Function description

LM2595 series stabilizer is a single -chip type

3.3V, 5V, 12V, and adjustable output publishing. Circuit

The adjustable output voltage range is used for antihypertensive (antihypertensive) switch regulator. The lines and loads

Conditions. These devices have fixed output

to provide TO-220 and TO-263 (surface voltage is 3.3V, 5V, 12V, and adjustable output Mount) software package.

Make sure the 1A output load current requires the minimum number of external

input voltage range of up to 40V components, these regulators are simple

Including internal frequency compensation #8224; and, and and, and, and, and, to and, to and, and, to, and,, to #8224;, and, and,, to, and, to, Only 4 external components are required to fix the frequency oscillator.

excellent lines and load adjustments

LM2595 series work under the switch frequency specification of 150 kHz, so smaller filters

150 kHz fixed frequency internal oscillation The component component is lower than required

TTL closing capacity frequency switching regulator. Provide standard 5 lead to 220 packaging, with multiple low -power standby modes, IQ is usually 85 μA

Different lead bend options, and 5 lead to 263

surface paste packaging. Generally, for the output voltage

, a ready -made standard electrocompany below 12V, the ambient temperature is lower than 50 ° C, and does not require a radiator.

Hot shutdown and current limit

Protection standard series inductors can use several different manufacturers to apply the LM2595 series. This function greatly simplifies the design of the switching power supply.

Simple and efficient antihypertensive (buck)

Other characteristics of the regulator include tolerance to tolerance of ± 4%

specifically the output voltage at the input voltage and linear adjustment; linear adjustment The high -efficiency pre -adjustor of the device

output load conditions, and the ± 15%

card on the oscillator switch adjustment regulator frequency. Including external shutdown, characteristic is that the positive and negative converter is usually 85 μA spare current. Self -protection characteristics include the current restrictions on the output switch to reduce the output switch and the temperature stop failure condition that is fully protected under the following conditions.

LM2595-3.3 Electrical features

Standard surface specifications are suitable for TJ u003d 25 ° C, and the black body specifications are suitable for the temperature range of the whole working condition.

(1) The typical value is 25 ° C, which represents the most likely standard value.

(2) All limits specified at room temperature (standard surface) and extreme temperature (literal) at extreme temperatures. All room temperature is limited to 100%production test. All limits at extreme temperatures are specified by the correlation of standard statistical quality control (SQC). All restrictions are used to calculate the average shipment quality level (AOQL).

(3) External components, such as capturing diode, inductors, input and output capacitors, and voltage programming resistors, can affect the performance of the switch regulator system. When using LM2595, as shown in Figure 21 test circuit, the system performance will be shown in the system parameters of the electrical characteristics.

LM2595-5.0 electrical characteristics

Standard surface specifications are applicable to TJ u003d 25 ° C, and black body specifications are suitable for the temperature range of the whole working condition.

(1) The typical value is 25 ° C, which represents the most likely standard value.

(2) All limits specified at room temperature (standard surface) and extreme temperature (literal) at extreme temperatures. All room temperature is limited to 100%production test. All limits at extreme temperatures are specified by the correlation of standard statistical quality control (SQC). All restrictions are used to calculate the average shipment quality level (AOQL).

(3) External components, such as capturing diode, inductors, input and output capacitors, and voltage programming resistors, can affect the performance of the switch regulator system. When using LM2595, as shown in Figure 21 test circuit, the system performance will be shown in the system parameters of the electrical characteristics.

All output voltage versions of the electrical characteristics

Standard surface specifications are suitable for TJ u003d 25 ° C, and the black body specifications are suitable for the temperature range of the whole working condition. Unless there are other regulations, for 3.3V, 5V and adjustable versions, vin u003d 12V; for 12V version. Iload u003d 200 mia

(1) The typical value is 25 ° C, which represents the most likely standard value.

(2) All limits specified at room temperature (standard surface) and extreme temperature (literal) at extreme temperatures. All room temperature is limited to 100%production test. All limits at extreme temperatures are specified by the correlation of standard statistical quality control (SQC). All restrictions are used to calculate the average shipment quality level (AOQL).

(3) When the second -level current limit is activated, the switching frequency is reduced. Reduce the severity of the current overload.

(4) There is no diode, and the inductors or capacitors are connected to the output pin.

(5) Remove and connect to 0V from the output end to force output transistors.

(6) Remove the feedback pin from the output end and connect to 12 volts for 3.3 volts, 5 volts and adjustments. For the 12V version, the 15V output transistor is turned off.

All output voltage versions of the electrical characteristics (continued)

Standard surface specifications are suitable for TJ u003d 25 ° C, and the black body specifications are suitable for the temperature range of the whole working condition. Unless there are other regulations, for 3.3V, 5V and adjustable versions, vin u003d 12V; for 12V version. Iload u003d 200 mia

(7) vin u003d 40 volts.

(8) The environmental thermal resistance (no external heat sink) packed in the vertical installation of to-220 is welded to the printing circuit board with a copper area (1 ounce) about 1 square inch.

(9) Welded the TO-263 packaging label to a 0.5-inch (1 ounce) printing circuit board and connected to the environmental hot-resistant copper area.

(10) The TO-263 packaged convex ear welding was welded on the single-sided printing circuit board (1 copper area.

[113] (11) Packing convex ear welding to double-sided printing On the circuit board, the copper area of u200bu200bthe LM2595S side of the ambient thermal resistance connecting board, and the copper area of u200bu200babout 16 IN2 on the other side of the P-C board. Typical performance features (Figure 21 circuit)

pin function

+This is the positive input power supply of the IC switch regulator. A suitable input bypass capacitor must be used to minimize the voltage transient and provide the required switch current regulator. Circuit ground.

Output internal switch. The voltage at this pin is switched between (+vin vsat) and about 0.5V. The duty cycle is about VOUT/VIN. Try to reduce the coupling of sensitive circuits, the area of u200bu200bthe PC board connected to the pin should be maintained at the minimum value. The feedback sensor adjustment output voltage to complete the feedback circuit. , Thereby reducing the total current input power supply current to about 85 μA. Pull the pins to about 1.3V below the threshold voltage to open the regulator and pull this to 1.3V (maximum 25V) to close the regulator to lie down. If you do not need to be grounded, you can keep it on the ground. In any case, the regulator will be in an connection.

Outside the external componentCapital

CIN-Between the input pin and the ground pins requires a low ESR aluminum or 钽 bypass electrical container. It must be located near the regulator. The capacitor prevents large voltage transients from appearing at the input terminal, and provides the instantaneous current required when the switch is turned on. The important parameter of the input capacitor is the voltage rated value and the balance of the average root current. Because the relatively high -level square root current flowing in the input capacitor of the antihypertensive regulator, the average root current rated value of the capacitor should be selected instead of its capacitance or voltage rated value, although the electrical capacity and voltage rated value and the average amount and the average amount are on the balance. Founded current rated value is directly correlated. The average root current rated value of the capacitor can be regarded as the rated power of the capacitor. The equity -based root current passes through the ESR inside the capacitor to generate power, so that the internal temperature of the capacitor stands up. The rated of the balance of the capacitor's balance of the base root current determines that the amount of current required to increase the internal current determines that the temperature is about 10 ° C higher than the ambient temperature of 105 ° C. The dissipation ability of the capacitor to the surrounding air will determine the current that the capacitor can bear safely. The capacitors are large in physical size and large surface area, and usually have a high balance -based root current rated value. In order to give a given capacitor value, higher voltage electrolytic capacitors are more physical than low -voltage capacitors, and therefore can emit more calories to the surrounding air, so it has a higher average root current rated value. If the rated current of the electrolytic capacitor is higher than the average square root value, the operation time life will be shortened. The higher temperature will accelerate the evaporation of the electrolyte of the capacitor and eventually lead to failure. Selecting the input capacitor requires consulting the manufacturer's data table to obtain the maximum allowable valid value wave current. For the maximum ambient temperature of 40 ° C, the general guidance principle is that the rated value of the ripple current is about 50%of the DC load current. When the ambient temperature is as high as 70 ° C, A for conservative design, the rated current is 75%of the DC load current is a good choice. The rated voltage of the capacitor must be at least 1.25 times the maximum input voltage, and usually the high voltage capacitor needs to meet the requirements of the average root current. The chart shown in FIG. 26 shows the value of the electrolytic capacitor, its rated voltage, and the rated equalized square root current. These curves are reliable electrolytic capacitors designed by the Nichicon ""PL"" series of low ESR and high ESR Nichicon ""PL"" series. Other capacitor manufacturers provide similar types of capacitors, but be sure to check the capacitor data table. ""Standard"" electrolytic capacitors usually have higher ESR values, lower -balance -rooted current current fixed values u200bu200band shorter service life.

Surface stickers are widely used for input bypass due to the advantages of small volume and excellent performance, but they must abide by several preventive measures. If a small amount of solid pillar container exceeds the rated value of the excitation surge, it may be short -circuited. When the input voltage rises suddenly, this situation may occur, and higher input voltage will generate higher excitation surge. Several electric container manufacturers have the possibility of minimizing the surge in product current. If the current is turned on, it is estimated,It may be necessary to choose a capacitor with higher voltage capacitors. Like aluminum electrolytic capacitors, the size of the cubic rippling rated current must be adapted to the load current.

Feming capacitor

(adjustment voltage type) When the output voltage is greater than 10 volts or the blood sink of the COUT is very low. The capacitor increases the binding compensation to increase phase margin for the feedback loop to obtain a better loop stability. For the choice of CFF, see the design program section.

Output capacitor

requires an output capacitor to filter output and provide the stability of the regulator circuit. Low impedance or low ESR electrolytic or solid 钽 capacitors used for switching regulator applications. When the output capacitor is selected, the important capacitor parameters are: 100 kHz equivalent series resistance (ESR), the rated value of the average root ripper, the voltage rated value, and the capacitor value. For output capacitors, the ESR value is the most important parameter. The output capacitor requires an ESR value with an upper limit and lower limit. For low output ripple voltage, A requires a low ESR value. The value is determined by the maximum allowable output ripple voltage, usually 2%of the 1%output voltage. However, if the ESR of the selected capacitor is extremely low, the feedback circuit may be unstable, resulting in output oscillation. Using the capacitor or similar types listed in the table will provide a design solution under all conditions. If a very low output ripple voltage (less than 15 millivolves), see the ripples and transients of the rear ripple filter of the output voltage part. The ESR value of the aluminum electrolytic capacitor is related to the capacitor value and its rated voltage. In most cases, in this case, the ESR value of higher voltage electrolytic capacitors is low (see Figure 27). Generally, the capacitor may require a higher voltage rated value to provide a low ESR value required for low output ripple voltage. In many different switching designs, the output capacitance can often only meet three or four different capacitors and several different rated voltages. See the fast design component to select Table 2 and Table 4 to list typical capacitor values, voltage rated values u200bu200band manufacturer's capacitor types. Electrolytic capacitors are not recommended in environments with temperature below 25 ° C. During the cold state, ESR rising temperatures are usually 3 times when 25 ° C, and 10 times when 40 ° C. See the curve shown in Figure 28.

The solid electric container has better ESR specifications at low temperatures, and it is recommended to be used for lower than 25 ° C.

Capture the diode

When the switch is turned off, the antihypertensive regulator requires a diode to provide a return path to the inductor current. This must be a fast diode, and the traces of short -drawing and short printing circuits must be located near LM2595. Due to its very fast switch speed and low positive electricityFor voltage drop, the Schartki diode provides the best performance, especially at low output voltage applications (5V and below). Super fast recovery is still a good choice for high -efficiency rectifies, but some types with sudden cut -off characteristics may cause unstable or electromagnetic interference problems. The reverse recovery time of the super fast recovery diode is usually 50ns or less. The rectifier should not be used because the 1N5400 series is too slow.

Sensor selection

All the switching regulators of the sensor have two basic working modes: continuous and discontinuous. The difference between the two types is related to the current of the electrical sensor, whether it is continuously flowing or if it drops to a period of time in the zero normal switching cycle. Each mode has different operating characteristics, which will affect the performance and requirements of the regulator. Most switch designs will interrupt mode when the load current is low. LM2595 (or any simple relationship column) can be used for operation.

In many cases, the preferred operation mode is a continuous mode. It provides larger output power, lower peak switch, inductance and diode current, and can have a lower output ripple voltage. However, it does require a larger inductor value that keeps the sensor current continuously flowing, especially at low output load current and/or high input voltage. In order to simplify the selection process of the inductors, the electrical sensor selection guide (Nuo Mo Mo) (see Figure 22 Figure 22). This guide assumes that the regulator runs in the continuous mode and selects an induction device to maximize the design load current to a percentage of a percentage of peak to peak electrocarchers ripple current. The percentage of the ripple current of the peak to the peak value is not fixed, but it is allowed to change to select different design load currents. (See Figure 29.)

By allowing the percentage of the ripple current of the low -load current, the percentage of the ripple current of the electrical device can be kept relatively low. When working in a continuous mode, the electrical sensor current waveform types from triangle to jagged waveforms (depending on the input voltage). The average value of this current waveform is equal to DC output load current. The inductor has different styles such as pots, ring, E -type core, and line axis. There are also different core materials, such as iron oxygen and iron powder. The cheapest, line shaft, rod or rod core, including line around the iron oxygen line shaft. This structure makes the inductance cheap, but because the magnetic flux is not completely included in the core of the magnetic core, it will produce more electromagnetic interference (EML). This magnetic flux will induced the voltage sensor to the nearby printing circuit trajectory, which will cause the problem of the two circuits to switch the regulator operation and the nearby sensitive circuit, which may give the wrong range reading, because the inductive voltage in the oscilloscope probe. Please refer to the Core Electric Sensor Section. When multiple switching regulators are located on the same PC board, the opening of the magnetic core will cause interference between two or more regulator circuits, especially under high current. The ring or E -core sensor (closed magnetic structure) should be used in these cases. Select the inductor listed in the table includes Schott's iron oxygen E -type magneticThe core structure is used for iron powder ring for pulse engineering. The maximum current rated value exceeding the inductors may cause the inductors to be overheated due to copper wires, otherwise the magnetic core may be saturated. If the inductor starts to be saturated, the inductance is reduced rapidly, and the inductor starts to look mainly the resistance (the DC resistance of the winding). This will cause the switching current to rise rapidly, forcing the switch to enter a cycle of current limit, thereby reducing the DC output load current. This also causes sensors and/or LM2595 overheating. Different inductors types have different saturation characteristics, and you should remember this when choosing an inductor. The data table of an inductor manufacturer includes current and energy restrictions to avoid the saturation of the inductors.

Intermittent mode operation

Selecting Guide Selecting the inductance value application and/or high input voltage suitable for continuous mode operation but applicable to low current. The intermittent mode design may be a better choice. It requires a smaller physical inductor, and only requires half to one -third of the continuous mode design of the required electrical sense. In discontinuous design, peak switches and electrical sensor currents will be higher, but in these low load currents (400 mAh below), the maximum switching current will still be smaller than the switch current limit. The non -continuous operation of the voltage waveform is very different from the continuous design. The output pin (switch) waveform may have some damping sine bells. (See the typical performance characteristics of the picture, the titles are the non -continuous mode switching waveform.) This bell is caused by non -continuous rather than the instability of the feedback circuit. In intermittent operations, when the switch or diode is not turned on for a period of time, the electric sensor current drops to zero. During this period, a small amount of energy can cause this unique ringtone between the electrical sensor and the switch/diode parasitic capacitor. Under normal circumstances, this kind of bell is not a problem, unless the amplitude becomes larger than the input voltage, even so, there is almost no energy damage. Different types of inductors and/or magnetic core materials produce different numbers of characteristics of this characteristic. The iron heart loss of the iron oxygen magnetic core electromotor is very small, so the bell produced the most. The iron powder's high -speed rail loss electrostatic sensor produces less sounds. If necessary, the series RC can be connected in parallel with an inductor to suppress it. Computer -assisted design software Switchers Make Simple (Version 4.3) will provide values u200bu200bof continuous and discontinuous operation mode of all components.

output voltage ripples and transients

The output voltage of the switching power supply working in the continuous mode will contain the voltage at the frequency of sawtooth wave switch. It may also contain a short -voltage spike waveform at the peak of jagged waves. The output ripple voltage is a function capacitor of the electrical sensor jagged wave current and output ESR. The typical output ripple voltage range is about 0.5%to 3%of the output voltage. When obtaining a low -ripple voltage, the ESR of the output capacitor must be very low, but when the ESR capacitor is used, because they will affect the stability of the circuit and cause the oscillation problem. If a very low output ripple voltage (less than 20Netal), it is recommended to use a rear ripple filter.(See Figure 21.) The inductor required is usually between 1 μH and 5 μH, and the DC resistance is low to maintain good load regulations.Low ESR output filter capacitors also need to ensure good dynamic load response and ripples.The ESR of this capacitor may be expected because it is outside the regulator feedback circuit.The photo shown in FIG. 30 shows a typical output ripple voltage with no rear ripple filter.When observing the output ripples with an oscilloscope, a short, low -induced oscilloscope probe must be used to connect.Most oscilloscope probe manufacturers provide a special probe terminal, welded on the adjustment board, and it is best to be at the output capacitor.This provides a very short -range ground ground, which eliminates the problem of clear and accurate problems related to the problem of 3 -inch grounding lines that is usually equipped with the probe.