25 ° C, for minimum value/maximum value, TJ, TJ The temperature range of the working value [Note 2], unless there is another instructions.)

Note: If the output is short -circuited or overload, the adjustment output voltage is made from nominal voltage from the nominal nominal voltage. The output voltage drops by about 40%. This self -protection function decreases from 5%to about 2%by reducing the minimum duty cycle.

4. Output (pin 2) source current. Without a diode, the inductors or capacitors are connected to the output pin.

5. Feedback (pin 4) Remove and connect to 0 V from the output end.

6. Feedback (needle 4) removed from the output end and connected to +12 V (adjustable), 3.3 v and 5.0 V versions, and +25 V (for version 12 V and 15 V) Version is closed to force output transistors. 7vin 40 volts

Typical performance characteristics (Figure 15 circuit)

] Voltage 15 v

A: output pin voltage, 10 V/DIV

B: Electrochemical current, 2.0 A/DIV

C: inductance current, 2.0 A/DIV, AC coupling

D: output ripple voltage, 50mv/ddiv, AC coupling

Horizontal Foundation: 5 μs/DIV

In any switch regulator, the printing circuit board is very important. The parasitic traces of fast switching current and circuit inductance, bandal capacitors, and printing circuit boards can generate voltage transient electromagnetic interference (EMI) and operations. As shown in Figure 15, the length of the inductance and grounding circuit should be expressed as short as possible with thick wires. In order to obtain the best results, a single -point grounding (as shown in the figure) or the ground floor structure should be adopted. On the other hand, the PCB area is connected to the pin 2 (internal switch transmitter) to minimize the coupling circuit of sensitivity. Another sensitive part of the circuit is feedback. It is important to keep the sensitive feedback line short circuit. To ensure this, the programming resistor is actually located nearby using the adjustable version of the LM2576 regulator.

Buck converter basis

LM2576 is the most basic positive mode converter for antihypertensive or antihypertensive converter. The basic schematic diagram is shown in Figure 16. There are two different time periods for the operation of this regulator. The first occurred in the input terminal of the input voltage when the input terminal was connected to the input end of the inductor. The output of the inductor is the output voltage rectifier (or capture the diode) is reverse bias. During this period, because there was a constant voltage power supply electrical sensor current began to rise linearly, as shown in the following formula:

During this opening period, energy stored in the core magnetic flux form. Whether the sensor is correctly designed, there is enough load requirements during the closure period of energy storage.

The next period is the shutdown period of the power switch. When the power switch is turned off, the inductor reverses its polarity and is fixed on a diode on the ground pipe voltage. The current flows through the capture of the diode, thereby keeping the load current circuit. This will be from the sensor. During this period, the electrical sensor current is:

When the power switch is connected again, the cycle ends. The adjustment of the inverter can be completed in the following ways to change the duty cycle of the power switch. It is possible to describe the duty cycle:

in the formula, T is the switching cycle.

For the buck converter with the ideal element, its occupation ratio

FIG. 17 shows the ideal waveform of the BUCK converter to capture diode voltage and inductance current.

Input capacitance (CIN)

Input capacitors should have a low ESR switch mode converter ESR (equivalent series resistance) aluminum or solid input The pins need to be bypass electric container and ground pins to prevent large voltage transients from appearing at the input end. It must be located near the regulator. In most electrolytic capacitors, the capacitor value decreases, and ESR increases low temperature. When the reliable work is lower than -25 ° C at temperature, the larger value of the input capacitor may be needed. Also with ceramics or solids parallel capacitorsIt will increase the stability temperature of the regulator under cold state.

The average root rated current of CIN

The important parameter of the input capacitor is the valid value current rated value. The capacitor is large, and the large surface area usually has a higher equal square root current rating. For a given capacitance value, the physical capacity of higher voltage electrolytic capacitors will be compared to voltage capacitors, which can dissipate more air around the air, so there will be higher RMS current rated values. The consequences of operating electrolytes exceeding the rated value of the average cubes of the current are shortened. In order to ensure the maximum capacitance working life, the rated of the balance of the cubes of the capacitor should be:

output ripple voltage Low and good stability. ESR is recommended to use output capacitors. There are two main functions of the output capacitor: filtering output and providing regulator loop stability. The peak value of the output capacitor and inductive ripple current is the main factor affecting the voltage value of the output ripple. Standard aluminum electrolytic grooves can meet some but high -quality design and low ESR type recommendation. There are many factors for ESR values of an aluminum electrolytic capacitor, such as capacitor values, voltage rated values, physical dimensions, and structure types. In most cases, the lower the electrolytic capacitor with a higher voltage, the lower the ESR value. Generally, the voltage of the capacitor is much higher. It may require the rated value to provide a low ESR value, that is, the low -output ripple voltage is required. The output capacitor requires the upper limit and lower limit of the ESR value. As mentioned above, the low ESR value requires a low output ripple voltage, usually 1%to 2%of the output voltage. However, if the ESR of the selected capacitor is extremely low (less than 0.05 u0026#8486;), there is a possibility of unstable feedback circuit, and an oscillation is generated at the output end. This situation may occur as the only output capacitance when ESR of the capacitor is very low. At low temperature, the parallel aluminum electrolytic capacitor electrolytic capacitors are not recommended for the temperature below -25 ° C. At low temperature, usually at -40 ° C at -25 ° C, and at -40 ° C, the low-temperature recommended temperature of the solid cavior is lower than -25 ° C. They can be used in parallel with aluminum electrolytic grooves. The capacity of the values 容 electric container should be 10%or 20%of the capacitor of the capacitor. The output capacitor should have at least 52 kHz, and the rated valid validity ripple current ratio ratio ratio ratio-peak-peak electrocatator ripple current.

Capture the diode

Finding the capture diode LM2576 near LM2576 is an antihypertensive converter; it requires a fast diode to provide the return path for the electric sensor current when the switch is turned off. This diode must be located near LM2576 to avoid electromagnetic interference with traces of short -term and short -circuit printing circuits. The use of Schottki or soft switching super fast recovery diode. Because the rectifier diode is the loss of the switching power supply, it is important to choose the design of the rectifier's most suitable converter. The Schottky diode provides the best performance because they cutThe speed of the speed, the slow voltage of the forward speed drops.

They provide the best efficiency, especially at low output voltage applications (5.0 V and below). Another choice can recover quickly or recover the diode in ultra -fast recovery. It is worth noting that some types of diode closing characteristics may cause unstable or electromagnetic interference failure. Fast recovery diode with soft recovery characteristics can better meet some quality and low noise design requirements. Table 1 provides a list regulator for LM2576 for diode. Standard 50/60 Hz rectifier diode, such as 1N4001 series or 1N5400 series is not applicable.

Electrochemical

Magnetic ingredients are the design of the cornerstone switching power supply. The design of the core style and magnetic components has greatly affected the power supply on the overall reliability. Using improperly or improper designs can cause the current in the high -voltage peak switching power supply in the transition rate, and the possibility may occur during abnormal operation. The voltage peak will cause the semiconductor to enter the avalanche breakdown. If enough, the parts will be applied immediately. It may also cause severe radio frequency interference (radio frequency interference) and EMI (electromagnetic interference).

Continuous and discontinuous operation mode

LM2576 antihypertensive converter can be operated in continuous and discontinuous operation. This is a relatively large load, and the performers are continuously flowing through the inductors, and never fall to zero. Under the conditions of light load, the circuit will be forced to be disconnected as the mode time of the inductor current to zero in a certain period of time (see Figure 23 and Figure 24). Each mode has different operating characteristics that affect the performance and requirements of the regulator. The surgical method preferred in many aspects is continuous surgical mode. It provides larger output power, lower peak current switches, induction, and diode, which can have lower output ripple voltage. On the other hand, it does need a larger inductor value to keep the electrical sensor current flowing, especially at low output load current and/or high input voltage to simplify the choice of the inductor. Added to this data table (Figure 18 to 22). This guideline assumes that the regulator runs in the continuous mode, and selects the electromoter ripple current that allows the use of peak inductors to use a certain percentage of the maximum value to design load current. This percentage can be changed to select different design load currents. For light loads (less than about 300 mAh), the regulator may need to be operated in the discontinuous mode, because the inductance value and size can be kept relatively low. As a result, the percentage current of the inductor peak value increases. This discontinuous operation mode is that this type of switch converter can be accepted. If the following situation occurs, the antihypertensive regulator will be forced to enter the discontinuous mode load current.

Select the correct sensor style

some important precautions when selecting the coreThe items are the physical volume that must be accommodated by the core material, cost, and output power power that must be accommodated, and the core of electromagnetic interference (EMI) shielding must be provided. The sensor selection guide covers different types of inductors, such as pot, E -core, ring -shaped and tube tube core, as well as different core materials such as iron oxygen and iron powder manufacturers.

For high -quality design regulators, the core core seems to be the best choice. Because the magnetic flux is included in the core, it produces less electromagnetic interference to reduce problems in the noise sensitive circuit. The cheapest is the core type, which consists of a rod core around the iron oxygen. This type of inductor is open because its core is open, and the magnetic flux is not included in the core. When multiple switching regulators are located in the same printing circuit board, the opening of the magnetic core will cause interference between two or more regulator circuits, especially under high current, due to mutual coupling. A ring, tank core or E -core (closed magnetic structure) is applied to such applications.

Do not operate an inductor that exceeds its range

The maximum rated current that exceeds the power sensor may be overheated by the inductors due to the copper wire, so the magnetic core may be saturated. The core of the rock core is too high, so that the cross -sectional area of the cross -core can no longer support additional magnetic flux lines. This will cause the infiltration rate of the core to decrease the inductance value rapidly, and the sensor begins to work mainly as the main resistance. It only has DC resistance. This will cause the switch current to rise rapidly and force the LM2576 internal switch to recycling the switching current limit, thereby reducing the DC output load current. This may also cause sensors and/or LM2576. Different inductors have different saturations, selecting sensors.

Output voltage ripple and transient

The source of the output ripple

Because LM2576 is the switching power regulator, its output voltage If not filter, it will contain a sawtooth wave voltage at the frequency of switching. The output ripple voltage range is the output voltage. This is mainly an ESR of the ripple current caused by the electrone jagged. The short -voltage peak and the reduction method regulator output voltage may also include the voltage peak at the peak of the short -circuit sawtooth wave (see Figure 25). These voltage peaks appear because of the fast switching action of the output switch, and the inductance of the parasitic output filter capacitor. There are some other important factors, such as line inductors, strange capacitors, and used to evaluate these instantaneous changes, all of which help them with amplitude nails. In order to reduce these voltage peaks, the low -induced response uses capacitors, and its lead length must be kept short. The importance of the quality of printing circuit boards should also be prominent.

Reduce the output ripple

In order to minimize the voltage of the output ripple, this is the inductance value and/or use of the possible amplify the inductors L1 Larger output capacitors. There is another way to pass additional LC too muchFilter (20μH, 100 μF), can be added to the output (see Figure 34) to further reduce the output ripple and transient amount. With such a filter, the output ripple voltage can be 10 times or more. Figure 25 shows the difference between the filtering and the output waveform of the filter and the output waveform. Figure 34 is shown in Figure 34. The lower waveform comes from the converter, and the upper waveform displays the output ripple voltage filter through the additional LC filter.

Precautions for heat dissipation and heat dissipation

Tongkou components to -220LM2576 have two packages, one TO-220 (T, TV) and 5-pin surface installation D2PAK (D2T). Although to -220 (t) components need to keep the LM2576 knot temperature in most cases in most cases. The higher environmental temperature needs to be a radiator or an external heat sink for the printing circuit (PC). The surface is packed and encapsulated D2PAK and its heat dissipation. The surface is installed with D2PAK. It is designed to welded on the copper on the PC board. This copper and circuit board are other components that generate heat from this packaging heat sink, such as the catcher diode and inductor. The copper plate area of the PC board should be at least 0.4 IN2 (or 260 square inch inch). Ideally, it should have 2 square inch or more square inch (1300 mm2) 0.0028 -inch copper. The amount of copper surface with an additional 6.0 square -inch (4000 square mm) has not obvious heat dissipation effects. If further heating needs to be improved, double or multi -layer PCs should consider using large -area copper plates. In order to achieve the best thermal performance, it recommends using wide copper traces and the copper area in the layout of large printing circuit boards. The only exception is the output (switch) foot, which should not have a large area of copper (see page 8 PCB layout guide ). To determine whether the radiator is needed. First of all: 1.PD (MAX) maximum regulator power consumption application. 2.TA (maximum) maximum ambient temperature application. 3.TJ (maximum) maximum allowed temperature (LM2576 is 125 to 125 ° C). For conservative design, the highest knot temperature should not exceed 110 ° C to ensure safety operations. Each increase of the temperature at the+10 ° C connection can withstand it, and the estimated service life parts are halved. 4. 4. RθJC packaging thermal resistance connection box. 5.Rθja packaging thermal resistance -ambient temperature. (Refer to the absolute maximum rated board on page 2 of this data or RθJC and RθJA value). Consumption power: PD (VIN X IQ)+D X Iload x vsat where D is the duty ratio, for the buck converter

IQ (static current) and vsat can be possible In LM2576 product introduction, VIN is the minimum input voltage applied, VO is the regulator output voltage.Iload is a load current. The dynamic switch loss during the switching process can be ignored if the dynamic switching loss is used in appropriate types. For independent applications that do not use the radiator (independent) on the radiator, the temperature can be determined by the following conclusions: TJ (Rθja) (PD)+TA type (RθJa) (PD) indicates the knot temperature Caused by dispersing power, the maximum environmental temperature of TA. If the actual work temperature on the radiator is greater than the selected safety work, the temperature is determined in step 3, and a radiator is needed. The temperature calculation at the junction is as follows: TJ PD (Rθja+RθCS+RθSA)+TA formula, RθJC is a thermal resistance-condition, RθCS is the heat resistance situation-radiator, and RθSA is the heat resistance radiator-ambient temperature.

If the actual operating temperature is greater than the selection of safe running temperature, the larger value requires a radiator. Several aspects of the heat design should be noted that the thermal resistance and temperature increase value of the packaging are similar values, and there are many factors that affect these numbers, such as PC board size, shape, thickness, physical location, location, board temperature, and surrounding surroundings The air is moving or static. Other factors are the width of the trace lines, the total amount of copper, the thickness of the copper, the thickness of the copper, the single -sided or double -sided, the amount of solder on the multi -layer plate and even the color traces of the board. The size, quantity and spacing of other components can also affect its effectiveness to dissipate and heat.

Other applications

Reverse Developer

Use the reverse pressure boost boost regulator of LM2576–12 as shown in Figure 26 as shown Show. The voltage between the negative output voltage between the positive input and the public grounding of the circuit is used to the negative output voltage by guiding the regulator to the negative output voltage. By ground feedback pins, the regulator induced reverse output voltage and adjust. In this example, LM2576–12 is used to generate -12 V output. In this case, the maximum input voltage cannot exceed +28 V, because the maximum voltage appears in front of the supervisor is that the input and output voltage must be limited to the maximum 40 V. This circuit configuration can provide about 0.7A when the input voltage is 12V or higher. The minimum input voltage required for a lighter load is reduced to about 4.7 volt, because the healog of the pressure -proof regulator topology can generate an absolute output voltage value, which is greater than or less than the input voltage.

Because the switching current is lower than the standard BUCK converter topological structure in this buck-boost configuration, it is lower. This downstream-boosting inverter can also require a larger startup input current, even if light load. This may make the input power overload current limit less than 5.0 A. AT needs such input startup currents at least 2.0 ms or longer. The actual time depends on the voltage and size of the output output capacitor. Because a relatively high start -up current through the topology structure of this inverter, a delayed recommendation starts or underwritten locking circuit is adopted. MakeUse a delay to start the device, and the input capacitor can be charged to a higher voltage regulator to start working before switching mode.

The high input current required for startup is now provided by CIN input. It has been mentioned above that the lax delay or underwriting atresia may be very useful. The delayed startup circuit is applied to the Buck-Buost converter as shown in Figure 27, Figure 33 in the section of the IOU Lock describes the IOU locking function topology structure of the same converter.

Design Suggestions:

The working method of the inverter regulator and the BUCK converter and other different design programs are used to select the inductors L1 or output capacitor COUT. The output capacitance value must be greater than the actual value. It is usually used for the buck converter design. Low input voltage or high output current requires a large value output capacitor (within thousands of μF). The recommended inductor range inverter converter is designed between 68 μH and 220 μH to select an inductor with an appropriate rated current. Use the following formula to obtain the peak electrocompany Current:

Under the working conditions under normal continuous inductor current, the worst situation occurs when the vehicle recognition number is minimum [123 ]

For the reverse configuration, the on/off pin requires some horizontal conversion techniques. This is in fact, the ground pins of the converter IC are no longer located in the ground. At present, the ON/OFF pin threshold voltage (1.3V) must be related to the negative voltage level. There are many different possible ways to close, two of which are shown in Figure 28 and 29

negative lift pressure regulator

This example is buck- A variant of the Boost topology is called a negative booster regulator. This regulator switch current is relatively high, especially at a lower current input voltage. Internal switching current limits leads to lower output load current capabilities. The circuit in Figure 30 shows the negative boost configuration. The input voltage range in this application is from -5.0 V to -12 V, and provides a adjustable -12 V output. If the input voltage is greater than -12 V, the output will rise higher than -12 V, but it will not damage the regulator.

Design suggestions: The same design rules as the previous reversal can use the Buck-Boost converter. The output capacitor must choose a standard lower -voltage converter that requires greater requirements than what requires. Low input voltage or high output current requires a large value output capacitor (thousands of μF within the range). The recommended range of the negative booster regulator of the inductors and the design of the inverter converter. Another important point is that these negative promoting converters cannot provide a current -limiting load protection in the middle. If there are short circuits in the output, other methods, such as as a fuse, may need to provide load protection.

Delay startup

There are some applications, such as mentioned on the inverter regulator, which requires a higher number of startup current. In this case, the input power supply is very useful if this delay startup function is very useful. When the time for the application voltage and output voltage appears, the circuit in Figure 31 can be used. As the input application voltage, the capacitor C1 is charged, and then the voltage on the resistor R2 drops. When the voltage is on/off, the regulator is started when the threshold is below the threshold 1.3 V. The resistor R1 is used to limit the maximum voltage that is applied to the on/off pin. It reduces the high sensitivity of the power supply, and it also limits the C1 discharge current of the capacitor, but it is not forced to use. When the ripple voltage is existed with 50 Hz or 60 Hz (100 Hz or 120 Hertz), long -delay can coupling the ripples to the opening/level will cause some problems. Double) Frequency

Impurd voltage lock

Some applications require that the regulator is kept closed until the input voltage reaches a certain threshold level. FIG. 32 shows the underwriter locking circuit regulator applied to Buck. A version of the Buck-Buost converter circuit is shown in Figure 33. The resistor R3 keeps the ON/OFF pins, keep the regulator off until the input voltage reaches the predetermined threshold level of the ground. Under the working conditions of inductive current, the worst situation occurs when the vehicle recognition number is the smallest.

adjustable output, low ripple power supply

The output current capacity is 3.0 A. It is characterized by the output voltage, as shown in Figure 34 as shown in Figure 34 Essence The regulator provides output from 3.0 A to 1.2 V to 35 V. This input voltage range is about 3.0 V to 40 V. In order to reduce the output ripple 10 times or more times more than the additional L -C filter in this circuit.