General description

LM2578A is a switch adjustor that can easily set the DC-DC voltage conversion circuit, such as lowering voltage, boosting and reversing configuration. LM2578A is a unique comparator input level. It not only has an independent pin with reverse and non -reverse input, but also provides an internal 1.0V reference for each input to simplify the circuit design and P.C. board layout. This output can be switched to 750 mAh, and the output tube foot set electrode and transmitter can be used to improve design flexibility. The external current limit terminal can refer to the ground or vehicle identification number terminal, depending on the application. In addition, LM2578A also has a board oscillator that is used to set the switch frequency of a single external capacitor than 1hez to 100 kg (typical). LM2578A is an improved version of LM2578, providing a higher rated value for the total power supply voltage, and the output transistor transmission pole and the collector voltage.

Features

Input terminal reverse and non -reverse feedback inputs

1.0V reference voltage

Power voltage from 2V to 40V operation

The output current is as high as 750 mAh, the saturation is less than 0.9 volts

current limit and heat shutdown

The duty ratio is as high as 90%

Application

Anti -voltage, voltage, inverter, and single -end transformer configuration

motor speed control

flash

Absolute maximum rated value (Note 1)

Total power supply voltage 50V

The output of the set output-0.3V to+50V

The transmitter output of the transmitter (Note 2) –1v to+50V [ 123]

Power Consumption (Note 3) Internal limit

output current 750 mAh

Storage temperature 65 ° C to+150 ° C

Lead temperature (welding, 10 seconds) 260 degrees Celsius

The highest knot temperature 150 303C

ESD tolerance (Note 4) 2KV

Operating rated value

The environment Temperature range

LM2578A 40 ° C ≤ TA ≤+85 ° C

lm3578a 0 degrees Celsius ≤TA ≤+70 degrees Celsius

123] LM2578A 40 ° C ≤TJ ≤+125 ° C

lm3578a 0 degrees Celsius ≤TJ ≤+125 degrees Celsius

Electric characteristics

These rulesFan is suitable for 2V ≤Vin ≤ 40V (TJ ≤ —— 25 — C, 2.2V ≤Vin ≤ 40V), timing capacitor CT 3900 PF, and 25%≤ occupy a duty kitchen ratio ≤ 75%, unless otherwise regulations. The value in the standard font is suitable for TJ 25 ° C; the value in the black font is suitable for running within the specified working knot temperature range.

Electric characteristics (continued)

These specifications are suitable for 2V ≤Vin ≤ 40V (TJ ≤ — 25 — C, 2.2V ≤Vin ≤ 40V), timing capacitors CT 3900 PF and 25%≤ occupy a duty cycle ≤75%, unless there are other regulations. The value in the standard font is suitable for TJ 25 ° C; the value in the black font is suitable for running within the specified working knot temperature range.

Note 1: Absolute maximum rated value indicates the limit that the device may be damaged. During operation, DC and AC electrical specifications that exceed the rated working conditions.

Note 2: For TJ≥100 ° C, the emission pole pins voltage must not be lower than the ground 0.6V (see application information).

Note 3: At high temperature, the device must be reduced according to the heat resistance of the packaging. The 8 -pin immersion device must be at 95 ° C/W, and the ambient temperature is reduced at the connection. The equipment in the surface -installed component must be reduced at 150 ° C/W. At the junction of the environment.

Note 4: Human model, 1.5 kΩ with 100 PF series.

Note 5: Typical value is suitable for TJ 25 ° C, which represents the most likely parameter model.

Note 6: All limits guaranteed under room temperature (standard surface) and extreme temperature (thick body surface). The room temperature is limited to 100%production. By using the correlation of standard statistical quality control (SQC) method, the temperature limit is guaranteed. All limits are used to calculate AOQL.

Note 7: The input terminal can prevent accidental short circuits on the ground, but if the external voltage is higher than the reference voltage, the current should be limited to less than 5 mA.

Note 8: I1 and I2 are the external receiver current (reference test circuit) of the input terminal.

Note 9: Connect 10 kΩ resistors from pins 1 to pin 4 to maximize the driving duty duty, usually 90%. Applying the minimum current limit sensing voltage to sales 7 will not reduce the duty ratio to less than 50%. Applying the maximum current limit sensing voltage on the pin 7 will reduce the duty cycle to less than 50%. When the output amplitude of the collector is 40V or larger, the voltage may be increased by 15 MV to reduce the duty ratio to 0%(see the ground -reference current limit sensing voltage typical curve).

Test circuit*The test circuit shown in the parameter test. Use the required vehicle recognition number, collector voltage and duty -to -occupying ratio. The input digital voltage meter should use a resistor greater than 100 mΩ to measure the following content: input reference voltage to the ground; S1 is at any position. Horizontal displacement precision (%) (TP3 (V)/1V) x 100%; I1 i2 is S1 1 mia input current (mia) (1V tp3 (v))/1 mΩ: I1 i2 is s1 0 mAh. The oscillator parameters can be measured by frequency counter or oscilloscope at TP4. The current limit detection voltage can be adjusted by 0 to 1V to float the power supply, and the current limit terminal is connected to the current or vehicle recognition code terminal. Set the duty cycle to 90%, monitor the test point TP5, and adjust the floating power supply voltage until the LM2578A duty cycle has just reached 0%. This voltage is the current limit sensing voltage. When the power current should be measured at 0%with the duty cycle, it is S1 at the position of i1 i2 0 mAh. The LM2578A specifications adopt an automatic measurement test equipment. This circuit provides customers with convenient check parameters. Due to the changes in the test conditions, the test values may not match the test program of the factory.

The term definition

Input reference voltage: voltage (referring to ground) must be applied to the input of reversing or non -reversing the regulator switch ( Open or close). Entering reference current: The current that must be drawn from reversing or non -reversing inputs causes the regulator switch to change the state (open or off). Input level offset accuracy: This specification determines the output voltage control of the regulator output voltage control depends on the equal current and non-inverse input from the reverse (see the inverter of the inverter in Figure 21 and the RS-232 line drive power supply of FIG. 21 P. 23). Use two equal value test horizontal displacement precision to input the current from the inverter and non -inverter, and then measure the duty cycle output from the voltage switch generated by the resistor. Jet saturation voltage: When the reverse input terminal is connected to the ground with a 10 kΩ resistor and the transistor of the output end is transmitted, the setting electrode saturation voltage is the transmitting polar voltage set current under the given condition.

Transmitting polar saturation voltage: Connected to the vehicle identification number through the reverse input terminal grounding set of the 10 kΩ resistor and the output transistor, the transmitter saturated voltage is the setting electrode of the transmitted electrode to the transmitted polar voltage to the transmitted polar current Essence Collection electrode-transmitting pole maintenance voltage: The collector of the output transistor-transmitting polar breakdown voltage, measurement at the specified current. The current limit detection voltage: The voltage limit under current refers to the power supply or ground terminal, which will cause the output transistor to turn off and reset the cycle at the frequency of the oscillator. The current limit sensing current applies voltage is equal to the current limit sensing voltage. Power current: IC power current, excluding the current of the transistor when the oscillator works.

Function description

lThe M2578A is a pulse width modulator designed for use as the switch regulator controller. It can also be used for applications that need to control the pulse width voltage. A control signal usually means that the output voltage of the input compares the comparator of LM2578A with the reference of internal generation. The output of the error signal and the OS Cillator was sent to the logical network, and the logic network determined that when the output transistor was opened or turned off. The following is LM2578A. The comparator input level of the comparator input level LM2578A is the only reversal and non -reversing input that can be used to contain 1.0V references. As shown below: The 1.0V reference voltage is input to the modified voltage and follow the device circuit (see the function map). When both input pins are opened, no current flows through R1

Functional description (continued)

and R2. Therefore, the two inputs of the comparator will have a 1.0V reference voltage potential when input. For example, VA, for example, non -inverse input is pulled away from VA∏V, and the current of R1 is ∏V/R1. The same current flows through R2, and the comparator sees that the total voltage is 2∏V between it. The high gain of the system will correct this imbalance and return to the 1.0V level by feedback. This unusual comparator input level increases the flexibility of the circuit, while minimizing the total number of external components required by the voltage regulator system. For example, for example, you can set the switch to the configuration without using an external computing amplifier for feedback polar reversal (see typical applications). The oscillator LM2578A provides a vehicle oscillator that can be adjusted to 100 kilo. Its frequency is shown in a external capacitor C1, as shown in Figure 1, and follows the equation FOSC 8x10-5/C1 oscillator to provide a removal pulse to limit the maximum value to the duty cycle, and the internal circuit has a reset pulse [ 123]

Output transistor

The output transistor can output up to 750 mAh current saturation voltage less than 0.9V (see the saturated voltage and transmitting polar saturation voltage curve of the collector) Essence The voltage that pulls the transmitter below the ground must not exceed 1V (when TJ≥100 degrees Celsius, this limit is 0.6V). Because of this limit, one must use an external transistor to generate a negative output voltage (see the typical application of the reverse regulator). Other configurations may need to prevent violations of this limit (see the output part of the application information). The current limitation of the current limitation of LM2578A can refer to ground or vehicle recognition code pins, and run the basis according to the cycle. The current limitation part consists of two comparators: one non -inverter input voltage 110 MV is below the vehicle recognition number, and the other refers to its reverse input 110mv (see function chart). This current limitation terminal is pulled away from the vehicle identification number or grounded 110 millivolves.

Application information

current limitation

If function descriptionIn this, the current restriction terminal can refer to the vehicle identification number or ground terminal. The resistor R3 converts the current to the current limit detection voltage.

Temporary restrictions

When the peak of noise and switching transient interference correct current restriction operation, R1 and C1 are used as a control flow limit circuit response Low -pass filter time. Because the changing current of the current limit terminal is based on the reference position, the R1 should be less than 2 kΩ when the ground is less than the ground, and less than 100Ω when the vehicle recognition number is mentioned.

C, L. When the inductive voltage multiplies requires a larger sensor resistance value, the voltage can use a segmentation network composed of R1 and R2. This effectively multiplies the induction voltage (1+R1/R2). Also, the diode can be used instead of R1 to increase the current limiting sensing voltage of about 800 millivoltors (diode VF+110 millivolt).

Impurd pressure atresia

IOU was a component that was completed under few external conditions. When the vehicle identification number is lower than Qina, the output transistor is closed. This occurs, because the diode D1 will then become positive bias, allowing the resistor R3 to absorb the parallel combination of the parallel combination of R1 from the non -inverter input to absorb larger currents and R2 of the reverse terminal. R3 should be parallel of R1 and R2.

The maximum duty cycle limit

By adjusting the charging and discharge ratio of the oscillator capacitor, the maximum duty cycle can be limited only one external resistance. The typical value is 50 micro -safety charging currents, the discharge current is 450 micro -safety, and the voltage fluctuates from 200 millivolttur to 750 millivolves. Therefore, R1 is the required charge slope to select the C1 being re -adjusted to set the oscillator frequency

The duty cycle adjustment

When you need to manually or need to be manual or need to be manual or need to be manual or required When the mechanical selection of the output transformer's duty ratio, the circuit shown below may be used. The output will drop at each current to R2 and the R3 from non -reversing terminals becomes greater than the current sinking from the inverter terminal. As shown in the figure, the R3 can be used to adjust the duty cycle from 0%to 90%. When the sum of R2 and R3 is twice the R1 value, the duty ratio is about 50%. C1 may be a large electrolytic groove to reduce the frequency of the oscillator to a capacitor below 1hez.

Remote shutdown

LM2578A can be remotely shut down from the non -inverted input current than from the reverse input. This can achieve R2 parallel by selecting the resistance R3 about half of the R1 value.

The output of the transmitter

When LM257When the 8A output transistor is disconnected, if the transmitting pole output voltage is lower than the ground pins voltage output transistor, it will be opened because its base is clipped to the ground. The transmitting polar output is a low -connected curve, the electric current current indicates the relationship between the collector current in this mode and has the relationship with the temperature and the transmitting polar voltage. When the e-electrode-transmitting pole voltage is high, the current will be avoided in the output transistor and should be avoided. This situation may occur at the BUCK application under large current high voltage. If the forward voltage drop of the posterior tube with a transmitter output and the CATCH diode is greater than 0.6V, it can be connected to the emission polar tandem to add the diode output to offset the positive voltage drop of the capture of the diodes ( See Figure 2). In order to improve the efficiency antihypertensive regulator of high output current, the external PNP transistor is applied to as shown in Figure 16.

Synchronous device

When operating multiple devices at the same time, the oscillator can be applied through an external signal. The driving signal should be the maximum pulse width of the pulse waveform is 2 microseconds, and the amplitude is

Application information (continued)

1.5V to 2.0V. The signal source must be 1. ) Drive capacitance load and 2.) provide each LM2578A with up to 500 Weian. The choice of capacitor C1 to CN is slower than the synchronous frequency

Typical application

LM2578A can be conducted in a continuous or discontinuous conduction mode. The following applications (except for the booster booster regulator) are designed for continuous conduction operations. In other words, sensor currents are not allowed to fall to zero. Compared with the DIS continuous mode, this operation mode is higher and EMI has lower characteristics. The boost regulator buck configuration is used to reduce the input voltage to a lower level. The transistor Q1 in FIG. 14 cuts the input DC voltage into a square wave. This square wave is a low -pass filter consisting of L1 and C1. The duty cycle D waves use the following equation to the output voltage and input voltage:

Figure 15 is a 15V to 5V antihypertensive regulator with output current, IO, 350 mAh. The circuit is 20%IO (maximum), the output voltage ripples are 10 millivolves, the efficiency is 75%. Route adjustment. The choice of component values is as follows: R1 (VO 1) X R2, where R2 10 kΩr3 v/isw (maximum value) R3 0.15 Euro

V is the current limit sensing voltage, 0.11visw (MAX) is a maximum allowable current transistor by output. L1 is an inductance, you can find the calculation diagram from the inductance (Figure 16) as follows: Given vehicle identification number 15V

vo 5 volts

IO (maximum value) 350 mAh [ 123]

FOSC 50 kgen

Different from 20%at IO (maximum value).Note that because the circuit will be discontinued in IO (maximum value) at 20%, the load current shall not be less than 70 mAh.