Feature description

23 LM2574 series stabilizer is single -chip 3.3V, 5V, 12V, 15V, the output can be adjusted to the voltage switch staber Integrated circuits that provide all active functions can be adjusted for the output voltage range, drive the 0.5A load, with excellent lines and loads 1.23V to 37V (high voltage type 57V) ± 4%. These devices have a fixed output line and load condition voltage of 3.3V, 5V, 12V, 15V, and adjustable

.

The input voltage range is wide, 40V, and a maximum of 60V. The minimum number of external voltage high-voltage version components are required. These regulators simply include internal frequency compensation and fixation-only 4 external component frequency oscillating.

52 kHz fixed frequency internal oscillator LM2574 series provides a high -efficiency TTL shutdown capability, low -power and backup to replace the popular three -terminal linear mode regulator. Because of its high efficiency, copper

The high -efficiency marks on the printing circuit board are usually

using the ready -made standard sensor, only heat dissipation.

A series of standard inductors are limited to heat clearance and current, optimizing the protection of LM2574 can be used for several different manufacturers. This feature greatly simplifies the application design of the switching power supply.

Other features of simple and efficient antihypertension (buck) include the regulator output voltage in the specified input voltage and output load conditions, as well as ± 10%on the oscillator

for the frequency High -efficiency pre -adjuster. Including the external shutdown function

The switch on the card is 50 μA (typical) spare current. The output switch

The Buck Boost includes a cycle -by -cycle current limit, and the full protection conditions of the heat stopping pile during faults.

Typical application (fixed output voltage version)

limit. The work rated value represents the expected function of the device, but does not guarantee specific performance restrictions. Ensure the standards and test conditions, see LM2574-3.3, LM2574HV-3.3 electrical characteristics.

（2） 如果需要军用/航空专用设备，请联系TI销售办事处/经销商以获取可用性和规格

LM2574-3.3、LM2574HV-3.3电气特性

[ 123] Standard surface specifications are suitable for TJ 25 ° C. The black body specifications are suitable for the temperature range of the whole working condition.

(1) at room temperature (standard typeAll the limits specified under the extreme temperature (thick body surface). All room temperature is limited to 100%production test. By using the correlation of the quality control of standard statistics, all the limits (SQC) methods at extreme temperatures are specified. All restrictions are used to calculate the average output quality level.

(2) If external components capture the performance of the diode, inductance, input and output capacitance, it will affect the performance of the switching regulator system. When using LM2574 as shown in the test circuit, the system performance will be like electrical characteristics.

LM2574-5.0, LM2574HV-5.0 electrical characteristics

Standard surface specifications are suitable for TJ 25 ° C, and the black body specifications are suitable for the temperature range of the whole working condition.

(1) All the limits specified at room temperature (standard surface) and extreme temperature (thick body). All room temperature is limited to 100%production test. By using the correlation of the quality control of standard statistics, all the limits (SQC) methods at extreme temperatures are specified. All restrictions are used to calculate the average output quality level.

(2) If external components capture the performance of the diode, inductance, input and output capacitance, it will affect the performance of the switching regulator system. When using LM2574 as shown in the test circuit, the system performance will be like electrical characteristics.

All output voltage versions of the electrical characteristics

Standard surface specifications are suitable for TJ 25 ° C, and the black body specifications are suitable for the temperature range of the whole working condition. Unless there are other regulations, the vehicle recognition number 12V for 3.3V, 5V and adjustable versions; for 12V, vehicle identification number 25V version, 15V version of the vehicle recognition number is 30V. Iload 100 mAh.

(1) All the limits specified at room temperature (standard surface) and extreme temperature (thick body). All room temperature is limited to 100%production test. By using the correlation of the quality control of standard statistics, all the limits (SQC) methods at extreme temperatures are specified. All restrictions are used to calculate the average output quality level.

(2) When the output is short or overload, the frequency of the oscillator is reduced to about 18 kHz, resulting in the output voltage drop from the rated output voltage by about 40%. This self -protection function reduces the average power to dissipate integrated circuits by reducing the minimum duty cycle from 5%to about 2%. Figure 9

(3) Output pin source current. Without a diode, the inductance or capacitor is connected to the output pin.

(4) Remove the feedback foot from the output end and connect to 0V.

(5) Remove the feedback foot from the output end and connect it to+12V (suitable for adjustable, 3.3V and 5V versions) and+25V (suitable for 12V and 15V version). Mandatory shutdown output transistor.

(6) Vehicle identification number 40V (high -voltage type is 60V).

(7) Around the wires with an environmental thermal resistance of about 1 square inch printing circuit board copper. The additional copper area will further reduce thermal resistance. See the application prompts in this data table and the simple software of the hot model of the switch.

(8) The heat resistance to the environment is about 4 square inch and 1 ounce (0.0014 inches). Thick) Printing circuit board copper around clues. The additional copper area will further reduce thermal resistance (see Note 7)

r1 1k

3.3V, R2 1.7k

5V, R2 3.1k

12V, R2 8.84K [ 123]

15V, R2 11.3K

for adjectives. Version

R1 open road, R2 0Ω

Note: The needle number is suitable for 8 -pin PDIP packaging.

cin-22μF, 75 volts

Aluminum electrolytic

COUT-220 μF, 25 volts

Aluminum electrolytic [ 123]

D1-Schottky, 11DQ06

L1-330 μH, 52627

(for 5V input, 3.3V output, use

100 μH, RL-1284 -100)

R1-2K, 0.1%

R2-6.12,000, 0.1%

In any switch regulator,, in any switch regulator, The layout is very important. The voltage of the fast switching current -related voltage -related voltage transition can cause problems. The length of the wire represented by the minimum inductance and grounding circuit should be as short as possible. Single -point grounding or ground flooring should be adopted to achieve the best results. When the adjustable version is used, the programming resistor near the physical positioning regulator is used to keep the sensitive feedback line short circuit.

Input capacitors (CIN)

In order to maintain stability, the regulator input pin must be bypassed at least 22 μF electrolytic capacitors. The leader of this capacitor must be kept short and located near the regulator. If the operating temperature range includes a temperature below -25 ° C, the input capacity may be greater. In most electrolytic capacitors, the capacitor value decreases with the decrease in voltage, and ESR increases the temperature and age with the decrease in voltage. Paided ceramics or solid cavities will improve the stability temperature of the regulator at low temperature. forThe largest capacitor's working life, the rated value of the balanced ripple wave current of the capacitor should be greater than

All the switch regulators in the sensor have Two basic working modes: continuous and discontinuous. The relationship between the two types of the difference is related to the inductance current, whether it is continuously flowing or in the normal switching cycle for a period of time. Each mode has different operating characteristics, which will affect the performance and requirements of the regulator. LM2574 (or any simple switch series) can be used for operation. In many cases, the preferred operation mode is a continuous mode. It provides better load adjustment, lower peak switches, inductance and diode current, and can have lower output ripple voltage. But it really needs a relatively large electrical value to keep the inductive current flowing continuously, especially at low output load current.

In order to simplify the inductance selection process, the inductive selection guidelines (Nuo Mo Mo) (see Figure 25 through Figure 29). This guide assumes that continuous mode operation and select a certain percentage of peak-peak electrical ripple current (ΔIind) as the maximum design load current. At the LM2574 simple switch, the percentage percentage of the peak of the electromotive ripple current (load current) changes with the selection of different design load currents. When the percentage of the inductive ripple current is allowed to increase the low current application, the dimensions and values of the inductance can be kept relatively low. When the inductive ripple current works when the switch works in a continuous mode, the range of the electromot current waveform is triangular to a sawtooth wave type (depending on the input voltage). For the given input voltage and output voltage, the peak amplitude of the inductive current waveform remains unchanged. When the load current rises or decreases, the entire sawtooth current waveform also rises or decreases. The average DC value of this waveform is equal to DC load current (configuration of antihypertensive regulator).

If the load current drops to a sufficiently low level, the bottom of the jagged current waveform will reach zero, and the switch switch will be switched to the non -continuous operation mode. This is a fully acceptable operation mode. If the load current is small enough. The curve shown in FIG. 30 illustrates the peak changes of the inductive ripple current (ΔIind). When selecting different maximum load currents, and when the upper boundary of the working point and the inductance area to the lower boundary (see the inductance selection).

Please consider the following example: Vout 5 volts@0.4 Ann vehicle identification number minimum 10 volts, maximum 20 volts 26 selection guidelines show that for 0.4A load The current, the input voltage range is 10V and 20V, and the inductor area selected by the guide board is 330 μH. This inductance value will allow peaks to peak to peak electrical ripple current (ΔIind) to a percentage of maximum load current. For this sensor value, ΔIind will also change with the input voltage. When the input voltage increases to the upper boundary of the inductive area when the input voltage is increased to 20V, the current ripple current increases. Refers to in the curve of FIG.At the current level, it runs in a 330 μH inductance region with 53%of ΔIND 0.4A or 212MA P P-P. This ΔIIND is very important because this number can determine the peak current current rated circuit of the inductance, the minimum load current required before the non -continuous operation, and the output capacitance, the output ripple voltage can be calculated, or the output ripple voltage and knowing the output ripple voltage and know ΔIND can calculate ESR.

From the previous example, the peak-peak (ΔIind) of the inductive ripple current 212 mia P-P.一旦ΔIND值已知，以下三个公式可用于计算有关开关的附加信息调节器电路：

选择指南选择适合连续模式操作的电感值，但如果电感值选择过高， Designers should investigate the possibility of discontinuous operations. This computer design software switch becomes simple and will provide discontinuous (and as a continuous) operation mode. There are different types of inductors, such as pots, rings, E -type frames, tube tube cores, etc., and there are different iron -hearted materials, such as iron oxygen and iron powder. The cheapest wire core type is composed of metal wire wrapped on the iron oxygen rod core. This structure creates a cheap inductor, but the magnetic flux is not exactly included in the magnetic core, which will produce more electromagnetic interference (EMI). The EML may cause problems with sensitive circuits, or due to the voltage in the sensor probe probe. Select the inductance listed in the table includes the core of the iron powder ring coil for pulse engineering and the core of the iron oxygen line shaft.

The inductor should not exceed its maximum rated current because it may be saturated. When the inductor starts to saturate, the inductance is reduced rapidly, and the inductor starts to look mainly the DC resistance of the winding winding). This can lead to the rapid rise of inductive current and affect the storage capacity of the energy induction, and may cause the inductors to overheat. Different sensor types have different saturation characteristics, and you should remember this when choosing an inductor. The data table of the sensor manufacturer includes current and energy limit to avoid inductance saturation.

Output capacitor

requires an output capacitor to filter the output voltage, and a output capacitor is required to ensure the stability of the ring. The capacitor should be positioned near LM2574 with a short PC trajectory. Standard aluminum electrolytes are usually sufficient, but low ESR types recommend low output ripple voltage and good stability. The ESR of the capacitor depends on many factors, some of which are: value, rated voltage, physical dimensions and type construction. Generally speaking, low -value or low voltage (less than 12V) electrolytic capacitors usually have higher ESR numbers. The size of the output ripple voltage is mainly the amplitude of the output capacitance and inductive ripple current (ΔIind). See inductive ripple current (ΔIind) in the application prompts. Lower capacitance (100 μF-330 μF) usually allows the output ripple voltage from 50 MV to 150 MV, and a larger capacitor reduces the ripples to about 20Malliotic to 50 millivolves. In order to further reduce the output ripple voltage in order to further reduce the output ripple voltage, several standard electrolytic capacitors can be connected to the output ripple voltage. This kind of capacitor is usually called high frequency "