General description

lm2678 The series stabilizer is a single -piece integrated circuit that provides all active functions for a downwriting switch stabilizer. The voltage of 5A has a load with excellent lines and load adjustment characteristics. By using the resistance DMOS power switch. This series includes a fixed output voltage of 3.3V, 5V, and 12V, which can be announced. The simple switch concept provides a complete use of the minimum number of external components for design. A high -fixed frequency oscillator (260kHz) allows a component with smaller physical sizes. The sensors used by standard families with LM2678 have the following manufacturers that have greatly simplified the design process. The LM2678 series also has built -in heat shutdown, and the current -limiting and power -capacity opening/off control input will reduce the regulator to the low static backup current conditions of 50 Weian. The output voltage guarantees within the range of ± 2%. The clock frequency is controlled within ± 11%.

Features

Nitrogen efficiency is as high as 92%

Simple design (using ready -made external components)

120 mΩDMOS output switch

3.3 3.3 V, 5V, and 12V fixed output, which can be adjusted (1.2V to 37V) version

The spare current when the Wei'an closed

± 2%full line and the maximum output tolerance [123 123 ]

Condition

Wide input voltage range: 8V to 40V

260 kHz fixed frequency internal oscillator

40 to+125 ° C working knot Temperature range

Application

Simple design, high efficiency ( gt; 90%) antihypertensive switch regulator

Effective linear voltage system pre -regulator

[

[ 123] The regulator

Battery charger

Absolutely maximum rated value (Note 1)

Input power supply voltage 45V

Open/customs lead Foot voltage-0.1V to 6V

The switch voltage is connected -1V to the vehicle identification number

Breathing pins voltage vsw+8V

Feedback pin voltage -0.3V to until 14V

Internal limit of power consumption

ESD (Note 2) 2 kV

Storage temperature range -65 ° C to 150 ° C

Welding temperature

Waves 4 seconds, 260 degrees Celsius

Infrared 10 seconds, 240 degrees Celsius

Qi Phase 75 seconds, 219 degrees Celsius

Rate of running

]power supplyVoltage 8V to 40V

Concluding temperature range (TJ) –40 303C to 125 303C

The electrical characteristics of black bodies are suitable for the entire knot temperature

working range,- 40 303C to 125 303C. Normal type specifications are suitable for TA TJ 25 303C.

All output voltage versions

Electrical characteristics

The limit of thick body font display is suitable for the entire working temperature range, -40 ° C to 125 ° C. The specifications displayed by the standard font are suitable for TA TJ 25 ° C. Unless there are other regulations, the VIN 12V version and the 12 -volt version of the vehicle identification number 24 volts for 3.3V, 5V and adjustable.

Note 1: The absolute maximum rated value refers to the limit value that the device may be damaged. The work rated value indicates where the device is under the condition. Operation rating does not mean guarantee performance restrictions. For guarantee performance limit and related test conditions, please refer to the characteristic table.

Note 2: ESD uses human models, 100PF capacitors are distributed to each pin through 1.5kΩ resistors.

Note 3: The typical value is determined by TA TJ 25 ° C, which represents the most likely standard value.

All output voltage versions

Electrical characteristics (continued)

Note 4: All limits are guaranteed at room temperature (standard surface) and extreme temperature (thick body) Down. All room temperature is limited to 100%test during the production process, TA TJ 25 ° C. By using standard quality control (SQC) to ensure all the limit methods at extreme temperatures. All restrictions are used to calculate the average output quality level (AOQL).

Note 5: The 7 -line vertical installation of the 220 -packaged environmental thermal resistance (no external radiator) connector, the socket or PC has a board with the smallest copper area of 1/2 inch lead.

Note 6: The environmental thermal resistance (no external radiator) connecting to 220 packaged by the vertical installation, 1/2 -inch lead is welded to about 4 square inch (1 ounce) around the PC board guide line Copper area.

Note 7: 7 to-263's environmental thermal resistance head horizontally installed on a 0.136 square inch PC board (with -263 packaging) 1 ounce (0.0014 inches) copper.

Note 8: 7 Diren to the-263 environmental thermal resistance connecting head, and is installed horizontally on a PC plate (0.0014 inches) on PC plates of 0.4896 square inch (3.6 times area). Thick) Copper.

Note 9: 7 wires to the environment thermal resistance of -263, and the horizontal is installed at 1.0064 square inch (7.4 times in

to-263

The area of packaging) is 1 ounce (0.0014 inches. Thick) copper. The additional copper area will further reduce thermal resistance. See the heat model in the switch to make Simple #174; software.

Note 10: The environmental thermal resistance connector of the 14 -lead LLP installed on the PC plate copper area is equal to the mold connecting blades.

Note 11: The environmental thermal resistance connecting the 14 -lead LLP installed on the PC board copper area and connect to the second layer of copper (equivalent to the mold installation baffle. The additional copper area will be used. Further reduce thermal resistance. For relevant layout suggestions, please refer to the application annotation AN-1187.

Program prompt

LM2678 provides a lower -voltage switch stabilizer. The internal force switch is a DMOS power MOSFET design with a high -current capacity design, up to 5A, and efficiently running.

LM2678 is a part of the power converter of the simple switch series. A complete design uses the minimum number of external components. These components are pre -determined by different manufacturers. Version 2.0) Become a complete switching power supply can be quickly designed. Software has provided free, and the output of the power MOSFET switch is directly to the input voltage. Control of the device (PWM). The internal clock inside the PWM controller is fixed to 260kHz oscillator. In the standard antihypertensive application, the ratio of the output voltage of the power supply to the power supply output voltage to the input voltage. 1 The voltage on the vehicle identification number (VIN) and the switch switch through the external voltage to drop the Schottky diode (closed).

Input

The input voltage of the power supply is connected to the pin 2 . In addition to providing energy to the load, the input voltage also provides bias for the internal circuit of LM2678. In order to ensure performance, the input voltage must be 8V to 40V in the voltage range. Located near the pin 2.

C pressure

The capacitor must be connected from the pin 3 to the switch output, the pin 1. This capacitor increases the grid driving force to the internal MOSFET than Vin than Vin Open it completely. This micro switch can reduce the conduction loss of the power switch to the minimum efficiency. The recommended value of the C BOOST is 0.01 micro F.

This is the grounded ground of all components Reference is connected in the power supply. It is recommended to use wide connection ground planes to reduce the entire circuit in the rapid switch, large current application (such as applications with LM2678)Signal coupling

Feedback

This is the input of a two -level high -gain amplifier, which drives the PWM controller. The needle foot 6 must be connected to the actual output voltage of the power supply set by DC output. For fixed output equipment (3.3V, 5V and 12V output), the output is directly connected to the internal gain setting the resistor LM2678. The DC output voltage is required for the outer settings of the adjustable output publishing book 2. To stabilize the operation of the power supply, it is necessary to prevent the coupling of any inductance magnetic flux and feedback input.

Open/Guan

This input provides power supply. Putting this foot or connecting to any voltage less than 0.8V will completely turn off the regulator. The current consumption of the input power supply is only 50 μA. Foot 7 has an internal pull current source of about 20 μA and a 7V to protect clamping clamping Qina diode ground. The voltage level under the condition when the electric driver is turned on/off the foot should not exceed 6V. When you do not need to be controlled/off, the pin 7 should be kept open.

DAP (LLP package)

mold connection pad (DAP) can be connected to the PCB ground plane/island. Relevant CAD and assembly guidelines

The power design of LM2678 greatly simplifies the recommended external components. The extensive inductance, capacitance, and Schottky diode manufacturer have been evaluated to cover all functions (input voltage, output voltage and load current). Simple design uses the line diagram and component table provided in this data table to draw the power of work design without ash. Alternatively, design software, LM267XSIMPLE (version 6.0), can also be used to provide instant component selection, circuit performance computing evaluation, material list component list, and circuit schematic diagram.

A single component from different manufacturers still uses only a small sample that can be used in a small sample. And these suggestions are not only used for designed components. After carefully comparing the component specifications, other manufacturers of equivalent equipment can replace applications. The explanation of each external component and line diagram and selection table is as follows.

sensor

The inductor is the key component of the switching voltage. In order to improve the efficiency, the inductor stores energy on time during the switch, then transfers the energy to the load, and the switch is broken. The line diagram is used to select the inductance value required under a given working conditions. Noomu assumes that the circuit is a continuous work mode (the current flowing through the sensor will not fall to zero). Select the size of the inductance to maintain the maximum ripple current to 30%of the maximum load current. If the ripple current exceeds 30%of the limit choice, the value is larger.

The inductor provided is specially manufactured to provide appropriate operation input output voltage and load current under all operating conditions. Several parts of partsFor a certain amount of inductance. Two sides

Provide installation and passing installations. The three manufacturers of sensors have their own unique characteristics. RENCO: Electricity of iron oxygen rod core; the advantage is usually the lowest cost, which can inherit the ripples and transient peak currents higher than the rated value. These sensors have an external magnetic field, which may produce electromagnetic interference. Pulse engineering: iron powder ring magnetic core inductance; they can also withstand currents higher than the rated current, as ring inductor, low electromagnetic interference. Coil: Electricity of iron oxygen magnetic drum magnetic core; these are the smallest physical dimensions sensors, which are used as surface installation parts. These inductors also generate electromagnetic interference, but less than the sensor.

Output capacitor

The output capacitor plays a smooth and DC output voltage and provides energy storage. The selection of the output has a capacitor (ESR) with related equivalent series resistors, which affects the stability of the output ripple voltage and the control loop. The output ripple voltage of the power supply is a capacitor ESR and an inductive ripple current. This choice of the types of capacitors recommended in the table are low because of blood sinking. In addition, the surface stickers are installed with capacitor and Tongkong aluminum electrolytic capacitors as a solution. The frequency stability of the entire control circuit affects the bipolar in the feedback circuit together with the inductors. In addition, the capacitance and ESR value are zero. These frequency response effects are mobilized with the compensation circuit of LM2678 with the internal frequency LM2678. The general rules of the stable switch and stabilizer circuit The unit gain bandwidth of the circuit is limited to one -sixth of the controller switching

Application prompt (continuation)

frequency. Fixed 260kHz switching frequency LM2678, select the output capacitor to provide the maximum gain bandwidth of the unit to 40kHz. Each recommendation is selected to achieve this result. In some cases, multiple capacitors need to reduce the ESR of the output capacitor to minimize the output ripple (assume that the ripple voltage is 1%or smaller performance conditions of VOUT), or increase the output capacity to reduce the gain bandwidth of the closed -loop unit ( Reduce more than 40kHz). When the parallel combination of a capacitor is to assume that each capacitor is exactly the same. The output capacitance of the balance of the equity and the working voltage (WV) rated value is also an important consideration. In a typical antihypertensive switching voltage voltage, the inductive ripple current (set to 30%inductance selection of not exceeding the maximum load current) is the output capacitor. The average cubes of the capacitor must be greater than this ripple current. The rated voltage output capacitor should be greater than 1.3 times the maximum output voltage of the power supply. If the operation requires a high temperature system, the rated voltage of the capacitor can be reduced to lower than the temperature rated value of the nominal room. It is important to carefully check that the working voltage of the manufacturer decreases with the decrease in temperature.

Enter a capacitor

The rapid change current in the large current switching voltage voltage voltage volume exerts major dynamic load sources to the uncontrolled electricity. The input capacitor helps provides additional current to the power and smooth input voltage change.Like the output capacitor, the input key technical index electric container is a balanced range of the rated current and working voltage. The average root current of this flowing capacitor is equal to half of the maximum DC load current, so the capacitor should have the ability to deal with this problem. Multiple capacitors increase the rated current of total capacity in proportion. The rated voltage should also be selected at 1.3 by the maximum input voltage. According to the unrelated input power supply, the maximum input voltage may be significantly higher than the normal operation under the light load conditions. When choosing, the input capacitor should be considered.

The input capacitor should be placed in a needle that is close to the LM2678 place. Because the relative current runs in the case of rapid transient changes, the input -connected inductance connection cable or PCB trajectory may be transmitted to other parts of the output or circuit. It may be necessary to add a small value (0.1 to 0.47 μF) ceramic capacitors with the input capacitor parallel to prevent or reduce any ringtone. Capture the diode when the power switch is turned off in LM2678, the current passs through the sensor continues to flow. This route current is connected to the diode output and ground between the connections between the switches. This positive bias diode is shifted to switch output to the voltage smaller than ground. This negative voltage must be greater than -1V, so the voltage drop is very low (especially at high current levels). It is recommended to use the Shawki diode. The total efficiency of the entire power supply is significantly affected by the power loss in the diode. The average current of capturing diode depends on the duty cycle (D) of the switch (D), which is equal to the number of load current (1-D). Use the voltage reduction and power loss in the diode required by the actual application of the rated current. During the connection, the diode will be reversed through the input voltage. The reverse voltage rated value of the diode should be at least 1.3 times larger than the maximum input.

Breathing capacitor

The voltage capacitor generates a voltage to drive the grid that drives the internal power MOSFET. This can improve the power loss of the driver resistance through the minimum switch. For all applications, it is recommended to use 0.01 μF/50V ceramic capacitor. When the output voltage is greater than about 6V, the minimum input voltage is greater than about 50%, and the designer's selection of the output filter component. When the application for these specific operating conditions is lower than the current limitation of the fault conditions, the huge lag in the current limit can be observed. This will affect it until the load current is reduced to the allowable flow -limiting protection circuit to reset itself.

Under the current limitation conditions, LM267X is designed to respond in the following ways:

1. When the inductive current reaches the current limit threshold, the connection pulse is terminated immediately. This will happen under any application conditions.

2. However, the current limit block is also designed to temporarily reduce the duty cycle to less than 50%to avoid secondary resonance oscillation, which may cause sensor saturation.

3. Since then, once the inductive current drops to the current limit threshold,During this period, a small relaxation time gradually increased to more than 50%of the specified value. If the output capacitor is large enough, it may be that the output capacitor charging current may be large when the output is tried to recover, and it is enough to repeat the direct touch circuit resolution before the output is fully recovered. As the output increases, this situation is more severe voltage settings, because the energy requirements of the output capacitor change with the square of the output voltage (1/2 cubic centimeter 2), so the charging current needs to be increased. A simple test to determine whether this condition exists in the output of suspicious applications in the converter, and then eliminates short -circuit output conditions. With the correctly selected external component, the output will be restored smoothly. The practical value experiment of external components found that the good temperature of the good working conditions under these specific operating conditions is 47 μF, L 22 μH pay attention. Even if these components are used, the maximum load current large current limits the possibility of magnetic stagnation for the current limit of the device. It is iClim/2. For example, if the input is a 24 -volt output voltage to 18V, the maximum current required is 1.5A, and the current limit of the selected switch must be at least 3A.

Application prompt (continued)

A complete antihypertensive regulator can be designed with a line diagram and table (or available design software) in this data table (or available design software). A step of.

Step 1: Define the power supply working conditions:

The required output voltage

Maximum DC input voltage

Maximum output load current

Step 2: Set out the output voltage LM2678 (3.3V, 5V, or 12V application) by selecting a fixed output settings or determining the adjustable LM2678-adjustment

Step 3: Use four column diagrams, Figure 3 to Figure 6. Table 1 provides specific manufacturers and part numbers for inductive motors.

Step 4: Use Table 3 (fixed output voltage) or Table 6 (adjustable output voltage) to determine the output capacity required for stable operation. Table 2 provides a specific capacitor type selected by the manufacturer.

Step 5: Determine a fixed input capacitor output voltage application from Table 4. Use Table 2 to find the type of capacitor. For adjustable output circuits, a capacitor with sufficient rated work voltage (WV) from Table 2 is greater than the maximum vehicle identification number, and the balance of the rated current of the balance is greater than half of the maximum load current (2 or more capacitors may need to be connected in parallel to connect To.

Step 6: Select a diode from Table 5. The current rated diode must be greater than the maximum load rated voltage must be greater than the maximum vehicle identification number.

Step 7: In design

Fixed output voltage design example

The system logic power bus of 3.3V will come from the wall adapter that provides 13V to 16V -free DC voltage voltage voltage voltage. Essence The maximum load current is 4A. The first choice of Tongkou components.

Step 1: The operating conditions are:

vout 3.3 volts

Maximum vehicle recognition number 16v

Iload maximum value 4a

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123] Step 2: Select LM2678T-3.3. The output voltage will be ± 2%at the temperature of the tolerance, and the temperature range of ± 3%when the full load is run.

Step 3: Use a line diagram of 3.3V device, Figure 3.16V horizontal line (maximum vehicle identification number) and 4A vertical line (ILOAD MAX) indicate a 15μH sensor L46. From in Table 1, you can find RENCO from the part number RL-1283-15-43 in Tongkou components.

Step 4: Use Table 3 to determine the output capacitor. With a 3.3V output and 15 μH inductors, there are four pores of the same type of output capacitor solution and the connected electrical container and its identification code. Table 2 provides actual capacitor characteristics.

The following options will work in the circuit:

2 x 220 μF/10V Sanyo OS-Con (code C5)

2 x 820μF/16V Sanyo MV-GX (Code C5)

1 x 3900 μF/10V nickel -hydride battery (code C7)

2 x 560 μF/35V Panasonic HFQ (code C5)

Step 5: Use tables using tables 4 Select the input capacitor. 3.3 There are three types of hole solutions for infusion and 15 μH. These capacitors provide sufficient rated voltage and average cubes rated current greater than 2A (maximum 1/2 ILOAD). Agen uses Table 2 for specific component characteristics

The following choices are suitable:

2 x 680 μF/63V Sanyo MV-GX (code C13)

1 x 1200 μF/63V nickel -metal hydride battery (code C25)

1 x 1500 μF/63V Panasonic HFQ (code C16)

Step 6: From Table 5, 5A or more Schartky diode must be necessary Picked out. For Tongkou components, only the dual electrode with a rated voltage of 40V is only indicated, and the type of 4 parts is applicable:

1N5825

MBR745 type

80 square meters 045

Type 6TQ045

Step 7: CBOOST will use 0.01 μF capacitors. In this example, the adjustable output design examples need to from the battery vehicle power supply (voltage range 20V to 28V, typical large truck applications) to 14.8V DC transform power supply, which is usually used for electric electronic equipment from single battery 12V vehicle system Essence Load current requiresSeek the maximum 3.5A. It also hopes to implement the power supply of all surface installation components.

Step 1: The operating conditions are:

vout 14.8 volts

Maximum vehicle recognition number 28V

ILOAD maximum value 3.5a

Step 2: Select LM2678S-ADJ. To set the output voltage to 14.9V, you need to select two resistors (R1 and R2 IN Figure 2). For adjustable devices, the output voltage is set through the following relationship:

Among them, VFB is usually a feedback voltage of 1.21V. The recommendation value of R1 is 1K, so R2 is determined as:

R2 11.23 thousand euros

The closest standard 1%tolerance value is 11.3kΩ. Set to 14.88V, that is, within 0.5%of the target value.

Step 3: Use a line diagram for adjustable devices, Figure 6 Requires the calculation of the inductance volt microsecond constant (e T as V s) below) Formula:

Among them, VSAT is the voltage of the internal power supply. In this example, this will usually be 0.12ΩX 3.5A or 0.42V. VD is the voltage drop through the forward dual -Kisheryt diode, usually 0.5V.

Application prompt (continued)

The switch frequency of 260kHz is used to estimate the opening time of the switch, and the energy is stored in the sensor during this period. For this example, E T is:

The horizontal intersection of Figure 6,27V μs and 3.5A vertical line (ILOAD MAX) indicate L48 , 47 μH sensor, or L49, can use 33 μH sensors. Or the sensor is suitable, but the greater the inductance in this example, the smaller the ripple current. From Table 1, you can find the L48 in the surface installation component from the pulse engineering with the part number P0848.

Step 4: Use Table 6 to determine the output capacitor. With a 14.8V output-using 12.5 to 15V voltage, 47 μH inductance has three surface stickers output capacitors. Table 2 provides the actual capacitor characteristics based on the C code. The following options

can be used:

1 x 33 μF/20V AVX TPS (code C6)

1 x 47μF/20V sprague 594 (code C8)

1 x 47 μF/20V Camit T495 (Code C8)

Important precautions: The voltage application (less than 3V output) when the adjustable device is used at a low level, if the line diagram, Figure 6, select 22 μH or smaller inductance, Table 6 does not provide output capacitors solutions. Under these conditions, the number of output capacitors required for stability becomes unrealistic. It is recommended to use 33 μH or 47 μH sensors and output capacitors from Table 6.

Application prompt (continued)

Step 5: The input capacitor in this example requires a minimum 35V WV rated value, and the RMS rated current is 1.75A (maximum 1/2 IOUT). As can be seen from Table 2, C12, a 33μF/35V capacitor from SPRAGUE, the parallel of these capacitors of the rated current of the highest voltage/surface installation component will be appropriate.

Step 6: From Table 5, 5A or more Schottky diode must be selected. The surface installation of the diode with the surface of the safety and halo can be used under the rated voltage. One of the two diode can be used: MBRD1545CT 6TQ045S type

Step 7: CBOOST will use 0.01 μF capacitors. The LLP packaging device LM2678 uses the 14-draw LLP surface installation to allow a significant reduction in the equivalent power consumption compared with the TO-263. For detailed information on the standards of installation and welding, see the application description AN-1187.

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