The current mode control PWM

The switching frequency is as high as 1MHz

The start current low ( lt; 120μA)

The constant output power and switch frequency

Suitable for suitable Large current output drive

Power MOSFET (1A)

full lock PWM logic with dual pulse inhibitory

A programmable duty duty

100% And 50%maximum duty cycle limit

programming soft start

Over -current fault detection and re -launch delay

Pwm UVLO

] Input/output synchronization

Lock disabled

current response internal 100ns cutting edge blank blank

Packaging: DIP16 and SO16N

Instructions

This is this The main controller is a technology developed in BCD60II and has been designed to control the use of fixed frequency current mode. Based on the standard current mode PWM control device, this device has the following characteristics that can be programmed and soft startup, input/output synchronization, disabled (for overvoltage protection and power management), accurate maximum load cycle control, 100NS frontier discharge hidden turnover current detection The ""constant power"" function of the pulse current limitation, over -current protection, soft start intervention, and control of output multi -simultaneous monitor switching power supply.

Electrical features (VCC u003d 15V; TJ u003d 0 to 105 ° C; RT u003d 13.3K ; ct u003d 1NF unless there are other regulations.)

Electrical characteristics (continued)

The constant power function

The pulse voltage restrictions prevent peak values u200bu200b

The current current exceeds the given level. This in turn limits the maximum power of the output. In other words, the performance of the power converter. But the ability depends on the switch frequency: for example, a discontinuous current mode is exciting. They are only proportions. Display switch frequencies in the SMPS of the grating CRT scanning signal with the grating line of the display to increase the antidity. When more and more, the CRT display needs to be in the range of different video frequency (e.g. from 31kHz to 64 kHz), so the number of switching frequency will also change in this range. In some faults, the power throughput may be excessively excessive without having to trip up the pulse current limited circuit high operating frequency. For safety reasons, doing so is the power of the design converterGrade (power MOSFET, transformer, capture diode), so as to withstand maximum power throughput under the fault conditions. However, this is an unsustainable growth of scale and cost. Overcoming this ""constant"" function. The device changes its pulse threshold through the pulse current to maintain its pulse threshold to maintain the power capacity of the reverse transformer although the switching frequency has changed. This is a value of 1 (synchronous) with the value of the error amplifier (VCOMP), which is reduced by the signal frequency of the input pin. The required frequency voltage conversion can achieve this function by maintaining the peak voltage of the circuit detection (synchronous) oscillator with a peak value. Only an external capacitor. It is important to point out the shape of the shape. The duration of the amplitude synchronization pulse is nothing to do with this technique.

Application information

Detailed pin function description

Pin pin 1. Synchronous (input/output synchronization). This function allows IC oscillator to synchronize (or other controllers) external frequency (from). As the main pulse, the pin is passed on the positive pulse of the oscillator (see pin 2). Triggered at the edge of the subordinate operation circuit. Reference is shown in Figure 21. When several IC parallel work does not have the designated needs, because the fastest one automatically becomes the main control. During the rise of the oscillator's slope, the pins were pulled down by the leakage current of the 600 μA. At the edge of the decrease, the pulse is released, and the 600μA is turned off and cut off. The power of a generator is usually 7 mAh (the voltage is still higher than 3.5V). In Figure 20, some practical examples of synchronous L5993 are given. Needle 2. RCT (oscillator). Resistance (RT) and capacitors (CT), as shown in Figure 21, set the operating frequency FOSC of the oscillator. CT is charged through RT until its voltage reaches 3V, and then quickly discharge. As a voltage drop to 1V, start charging again. The frequency can be used in Figure 13 or considering the approximity value relationship:

It and: td #8773; 30 #8901; 10-9+kt #8901; CT (3) TD is also the duration of synchronous pulses

At 1st pin, define the duty duty range DX (DX definition see shiny 15 and pins 15 and and calculate). However, if V15 is connected to VREF, the system's switch frequency is half FOSC. If IC is synchronized with the external oscillator, the FOSC should select RT and CT to be lower than the main frequency (usually 10-20%), depending on the tolerance RT and CT.

Pink pin 3. DC (duty duty control). Performing this needle -pin voltage between 1 and 3 V is possible to set the maximum duty ratio at 0 and upper limit DX (see pin 15). If DMAX is the maximum duty ratio required, the voltage V3 applied on the pin 3 is: V3 u003d 5-2 (2-DMAX) (4) The internal comparative comparative comparison between the DMAX through the V3 and the oscillator slope (see Figure 22). Therefore, if the device is synchronized with the external frequency FEXT (therefore the oscillator is reduced), (4) becomes:

Voltage below 1V will inhibit the drive output stage. This can be used for non -locking devices, such as under overvoltage protection (see application concepts). If there is no need to limit the maximum duty ratio (ie dmax u003d dx), the sales must keep floating. Internal pull (see Figure 22) can keep the voltage above 3V. If you insert the noise (for example, during the ESD test), it can be connected to VREF through 4.7k resistors. Needle 4. VREF (reference voltage). The device is to provide accurate voltage benchmark (5V ± 1.5%) that can transmit some milliam circuits to the outside. Small film capacitors (a typical value of 0.1 μF), connected between the pin and SGND, it is recommended to ensure the stability of the generator and prevent the noise that affects the reference. Before the device is turned on, this pins have a leakage current of 0.5mA.

needle feet 5. VFB (error amplifier reverse input). This feedback signal is applied to this pin and compared with E/A internal reference (2.5V). This E/A output generates a control voltage

Correcting the duty cycle. E/A uses high -gain bandwidth products, which can broaden the overall control loop, high conversion rate and current capability, and improve its signal characteristics. Generally, the compensation network that stabilizes the entire control loop is connected between the pin and COMP (pin 6).

Pin pin 6. Comp (error amplifier output). Generally, this pin is used for frequency compensation and related network connections between the two

pin and VFB (pin 5). Since L5993, the compensation network cannot ground E/A is a voltage mode amplifier (low output impedance). For some tests for compensation technology, see the application ideas.

Pinper 7. SS (soft start). When the device starts, connect to this pin and SGND (pin 12) During this period, about 7 volts of slope, E/A output by the voltage of the E/A output is css itself , Until the stable state value given by the control loop. The maximum interval time during the E/A clamping period, the reference soft startup time is about:

in the formula, RSENSE is a current fluid resistor (see needle pin 13). IQPK is the peak current of the switch (flow pass through the flow pass (flow passes through the pass passing. RSense), depending on the output loading. Usually, for TSS, the choice of CSS is usually milliseconds.

As mentioned earlier, the soft start -up intervention can also be used for severe overload or short -circuit output. Refer to Figure 23. The pulse current is limited to a certain extent. It is effective to reduce the connection time of the power switch (from A to B). After the shortest connection time is reached (starting from B), the current is controlled. To prevent this risk, the comparator triggered the current processing program, called the ""HICCUP"" mode when the voltage was higher than 1.2V (point C) (Isen, pin 13). Basically, the IC is closed, and then the soft start is just detected. As a result, the operating point suddenly moved to D, and the folding effect was created. Figure 24 shows the operation. The oscillating frequency appeared on the software

Start the capacitor when permanent fault. Reference to the ""snoring"" period, which is similar to the following formulas:

Since the system will try to restart each fault cycle, there is no risk of locking. The ""snoring"" causes the system to be controlled to prevent short circuits, but it cannot eliminate the stress of the power element during the period of pulse limit (from A to C). If you can better control overloads, other external protection circuits are required.

Pink pin 8. VCC (controller power supply). This needle provides a signal part of an integrated circuit. The device can be enabled as the VCC voltage exceeding the starting threshold and as long as the voltage is higher than the UVLO, it can work threshold. Otherwise, the device will be closed and the current consumption will be extremely low ( lt; 150 μA). This is the most important contribution to reducing the consumption of the starting circuit (only one resistor), which is the most important contribution to power loss. When the converter is light load. The internal Ziner limits the voltage on the VCC to 25V. If this limit is exceeded, the IC current consumption will increase significantly. A small film capacitor (needle feet 12) between this pin and SGND is as close to the IC as much as possible to filter high -frequency noise.

Pink pin 9. VC (power -level power supply). IT supply the drive of the external switch, so AB absorbs pulse current. Therefore, it is recommended to place a buffer capacitor (toward PGND, needle foot 11, as close as IC as much as possible) to maintain commotion in order to avoid these current pulses. This pin can be connected to the buffer container directly or through the resistor, as shown in Figure 25, control the external speed of the switch MOS switch respectively. During the drive, the gate resistance is RG+RG ', and the AT shutdown is limited to RG.

Pin pin 10. Output (drive output). This pins are the output switch of the external power drive level. Generally, this will be a power MOS, Al, although the power of the driver is enough to drive BJT (1.6A source, 2A exchange, peak). The driver consists of a totem rod and a high -side NPN Dallingon and a low -side VDMOS, so there is no need to clamp the external diode to prevent the voltage from being lower than the ground. The internal clamping is limited to 13V transmission to the gate voltage. Therefore, it can be provided with a higher -voltage drive (pin 9), without any damage to the oxidation layer of an external MOS grid oxide. Piece will not cause the power consumption inside the chip, because door chargeThe peak of the current appears in the gate voltage, and clamping is not positive. Moreover, when the gate voltage is 13V, it is steady.

In FIG. 26), in order to ensure that the external MOS cannot open the account tally. This circuit is characterized by the same receiver capacity (usually 20mA@1V) from VCC u003d 0V to the startup threshold. When the threshold is exceeded, L5993 starts to work, and VREFOK is pulled up (reference picture. 26) circuit fails. Then you can omit the ""deflection"" resistor (connected between the door and the source (MOS) is usually used to prevent the connection of an unpopular external MOS due to some leakage currents.

Pink Power supply). The current circuit is closed through this pin during the discharge of the external gate. This cycle should be as short as possible to reduce electromagnetic interference and operation from the signal current loop.

]

Pink 12.SGND (Signal grounding). This grounding refers to the control circuit of an integrated circuit. Therefore From flowing through the SGND path.

needle pin 13.isen (current feeling). This needle connect to the current ""heat"" influenza -influenza resistor RSENSE (another ground) to get a voltage slope. It is a switch The image of the current (IQ). When the voltage is equal:

The conductivity of the switch is terminated.

In order The ""consumption"" of about 100NS is realized internally as shown in Figure 27. Therefore, the RC filter between the smooth pin and RSENSE can be moved again, or at least it can be greatly reduced. . When the voltage rises to 2.5V above 2.5V, the IC shutdown needs to pull VCC (IC power supply voltage, pin 8) lower than the UVLO threshold to allow the device to restart. Below, as shown in the figure. 28 can also achieve overvoltage protection. If the ""Application"" section shows it, use a filter capacitor to pins this pin to avoid the peak of noise. If not, it must be connected to the middle to the middle Scholar. Pink 15. DC-LIM (maximum duty cycle limit). The upper limit DX of this duty cycle is depending on the voltage applied to the pin. 123] If DC-LIM is grounded or keeps floating. On the contrary, connect DC-LIM to VREF (semi-occupied ratio operation), DX will be set to:

The switching frequency Half of them

For an oscillator, internal T triggers (see square diagrams, Figure 1) are activated. Figure 29 shows the operation. The semi-occupation ratio option accelerates the discharge of the timer capacitor CT (for the duty cycle to be as close to 50%as much as possible), so the frequency of the oscillator-the same RT and CT-will be slightly higher. The reduction of frequency can be used to reduce the requirements that must meet the requirements of energy consumption (such as the display, see ""application ideas"").

needle 16. C-power (constant power function). The external capacitor SGND connected between this pins completes the peak of the peak of the circuit detection. The circuit obtains a DC voltage (with the increase of the synchronous frequency pins 1 (synchronous) ascending) to restrain error amplifiers output (VComp), as shown in the detailed internal schematic diagram of Figure 30. In this way, the frequency of 47K discharge resistance is reduced when the pulse setting point is rising by the movement frequency. External capacitors must be enough to get a real DC voltage on the pin. Considering that the minimum extension capacitance value (CCP) of the resistor internal 47K the 1%ripple of the 1%ripple that is smaller than overlapping on the DC voltage is:

, the #402; min (Hz) is the minimum synchronization frequency.

When this function is not used, the pin 16 must be connected directly to the pin 4. Considering the transformer, the circuit is usually not adjusted. No matter how to change the maximum power limit of the switching frequency and/or the power supply voltage, minimize the following or more to minimize the following or more

-Litor inductance;

-D number ratio of transformer turning;

-Strequent running frequency;

-The induction resistor.

Requires a test process, including the easier to modify parameters. In fact, the combination of specific parameters and DE depends on the range of power voltage and synchronization frequency range.

The additional ""fine -tuning"" can be achieved in the current (13, Isen). For a wide range of power applications, this is the propagation path of the compensation current detection path no matter how to compensate the current detection path (PWM comparator+闩 lock+drive), the circuit is shown in the ""application concept"" part.

Layout Tips

Generally speaking, the correct circuit board layout is critical to the correct operation, but it is not easy. Be careful to place components, correct wiring, and appropriate trace width. If high voltage, it meets the main problems of the isolation distance. L5993 is complicated by using the two pins for separate current bias (SGND) and switch drive current. It will only remind several important issues here.

(1) Return all power signals

(grounding, shielding, etc.) should be wiring separately, and only a single location.

(2) The noise coupling can be limited by the minimized current ring.This is particularly suitable for high pulse circuit water flow.

(3) For the high current path, it should be on the other side of the PCB: this will reduce the two resistance and the induction of the line.

(4) Magnetic field radiation (and mixed inductance) can reduce the switching current as short as possible by retaining all traces.

(5) Generally speaking, the trajectory of carrying signal current should be far away from the traces of the pulse current or the voltage of the voltage.From this view, you should be particularly careful of high impedance points (current influenza input, feedback input, etc.).It may be a good idea on the PCB side and the other with power sources.

(6) Points of some important circuits, such as reference voltage, IC power pins, etc.